17 ms·

Teardown of a PC Power Supply

407 points by parsecs 5y ago

walrus01 5y ago
If anyone wants to see a really top quality PC power supply, for comparison to a cheap one, take a look at the board and layout on a $100 seasonic power supply. Well known Taiwanese power supply company that doesn't try to compete on cheap prices and has been around for 20+ years.
- ta988 5y ago
  http://www.kitguru.net/wp-content/uploads/2014/08/DSCF2160.jpg http://www.kitguru.net/wp-content/uploads/2014/08/DSCF2160.j...
  - judge2020 5y ago
    They use hotlink protection to prevent other sites from embedding their images - you'll have to view that image from https://www.kitguru.net/components/power-supplies/zardon/seasonic-x-series-1050w-power-supply-ss-1050xm2/5/ https://www.kitguru.net/components/power-supplies/zardon/sea... or open it in a new tab.
    - ta988 5y ago
      Oh sorry, I didn't realize that.
amelius 5y ago
It would be nice if the article showed some voltage or current plots for various places in the circuit.
robbmorganf 5y ago
I never realized the main transformer element worked on rectified AC. Could someone explain why we rectify the AC power before the transformer? I always thought transformers worked on AC power anyways.
- cristoperb 5y ago
  In switching mode power supplies like this, the mains AC is rectified and then chopped up into higher frequency pulses and fed to the transformer. The higher frequency allows for smaller transformer. It also allows for voltage regulation because the input pulse width (in this case via the UC3842B controller IC) can be altered based on the sensed output voltage.
- RL_Quine 5y ago
  50/60hz requires a large transformer core. Switching power supplies rectify to DC, then drive the transformer at potentially megahertz which increases efficiency and substantially reduces the size and weight of the core. For similar reasons aircraft use 400hz 115v supply as it makes all of the power conversion electronics dramatically smaller.
  - londons_explore 5y ago
    To add to this... A transformer converts electrical energy into a magnetic field and back into electrical energy. All the energy from a single 'sine wave' must be stored in the magnetic field inside the transformer briefly before coming out of the output. The transformer core is made of steel usually. For a given weight of steel, there is a maximum amount of magnetic energy it can store. That means that at low frequencies like 50/60Hz, transformers end up very bulky.
    - whoisburbansky 5y ago
      Wasn’t immediately clear from GPs comment and my admittedly limited physics instruction, but the way you explained it made it seem incredibly obvious in retrospect, which is a rare skill, thanks!
  - jeffbee 5y ago
    The standing field in a massive 60Hz transformer also necessitates robust inrush protection. With a transformer across the mains, losing the input power momentarily can cause a huge surge current when the input is reapplied. With the bridge and filter first, the inrush from being momentarily switched off won't be severe.
marcodiego 5y ago
I generally think of a switching power supply as a PWM damped by a capacitor. Never knew exactly how oversimplified my thinking is.
- amelius 5y ago
  The problem with this view is that a capacitor at a low impedance output will do nothing.
  - marcodiego 5y ago
    Hmmm... makes sense. Is it possible to ELI5 what should be put after the PWM so it can handle low impedancies? From https://www.electronics-tutorials.ws/power/switch-mode-power-supply.html https://www.electronics-tutorials.ws/power/switch-mode-power... "The Buck Switching Regulator" looks like an arrangement with a diode, inductor and capacitor is enough. Interesting.
    - amelius 5y ago
      The link you found explains it well, but there is a different perspective if you want to focus on impedances. The idea is to drive the capacitor with a high impedance. This impedance should not be a resistor, because a resistor will limit current (more current means a higher voltage drop in the output), further it will consume power and become hot. Instead, you should look for something that works more like an ideal current source. An ideal current source has an infinite output impedance (because loosely speaking the impedance R=dv/di and di=0 for an ideal current source). A constant current source is a good fit for charging a capacitor since a constant current means a constant dv/dt slope. Now, as your link shows, a switching power supply does not have a constant current source in its main circuit, but it does use an inductor which has similar characteristics since inductors resist changes in current. The governing equation of an inductor is v=L*di/dt, and for the output impedance of the inductor you get loosely speaking R=dv/di =L/dt, which is large for large L and short timescales (dt close to 0), hence the similarity to an ideal current source. Now the driving part of the circuit at the left of the schematics in your link is a voltage source. So to drive an inductor, you use a voltage source. And to drive a capacitor, you use a current source. Inductors can be seen as current sources, and capacitors can be seen as voltage sources. I hope this explains it.
Scene_Cast2 5y ago
I wonder where the losses are, and if GaN power transistors for switching would help with efficiency here. I like Seasonic's fanless series, but wouldn't mind getting a bit more power out of the same size PSU.
- londons_explore 5y ago
  There are losses in every step, and power supply design is basically a big optimization problem to choose all the design parameters to minimize losses. The main components with losses: * The input capacitors are non-ideal and have some resistance. That resistance causes heat every time current flows in or out of them. * The MOSFET switch has an 'on resistance' which means it wastes energy when current flows through it. * The MOSFET takes a certain time to turn on or off. During that time it is partially on, which wastes a bunch of energy each switch. * The transformer has resistance in the coils. * The transformer has iron core hysteresis, which makes the steel of the transformer get warm as magnetic fields change in it. * The diode on the output side has voltage drop across it. * The capacitor on the output side has resistance.
  - quercusa 5y ago
    It was a real learning experience moving from ideal transistors to real MOSFETs in an H-bridge driving a motor. Gate capacitance led to lots of expensive smokefests.
- R0b0t1 5y ago
  They do help. Since HN finds it interesting I can write some on the most modern designs. I am currently designing a FOSS power supply. One of the goals is to go for high efficiency. The end product will use GaN and SiC elements. The different chemistries give different switching characteristics. (Interesting aside is that some topologies can run forward as line conditioning AND backwards as a motor inverter.) There are also supply chain and security considerations, though. You can buy magic PSU chips but what if you can't?
  - Scene_Cast2 5y ago
Gys 5y ago
I am pleasantly suprised this does not have its own internet connected microcontroller. So at least one element that is still not hackable.
- BenjiWiebe 5y ago
  Internet connected microcontrollers weren't very common in 2005.
  - Gys 5y ago
    Ai, missed that part! Thanks.
londons_explore 5y ago
Bear in mind this is a very old power supply. A modern supply would use the same principles, but would probably have mostly surface mount components, a single controller IC, and probably separate switching supplies for each different supplied voltage.
- kens 5y ago
  The power supply is from 2005. By my standards that's not very old, but maybe because I've also been looking at power supplies from the 1940s :-) Specifically a 100-pound Teletype power supply from the Navy that used mercury-vapor thyratron tubes. http://www.righto.com/2018/09/glowing-mercury-thyratrons-inside-1940s.html http://www.righto.com/2018/09/glowing-mercury-thyratrons-ins...
  - quercusa 5y ago
    Two great articles, Ken!
- dfox 5y ago
  Last time I looked at it it was not especially cost effective to build PC power supplies on multilayer boards. That leads to exactly the kind of construction as in this power supply: large almost completely through hole single-sided board with power components and one or more higher density perpendicular sub-boards with control logic.
  - londons_explore 5y ago
    2 layer boards with smd components are now cheaper than single layer and through hole - simply because through hole requires more labour to place components and has a substantially higher failure rate (bad joints). Obviously some components in a power supply still need to be through hole for mechanical reasons, but it isn't many.
    - dfox 5y ago
      It is not that clear-cut. Obviously the optimal case is SMD-only, but there is a threshold when THT-only becomes cheaper than SMD/THT mix. Another thing is that power supplies tend to use higher temperature board material (presumably to allow for thinner copper plating) which is somewhat rare and expensive in dual layer configurations.
janci 5y ago
Server power supplies are impressive. I pulled out some PSUs from old scrapped servers. In a smaller form factor than ATX they deliver more than 1kW power. You read that right. 100A at 12V actually.
- snypher 5y ago
  100A over how many 12V circuits? I doubt it is just a single circuit, or you would need a ~4AWG cable and rated connector?
  - ptomato 5y ago
    from the PSU typically one (on hotswap supplies); e.g. on https://cdn11.bigcommerce.com/s-qfzamxn9kz/images/stencil/original/products/130535/437709/570451-001-2__86092.1579103875.jpg?c=2 https://cdn11.bigcommerce.com/s-qfzamxn9kz/images/stencil/or... the connectors on the left are just control/sense pins and the big beefy ones are a single 12v & ground.
  - namibj 5y ago
    They plug in via an edge connector straight into the mother board, or sometimes into a separate board that connects to the mother board.
  - deleted 5y ago
    [deleted]
- LargoLasskhyfv 5y ago
  Only if you are deaf. Otherwise they are annoyingly loud. Whhhhsssssssss
flyinghamster 5y ago
The real treats were the bottom-of-the-barrel PSUs. I remember having to deal with a slew of these at work back in the early aughts. I remember turning on a machine one day... sssFWSSSSSSSHH and the magic smoke came pouring out. It would up taking out the the motherboard and hard drive with it. I autopsied the dead power supply, and it was chock full of capacitors (some blown-out) marked "Rulycon" (note, not Rubycon).
- LargoLasskhyfv 5y ago
  Name is program. Rulers of con ;->
nickpeterson 5y ago
Just an observation from years building computers. Never cheap out on power supplies. Always buy one (don't use one included in a case), and buy one rated 25-30% above what you think you'll need. Some of the most aggravating troubleshooting you'll ever endure can be avoided entirely.
- monocasa 5y ago
  Towards that end does anyone know if there any ATX power supplies that will stream out their sensor info over a serial port or something? It'd be nice to have power monitoring on that side of the mainboard's power regulators and caps, to pick up marginal issues before they get filtered out, and the power supplies these days will have a little ucontroller with all that information anyway without the mainboard having to duplicate that monitoring circuitry in the right place. For what's such an important piece of a computer there's so little introspection for data while in use that has to be being collected regardless. Yeah, you can always hook up a oscope or what have you, but catching it in the act of being marginal early on would have saved me more hours in my life than I'd like to admit.
  - daper 5y ago
    Server PSUs support such communication (looks like this is PMBus protocol, variation of SMBus, which is variation of I²C). In servers it's connected to the BCM and usually allows to read input and output power, FAN speed, temperatures and status (good/bad). The BCM often records historical data, including peak power (in last 1h, 24h), etc. After quick searching is looks there are people reading this info with a MCU [1]. But I think it would be hard to find such PSU in ATX form factor. [1] https://github.com/sxjack/dps750tb_psu_i2c https://github.com/sxjack/dps750tb_psu_i2c
  - dendriti 5y ago
    Whenever I experience issues which are likely related to a power supply, it is much easier to drop in a known-good replacement than to spend time diagnosing the specific issues. Also better to remove a potentially faulty PSU before it damages much more expensive hardware.
cesarb 5y ago
> The secondary circuitry produces the four output voltages: 5 volts, 12 volts, -12 volts, and 3.3 volts. [...] The power supply also provides a negative voltage output (-12 V). This voltage is mostly obsolete, but was used to power serial ports and PCI slots. And even older PC power supplies also provided a -5V voltage, the corresponding pin on the ATX connector is now (according to Wikipedia) a reserved pin. This progression also shows in the expansion slot standards: the ISA slot had pins for -5V and -12V; the PCI slot removed the -5V pin; and the PCIe slot finally removed the -12V pin. That is, a motherboard without any ISA or PCI slot, and without a RS232 socket or header, has no use for the -12V voltage. And there's already a newer power supply standard, called ATX12VO, which simplifies the power supply by providing only 12V (and a separate standby 12V). There's already at least one motherboard built for that standard: https://www.anandtech.com/show/15763/first-atx12vo-consumer-motherboard-the-asrock-z490-phantom-gaming-4sr https://www.anandtech.com/show/15763/first-atx12vo-consumer-...
- bruce343434 5y ago
  > -12v, -5v What prevents one from just wiring mobo.5v to port.gnd and mobo.gnd to port.-5v? That would effectively create a -5v potential between port.gnd and port.-5v
  - formerly_proven 5y ago
    -12 V was used for RS-232, which uses +12 V and -12 V levels (with a very wide tolerance band). Having a separate supply for this was a design decision which was pretty much instantly obsolete with integrated charge pumps: All RS-232 outputs are running off of charge pumps running at (-2) and (+2) ratios, so +-10 V levels with a 5 V supply. I don't know what -5 V was used for. Maybe some analog circuits somewhere, very early MOS logic also often had awkward supply voltages (charge-pumps made this obsolete too, just like high-voltage supplies for EEPROMs).
    - kens 5y ago
      Early DRAM chips like the MK4116 required -5 V, +5 V, and +12 V. (-5 was the substrate back bias for the chip.) So the ISA standard required -12 V, -5 V, +5 V, and +12 V.
Animats 5y ago
Some components, mostly capacitors, have the wrong hole spacing for their pins, and leads were bent to fit. That suggests part substitutions during assembly. Many of the through-hole components were not pushed all the way down into the board. That suggests overworked assemblers. This was obviously hand-assembled. The author makes a point that there's a clear division between the AC line side and the DC side. That's required for UL approval, but power supplies do show up without it. The power transformer that crosses the boundary should also have a split bobbin, so the AC line side coil and the output side coil are separated by a barrier, not wound on the same bobbin. There are worse power supplies.[1] [1] https://linustechtips.com/topic/515473-teardown-and-review-of-the-turbolink-atx-xg500w-crappy-psu/ https://linustechtips.com/topic/515473-teardown-and-review-o...
- lmilcin 5y ago
  > The power transformer that crosses the boundary should also have a split bobbin, so the AC line side coil and the output side coil are separated by a barrier, not wound on the same bobbin. Separate bobbin is not required for robust isolation. For example, just right now on my bench there is a medical separation transformer. No separate bobbin (hint: it is toroidal).
- formerly_proven 5y ago
  I have never seen a split bobbin in an ATX supply — they are bad for efficiency.
- GekkePrutser 5y ago
  There's worse power supplies sure but this one is still a mess. I don't see anything obviously dangerous but it's still a dirty ugly design and assembly. Other companies like Delta Electronics manage to cram lots of components in small spaces too but they actually do a good, clean job. Most PCBs with large, heavy through-hole components are still manufactured by hand, by the way.
  - deleted 5y ago
    [deleted]
  - 5y ago
bonoboTP 5y ago
Even if you're a "computer person" who is comfortable messing with the internals of a PC, be very careful with the power supply. Opening it up should really be left to professionals. Capacitors can remain charged for a long time after disconnecting the power cord. If despite all the warnings, you open it up to fiddle with internals because you think you understand the components and can pay attention not to touch things, at the very least, use only one hand at a time to avoid creating a circuit through your heart. In most other parts of the computer the worst that can happen in most cases is that you damage the computer, the power supply is different, there you also have a good chance of getting shocked.
- parsecs 5y ago
  Also a good tip to touch things with the back of your hand first, as the current can't force you to grip harder. This is more for line connected stuff though.
  - LambdaComplex 5y ago
    An even better tip would be to use an insulated screwdriver instead of your hand. Or even a capacitor discharge tool, since those apparently exist.
    - Scoundreller 5y ago
      When I had to do an air conditioning capacitor, I used a piece of wood with a nail. I couldn’t tell if adding steel wool to the mix would be a good idea or not.
      - baud147258 5y ago
        Wouldn't steel wool catch fire when exposed to an electric current? It might be useful to indicate there was still some charge in the capacitors, though
        Scoundreller 5y ago
lini 5y ago
ATX12VO[1] is a proposed major change to PSUs that hopefully will come in the near future. It will mean simpler (cheaper) designs and improved efficiency. I hope that the DIY market adopts ATX12VO before my next upgrade. Currently only OEMs have the ability build PCs with these kinds of PSUs. [1] https://www.intel.com/content/dam/www/public/us/en/documents/guides/single-rail-power-supply-platform-atx12vo-design-guide.pdf https://www.intel.com/content/dam/www/public/us/en/documents...
- dhdc 5y ago
  ...which puts all the DC conversion on the motherboard. Honestly, I can't tell if this is a good thing or a bad thing. On the plus side, power supplies will be much simpler to design and test, with potentially better efficiencies. On the other hand, all those additional DC-DC converters will take up quite a bit of space on the already crammed boards, and now you got more heat to manage.
  - agumonkey 5y ago
    fair point
  - formerly_proven 5y ago
    It recognizes how things are already. The 5 V and 3.3 V step-down converters in the PSU are pretty much only for Molex/SATA-connected peripherals, and those don't use 3.3 V anyway (99.5 % of them), since it's not guaranteed to be there. So the 3.3 V rail is pretty much pointless. 5 V not quite as much, but even in an enthusiast-level PC there will be probably just a handful of things actually connected to that - most likely SSD/HDD and maybe something like a fan controller. No heavy loads are connected to the 5 V / 3.3 V rails. Those are all supplied through the 12 V rail.
    - dhdc 5y ago
      I am pretty sure M.2 uses 3.3V exclusively, and depending on the implementation, RAM sometimes gets its power from down regulated 3.3V as well. Though you do have a good point, nobody misses -12V and -5V.
celim307 5y ago
On a somewhat related note, I just found out johnnyguru, a major contributor to consumer psu reviews and knowledge, has shut down his site and forums. His tear downs were always fascinating https://web.archive.org/web/20210126113732/http://www.jonnyguru.com/forums/archive/index.php/t-16610.html https://web.archive.org/web/20210126113732/http://www.jonnyg...
- 45ure 5y ago
  Some accrued knowledge still survives, within a community, which is trying to keep it alive. I wish them all the luck. http://www.johnnylucky.org/power-supplies/psu-recommendations.html http://www.johnnylucky.org/power-supplies/psu-recommendation... https://hardforum.com/forums/power-supplies.93/ https://hardforum.com/forums/power-supplies.93/
- PragmaticPulp 5y ago
  The computer enthusiast market is a difficult niche to cater to online. Most of the visitors will arrive with ad blockers enabled and they’re going to buy products from the cheapest retailer directly, not through affiliate links. Also, some of them will be brutally combative for no particular reason. The originator of that website landed a dream job doing R&D for Corsair. The owner of the domain (not Johnny, as far as I can tell) simply decided to let it expire.
- flyinghamster 5y ago
  I tried a little earlier to bring up the site and DNS said SERVFAIL. Sigh. Oh well, that site pointed me the in the right direction regarding power supply choices.
- hakfoo 5y ago
  That's a loss. I'm using a Corsair RM1000x basically because it got full marks on his review.
guenthert 5y ago
The description of the regulation of the 3V3 circuit is IMHO misleading. The inductor isn't a magnetic amplifier (multiple coils would be needed), but rather a filter element.
- kens 5y ago
  Are you familiar with the use of magnetic amplifiers to regulate 3.3 V outputs? I traced the circuit and it's a magnetic amplifier. The same winding is used for control and output, as is typical in power supplies.
  - guenthert 5y ago
    No, I am not and had difficulties finding hints. Eventually I found https://www.ti.com/lit/ml/slup129/slup129.pdf https://www.ti.com/lit/ml/slup129/slup129.pdf which I found helpful. "Magnetic Amplifiers Although called a magnetic amplifier; this application really uses an inductive element as a controlled switch. A mag amp is a coil of wire wound on a core with a relatively square B-H characteristic. This gives the coil too operating modes: when unsaturated, the core causes the coil to act as a high inductance capable of supporting a large voltage with little or no current flow. When the core saturates, the impedance of the coil drops to near zero, allowing current to flow with negligible voltage drop. Thus a mag amp comes the closest yet to a true "ideal switch" with significant benefits to switching regulators."
lazyweb 5y ago
> The 60-Hertz AC (alternating current) from the wall oscillates 60 times a second, but the power supply needs steady DC (direct current) that flows in one direction. The full-bridge rectifier [1] below converts the AC to DC. [1] https://www.youtube.com/watch?v=sI5Ftm1-jik https://www.youtube.com/watch?v=sI5Ftm1-jik I just knew which video is linked without clicking. ElectroBOOM is a treasure.
- PhantomGremlin 5y ago
  That guy is "crazy". And yet I learned something. In nearly 50 years of playing with electronics I've never seen such a beautiful LER (light emitting resistor). Edit: I am disappointed in his hooking up his oscilloscope ground to some random point of the circuit. Did he really do that? It sure looked convincing on the video. It's something that everyone using scopes learns not to do very early on. It can't be good for the wiring in the scope.
  - LargoLasskhyfv 5y ago
    My style...likey likey!
  - mastax 5y ago
    Its his style to feign ignorance, do something stupid, then explain what happened. He has a masters degree in electrical engineering and, well, does so much bad stuff that it has to be on purpose.
  - SAI_Peregrinus 5y ago
    Light-emitting bolt: https://i.imgur.com/WxqQIEB.jpeg https://i.imgur.com/WxqQIEB.jpeg Though probably not due to current, likely someone took a torch to it to try to make it easier to remove, and then took a picture. Then again those connections are vastly undersized for the cables...
chmaynard 5y ago
A related article was recently posted on HN: https://spectrum.ieee.org/computing/hardware/a-half-century-ago-better-transistors-and-switching-regulators-revolutionized-the-design-of-computer-power-supplies https://spectrum.ieee.org/computing/hardware/a-half-century-... https://news.ycombinator.com/item?id=27257448 https://news.ycombinator.com/item?id=27257448
jlgaddis 5y ago
I just recently made a nice little 3.3V, 5V, and 12V power supply for my electronics bench using the power supply from an old server. Saved me from buying one and kept the power supply from ending up getting throwed out. "Win-win", as my annoying ex-boss would say.
- Prcmaker 5y ago
  That's exactly what I did for my first benchtop supply. Being a student, 'free' was a pretty good deal. Used it regularly for a good many years until one project I had drew so much current it really accentuated the voltage ripple.
- dhdc 5y ago
  Be careful though, ATX power supplies don't have a crucial feature that bench supplies do: setable current limits. They will pump out as much power as they can to maintain the output voltages until they saturates. Which can result from releasing some magic smoke if you are lucky, to a call with your insurance company.
NelsonMinar 5y ago
I'm still boggling at the way that power is not conducted electrically across the power supply but is instead air-gapped and pass magnetically, via transformers. Isn't that a lot of power?! A modern PC can easily draw 500W or more. Does that mean there's some enormous magnetic field in my power supply? Why doesn't that pose a problem for the things around it? (I cheerfully admit to being very very good at manipulating bits, CPU opcodes, and TCP/IP packets and knowing next to nothing about electrical engineering.)
- coryrc 5y ago
  The magnitude of the magnetic field is small and mostly conducts through the ferrite for maximum efficiency; it's the frequency which allows so much power to be conducted. Also almost nothing in your computer is affected much by moderate magnetic fields. Go ahead, stick magnets all over the motherboard!
- kens 5y ago
  The magnetic field is mostly confined to the core of the transformers, so your power supply isn't going to start attracting things like a giant magnet. This internal field is pretty strong, though, up to 0.3 Tesla in a ferrite core. In comparison, a refrigerator magnet is 5 millitesla and the Earth's magnetic field is 30 microtesla.
- jaidan 5y ago
  That’s how power transformer work in a utility network! We have 120000000w (120MVA) at work. So 500w isn’t much for an isolation transformer.
- nine_k 5y ago
  Air-gapping is a nice side effect, but the real point of using transformers is that they trivially transform voltage. Altering voltage by resistance is enormously wasteful, and can only lower it. Altering voltage by quickly turning it on and off (PWM) only works with certain inert types of load, like electric motors; it works for LEDs only because the inertia of the eye. But this is close enough to AC anyway. Also, the energy of an electromagnetic wave grows as the 4th power of its frequently, IIRC. This is why old power supplies which directly used the 60Hz frequency from the socket were so bulky, while modern power supplies, which convert the mains electricity to high-frequency AC, can use physically small and lightweight transformers.
jhallenworld 5y ago
I had some contact with PSU designers at a name brand server company and learned some things: 1. Electrolytic capacitors: Only Japanese brands can be trusted (this sounds racist or something, but it's an actual requirement). They all should be de-rated for reliability (have 2x the voltage rating). Only exception is the main bulk filter capacitors, where your only reasonable choice is 450V, but these should be 105C. Tantalum capacitors: not allowed. 2. Main switch MOSFETs: only Infineon can be trusted. Single active clamp / single switch topology is a no-no due to bad experience. (I think the one in the article uses a diode clamp, so should be OK). 3. Standby supply needs its own fuse. The problem is that the main fuse is too big for the standby supply. If there is a standby supply fault, you will fill the machine room with smoke and your brand will be mentioned in the news when machine room is shut down. This destroys shareholder value. The current limit for any exposed 12V rail is only 20A or something line that (240VA UL limit), so you must not have exposed 12V when the server cover is open. There was basically a 100 page requirements document all along these lines.
- indigomm 5y ago
  Japanese brands are renowned for having a very reliable electrolyte formula. Dell sourced some capacitors made in Taiwan using a stolen copy of the formulae and it cost them massively. https://www.theguardian.com/technology/blog/2010/jun/29/dell-problems-capacitors https://www.theguardian.com/technology/blog/2010/jun/29/dell...
  - goldcd 5y ago
    Wasn't just Dell - https://en.wikipedia.org/wiki/Capacitor_plague#:~:text=The%20capacitor%20plague%20was%20a,generation%2C%20often%20rupturing%20the%20case https://en.wikipedia.org/wiki/Capacitor_plague#:~:text=The%2... Although even putting this aside, capacitors don't seem to age well - anybody interested in 80s/90s electronics and gaming, will be aware that they should check boards before plugging them in, and if in doubt, but a 're-capping' kit
    - galangalalgol 5y ago
phatty 5y ago
The yellow disk on the primary AC in,is a transient suppressor,not a capacitor.
- kens 5y ago
  Are you referring to the yellow 4.7 nF ceramic Y capacitor, with a capacitor symbol printed on the PCB underneath it?
JKCalhoun 5y ago
As I recall, the Apple II was fairly advanced for having had a switching power supply. I understand in fact it was practically unheard of in consumer electronics. I know the Apple I was a kit and came with no power supply but every one I've ever seen the hobbyist has added a clunky linear power supply with a monster transformer and giant electrolytics. It's almost like the two computers stood so near but just across from one another on two sides of some threshhold.
- ChuckMcM 5y ago
  As I recall, early switching power supplies could not pass FCC Part 15 compliance for home use. This was in part because adding the necessary shielding added cost, and in part because the switching supply was typically more expensive than a gigantic transformer and a linear voltage regulator.
- deleted 5y ago
  [deleted]
- kalleboo 5y ago
  I remember seeing this article on Steve Jobs' claim that the Apple II switching power supply was revolutionary, if anyone wants to read more http://www.righto.com/2012/02/apple-didnt-revolutionize-power.html http://www.righto.com/2012/02/apple-didnt-revolutionize-powe...
young_unixer 5y ago
Isn't there a way to create a rectifier with just three diodes? I remember having come up with a way to make one once, but there must have been something wrong with it (I know nothing about electronics). Now I can't remember how it was, or maybe it had 4 and just looked slightly different from the typical one.
- unnouinceput 5y ago
  Yes, there is. 3 diodes and 3 capacitors. But the catch is that the output is going to be 930 Vcc instead of just 310 Vcc. It's called Vcc multiplier and you can easily reach thousands of volts this way - that's how the police teasers work, they have a small DC to AC converter and then use this kind of multiplier to shock people by driving 25K Vcc, but the intensity is around 10 nA (if it would be 1 mA the teaser would kill instantly). https://www.electronicshub.org/wp-content/uploads/2017/04/Voltage-Tripler-Circuit-1024x431.jpg https://www.electronicshub.org/wp-content/uploads/2017/04/Vo...
  - AndresNavarro 5y ago
    Ah, totally forgot about these. My father saw them extensively in x-ray generators (which may reach over 100KV for some applications...)
- AndresNavarro 5y ago
  As a matter of fact you can do it with just one... That would be a half wave rectifier (not that good, you miss half the cycle). You can also do full wave with just two, but you need a center tap on your transformer. I remember finding both of these in early guitar tube amplifiers schematics (those early ones used vacuum tubes for everything: rectification, pre-amp & power).
SavantIdiot 5y ago
Nicely written up. It's not that complicated when you start to think about the different stages, and I think this walk-through breaks it up clearly. If you continue further on to the motherboard, the CPU has a multiphase SMPS (sometimes exceeding 20 phases!) that drops the voltage further to core and IO voltages (usally ~1.8V or less for the former) but still has to generate lots of Watts (think about a Xeon or Ryzen at 3+ GHz). What's really neat IMHO is how Apple changed the <5W adapter market by moving to dense SMP in such a brilliant form factor. It can take 120/240 because it is a buck converter and doesn't care about the input voltage. I've wondered, if the SMPS circuit in the 5W apple adapters be scaled up to 600~800W would they be enormous and/or less efficient? Because it seems like the circuits in this board are either designed for higher power so big honkin' coils & caps are necessary, or are they that big (and inefficient) in order to save money?
- mastax 5y ago
  > I've wondered, if the SMPS circuit in the 5W apple adapters be scaled up to 600~800W would they be enormous and/or less efficient? Because it seems like the circuits in this board are either designed for higher power so big honkin' coils & caps are necessary, or are they that big (and inefficient) in order to save money? All power supplies of a few hundred watts will look broadly the same as this one. The rare exceptions are very expensive AC/DC modules[0], and linear power supplies used mostly in higher-end audio and test equipment. There are a number of factors that influence the designs that are practical for different power outputs but a big one is the gate charge of the switching transistor. Bigger output power requires a bigger switching transistor which stores more charge in its gate. This requires more energy from the controller to charge and discharge the gate and more concern about the ohmic losses in the transistor as its transitioning from being on to being off. This limits the switching frequency you can practically use. Lower switching frequency means larger transformer; you need more iron to take the magnetic field so it doesn't saturate on the larger slower pulses. Note also that with more power almost every component needs to be larger. Also note that standard PC supplies need to supply many voltage rails while the classic Apple 5W adapter only needs one. With newer standards like ATX12VO the supply only supplies 12V and 12V standby. [0]: http://www.vicorpower.com/ac-dc/converters/ac-front-end-module http://www.vicorpower.com/ac-dc/converters/ac-front-end-modu... [1]: https://audiobacon.net/2018/06/29/linear-power-supplies-for-audiophiles-getting-closer-to-live/ https://audiobacon.net/2018/06/29/linear-power-supplies-for-...
Stratoscope 5y ago
Lenovo has done something interesting in recent generations of laptop power supplies that made them a lot smaller and lighter. The 170W power supply for my old ThinkPad W520 measures about 17cm x 8cm x 3cm and weighs about 580g. The 170W supply for my new X1 Extreme measures about 14cm x 8cm x 2cm and weighs about 320g. Does anyone know what technology let them make the power supply so much smaller and lighter?
- foodstances 5y ago
  Probably GaN
  - Stratoscope 5y ago
    Oh, thank you. Very interesting, that is exactly what it is: https://www.google.com/search?q=lenovo+charger+gan https://www.google.com/search?q=lenovo+charger+gan
  - rcxdude 5y ago
    Exactly. GaN FETs are slowly taking hold of the market, due to their ridiculous performance capabilities (mainly being able to switch much faster than silicon for the same losses). I think there was a car manufacturer who reckons there would eventually not be any silicon power transistors in their vehicles, they would all be either GaN (for lower voltages) or SiC (for higher voltages).
- userbinator 5y ago
  I would suspect that it is simply the subtle art of pushing components closer to their limits... since a laptop is unlikely to be drawing 170W continuously, they may be using PSUs with the same peak ratings but at a lower duty cycle.[1] (Note that Lenovo itself almost certainly doesn't design nor produce them -- if there's a UL registration number or similar, you may be able to find the actual OEM/ODM.) [1] You can see something similar in the marketing specs for cars vs. trucks - a performance car may have a 2L engine rated for 300HP, while you can find a truck with a 9L engine also rated at 300HP. The former is unlikely to last for long putting out its rated power.
xx789 5y ago
Often PSUs will have different wattage sets but seem otherwise identical eg 550/650. Are they binned like CPUs? Or are there higher rated components
rex_lupi 5y ago
DiodeGoneWild (danyk.cz) has a bunch of very good and in-depth videos on these: How Does a Computer Power Supply Work (ATX): https://www.youtube.com/watch?v=Cur3nQjjyyo https://www.youtube.com/watch?v=Cur3nQjjyyo How To Repair a Computer Power Supply (or other switching power supply): https://www.youtube.com/watch?v=HcYFbCqM61g https://www.youtube.com/watch?v=HcYFbCqM61g
puzzlingcaptcha 5y ago
I'm glad to see Ken's blog on HN. He does incredible stuff with reverse-engineering old proprietary chips, e.g. the HP nanoprocessor which he reverse-engineered from masks then wrote a disassembler for. https://en.wikipedia.org/wiki/Hewlett-Packard_Nanoprocessor https://en.wikipedia.org/wiki/Hewlett-Packard_Nanoprocessor http://www.righto.com/2020/09/hp-nanoprocessor-part-ii-reverse.html http://www.righto.com/2020/09/hp-nanoprocessor-part-ii-rever...

407 points by parsecs 5y ago

If anyone wants to see a really top quality PC power supply, for comparison to a cheap one, take a look at the board and layout on a $100 seasonic power supply. Well known Taiwanese power supply company that doesn't try to compete on cheap prices and has been around for 20+ years.

ta988 5y ago
http://www.kitguru.net/wp-content/uploads/2014/08/DSCF2160.jpg http://www.kitguru.net/wp-content/uploads/2014/08/DSCF2160.j...
- judge2020 5y ago
  They use hotlink protection to prevent other sites from embedding their images - you'll have to view that image from https://www.kitguru.net/components/power-supplies/zardon/seasonic-x-series-1050w-power-supply-ss-1050xm2/5/ https://www.kitguru.net/components/power-supplies/zardon/sea... or open it in a new tab.
  - ta988 5y ago
    Oh sorry, I didn't realize that.

amelius 5y ago

It would be nice if the article showed some voltage or current plots for various places in the circuit.

robbmorganf 5y ago

I never realized the main transformer element worked on rectified AC. Could someone explain why we rectify the AC power before the transformer? I always thought transformers worked on AC power anyways.

cristoperb 5y ago
In switching mode power supplies like this, the mains AC is rectified and then chopped up into higher frequency pulses and fed to the transformer. The higher frequency allows for smaller transformer. It also allows for voltage regulation because the input pulse width (in this case via the UC3842B controller IC) can be altered based on the sensed output voltage.
RL_Quine 5y ago
50/60hz requires a large transformer core. Switching power supplies rectify to DC, then drive the transformer at potentially megahertz which increases efficiency and substantially reduces the size and weight of the core. For similar reasons aircraft use 400hz 115v supply as it makes all of the power conversion electronics dramatically smaller.
- londons_explore 5y ago
  To add to this... A transformer converts electrical energy into a magnetic field and back into electrical energy. All the energy from a single 'sine wave' must be stored in the magnetic field inside the transformer briefly before coming out of the output. The transformer core is made of steel usually. For a given weight of steel, there is a maximum amount of magnetic energy it can store. That means that at low frequencies like 50/60Hz, transformers end up very bulky.
  - whoisburbansky 5y ago
    Wasn’t immediately clear from GPs comment and my admittedly limited physics instruction, but the way you explained it made it seem incredibly obvious in retrospect, which is a rare skill, thanks!
- jeffbee 5y ago
  The standing field in a massive 60Hz transformer also necessitates robust inrush protection. With a transformer across the mains, losing the input power momentarily can cause a huge surge current when the input is reapplied. With the bridge and filter first, the inrush from being momentarily switched off won't be severe.

marcodiego 5y ago

I generally think of a switching power supply as a PWM damped by a capacitor. Never knew exactly how oversimplified my thinking is.

amelius 5y ago
The problem with this view is that a capacitor at a low impedance output will do nothing.
- marcodiego 5y ago
  Hmmm... makes sense. Is it possible to ELI5 what should be put after the PWM so it can handle low impedancies? From https://www.electronics-tutorials.ws/power/switch-mode-power-supply.html https://www.electronics-tutorials.ws/power/switch-mode-power... "The Buck Switching Regulator" looks like an arrangement with a diode, inductor and capacitor is enough. Interesting.
  - amelius 5y ago
    The link you found explains it well, but there is a different perspective if you want to focus on impedances. The idea is to drive the capacitor with a high impedance. This impedance should not be a resistor, because a resistor will limit current (more current means a higher voltage drop in the output), further it will consume power and become hot. Instead, you should look for something that works more like an ideal current source. An ideal current source has an infinite output impedance (because loosely speaking the impedance R=dv/di and di=0 for an ideal current source). A constant current source is a good fit for charging a capacitor since a constant current means a constant dv/dt slope. Now, as your link shows, a switching power supply does not have a constant current source in its main circuit, but it does use an inductor which has similar characteristics since inductors resist changes in current. The governing equation of an inductor is v=L*di/dt, and for the output impedance of the inductor you get loosely speaking R=dv/di =L/dt, which is large for large L and short timescales (dt close to 0), hence the similarity to an ideal current source. Now the driving part of the circuit at the left of the schematics in your link is a voltage source. So to drive an inductor, you use a voltage source. And to drive a capacitor, you use a current source. Inductors can be seen as current sources, and capacitors can be seen as voltage sources. I hope this explains it.

Scene_Cast2 5y ago

I wonder where the losses are, and if GaN power transistors for switching would help with efficiency here. I like Seasonic's fanless series, but wouldn't mind getting a bit more power out of the same size PSU.

londons_explore 5y ago
There are losses in every step, and power supply design is basically a big optimization problem to choose all the design parameters to minimize losses. The main components with losses: * The input capacitors are non-ideal and have some resistance. That resistance causes heat every time current flows in or out of them. * The MOSFET switch has an 'on resistance' which means it wastes energy when current flows through it. * The MOSFET takes a certain time to turn on or off. During that time it is partially on, which wastes a bunch of energy each switch. * The transformer has resistance in the coils. * The transformer has iron core hysteresis, which makes the steel of the transformer get warm as magnetic fields change in it. * The diode on the output side has voltage drop across it. * The capacitor on the output side has resistance.
- quercusa 5y ago
  It was a real learning experience moving from ideal transistors to real MOSFETs in an H-bridge driving a motor. Gate capacitance led to lots of expensive smokefests.
R0b0t1 5y ago
They do help. Since HN finds it interesting I can write some on the most modern designs. I am currently designing a FOSS power supply. One of the goals is to go for high efficiency. The end product will use GaN and SiC elements. The different chemistries give different switching characteristics. (Interesting aside is that some topologies can run forward as line conditioning AND backwards as a motor inverter.) There are also supply chain and security considerations, though. You can buy magic PSU chips but what if you can't?
- Scene_Cast2 5y ago

Gys 5y ago

I am pleasantly suprised this does not have its own internet connected microcontroller. So at least one element that is still not hackable.

BenjiWiebe 5y ago
Internet connected microcontrollers weren't very common in 2005.
- Gys 5y ago
  Ai, missed that part! Thanks.

londons_explore 5y ago

Bear in mind this is a very old power supply. A modern supply would use the same principles, but would probably have mostly surface mount components, a single controller IC, and probably separate switching supplies for each different supplied voltage.

kens 5y ago
The power supply is from 2005. By my standards that's not very old, but maybe because I've also been looking at power supplies from the 1940s :-) Specifically a 100-pound Teletype power supply from the Navy that used mercury-vapor thyratron tubes. http://www.righto.com/2018/09/glowing-mercury-thyratrons-inside-1940s.html http://www.righto.com/2018/09/glowing-mercury-thyratrons-ins...
- quercusa 5y ago
  Two great articles, Ken!
dfox 5y ago
Last time I looked at it it was not especially cost effective to build PC power supplies on multilayer boards. That leads to exactly the kind of construction as in this power supply: large almost completely through hole single-sided board with power components and one or more higher density perpendicular sub-boards with control logic.
- londons_explore 5y ago
  2 layer boards with smd components are now cheaper than single layer and through hole - simply because through hole requires more labour to place components and has a substantially higher failure rate (bad joints). Obviously some components in a power supply still need to be through hole for mechanical reasons, but it isn't many.
  - dfox 5y ago
    It is not that clear-cut. Obviously the optimal case is SMD-only, but there is a threshold when THT-only becomes cheaper than SMD/THT mix. Another thing is that power supplies tend to use higher temperature board material (presumably to allow for thinner copper plating) which is somewhat rare and expensive in dual layer configurations.

janci 5y ago

Server power supplies are impressive. I pulled out some PSUs from old scrapped servers. In a smaller form factor than ATX they deliver more than 1kW power. You read that right. 100A at 12V actually.

snypher 5y ago
100A over how many 12V circuits? I doubt it is just a single circuit, or you would need a ~4AWG cable and rated connector?
- ptomato 5y ago
  from the PSU typically one (on hotswap supplies); e.g. on https://cdn11.bigcommerce.com/s-qfzamxn9kz/images/stencil/original/products/130535/437709/570451-001-2__86092.1579103875.jpg?c=2 https://cdn11.bigcommerce.com/s-qfzamxn9kz/images/stencil/or... the connectors on the left are just control/sense pins and the big beefy ones are a single 12v & ground.
- namibj 5y ago
  They plug in via an edge connector straight into the mother board, or sometimes into a separate board that connects to the mother board.
- deleted 5y ago
  [deleted]
LargoLasskhyfv 5y ago
Only if you are deaf. Otherwise they are annoyingly loud. Whhhhsssssssss

flyinghamster 5y ago

The real treats were the bottom-of-the-barrel PSUs. I remember having to deal with a slew of these at work back in the early aughts. I remember turning on a machine one day... sssFWSSSSSSSHH and the magic smoke came pouring out. It would up taking out the the motherboard and hard drive with it. I autopsied the dead power supply, and it was chock full of capacitors (some blown-out) marked "Rulycon" (note, not Rubycon).

LargoLasskhyfv 5y ago
Name is program. Rulers of con ;->

nickpeterson 5y ago

Just an observation from years building computers. Never cheap out on power supplies. Always buy one (don't use one included in a case), and buy one rated 25-30% above what you think you'll need. Some of the most aggravating troubleshooting you'll ever endure can be avoided entirely.

monocasa 5y ago
Towards that end does anyone know if there any ATX power supplies that will stream out their sensor info over a serial port or something? It'd be nice to have power monitoring on that side of the mainboard's power regulators and caps, to pick up marginal issues before they get filtered out, and the power supplies these days will have a little ucontroller with all that information anyway without the mainboard having to duplicate that monitoring circuitry in the right place. For what's such an important piece of a computer there's so little introspection for data while in use that has to be being collected regardless. Yeah, you can always hook up a oscope or what have you, but catching it in the act of being marginal early on would have saved me more hours in my life than I'd like to admit.
- daper 5y ago
  Server PSUs support such communication (looks like this is PMBus protocol, variation of SMBus, which is variation of I²C). In servers it's connected to the BCM and usually allows to read input and output power, FAN speed, temperatures and status (good/bad). The BCM often records historical data, including peak power (in last 1h, 24h), etc. After quick searching is looks there are people reading this info with a MCU [1]. But I think it would be hard to find such PSU in ATX form factor. [1] https://github.com/sxjack/dps750tb_psu_i2c https://github.com/sxjack/dps750tb_psu_i2c
- dendriti 5y ago
  Whenever I experience issues which are likely related to a power supply, it is much easier to drop in a known-good replacement than to spend time diagnosing the specific issues. Also better to remove a potentially faulty PSU before it damages much more expensive hardware.

cesarb 5y ago

> The secondary circuitry produces the four output voltages: 5 volts, 12 volts, -12 volts, and 3.3 volts. [...] The power supply also provides a negative voltage output (-12 V). This voltage is mostly obsolete, but was used to power serial ports and PCI slots. And even older PC power supplies also provided a -5V voltage, the corresponding pin on the ATX connector is now (according to Wikipedia) a reserved pin. This progression also shows in the expansion slot standards: the ISA slot had pins for -5V and -12V; the PCI slot removed the -5V pin; and the PCIe slot finally removed the -12V pin. That is, a motherboard without any ISA or PCI slot, and without a RS232 socket or header, has no use for the -12V voltage. And there's already a newer power supply standard, called ATX12VO, which simplifies the power supply by providing only 12V (and a separate standby 12V). There's already at least one motherboard built for that standard: https://www.anandtech.com/show/15763/first-atx12vo-consumer-motherboard-the-asrock-z490-phantom-gaming-4sr https://www.anandtech.com/show/15763/first-atx12vo-consumer-...

bruce343434 5y ago
> -12v, -5v What prevents one from just wiring mobo.5v to port.gnd and mobo.gnd to port.-5v? That would effectively create a -5v potential between port.gnd and port.-5v
- formerly_proven 5y ago
  -12 V was used for RS-232, which uses +12 V and -12 V levels (with a very wide tolerance band). Having a separate supply for this was a design decision which was pretty much instantly obsolete with integrated charge pumps: All RS-232 outputs are running off of charge pumps running at (-2) and (+2) ratios, so +-10 V levels with a 5 V supply. I don't know what -5 V was used for. Maybe some analog circuits somewhere, very early MOS logic also often had awkward supply voltages (charge-pumps made this obsolete too, just like high-voltage supplies for EEPROMs).
  - kens 5y ago
    Early DRAM chips like the MK4116 required -5 V, +5 V, and +12 V. (-5 was the substrate back bias for the chip.) So the ISA standard required -12 V, -5 V, +5 V, and +12 V.

Animats 5y ago

Some components, mostly capacitors, have the wrong hole spacing for their pins, and leads were bent to fit. That suggests part substitutions during assembly. Many of the through-hole components were not pushed all the way down into the board. That suggests overworked assemblers. This was obviously hand-assembled. The author makes a point that there's a clear division between the AC line side and the DC side. That's required for UL approval, but power supplies do show up without it. The power transformer that crosses the boundary should also have a split bobbin, so the AC line side coil and the output side coil are separated by a barrier, not wound on the same bobbin. There are worse power supplies.[1] [1] https://linustechtips.com/topic/515473-teardown-and-review-of-the-turbolink-atx-xg500w-crappy-psu/ https://linustechtips.com/topic/515473-teardown-and-review-o...

lmilcin 5y ago
> The power transformer that crosses the boundary should also have a split bobbin, so the AC line side coil and the output side coil are separated by a barrier, not wound on the same bobbin. Separate bobbin is not required for robust isolation. For example, just right now on my bench there is a medical separation transformer. No separate bobbin (hint: it is toroidal).
formerly_proven 5y ago
I have never seen a split bobbin in an ATX supply — they are bad for efficiency.
GekkePrutser 5y ago
There's worse power supplies sure but this one is still a mess. I don't see anything obviously dangerous but it's still a dirty ugly design and assembly. Other companies like Delta Electronics manage to cram lots of components in small spaces too but they actually do a good, clean job. Most PCBs with large, heavy through-hole components are still manufactured by hand, by the way.
- deleted 5y ago
  [deleted]
- 5y ago

bonoboTP 5y ago

Even if you're a "computer person" who is comfortable messing with the internals of a PC, be very careful with the power supply. Opening it up should really be left to professionals. Capacitors can remain charged for a long time after disconnecting the power cord. If despite all the warnings, you open it up to fiddle with internals because you think you understand the components and can pay attention not to touch things, at the very least, use only one hand at a time to avoid creating a circuit through your heart. In most other parts of the computer the worst that can happen in most cases is that you damage the computer, the power supply is different, there you also have a good chance of getting shocked.

parsecs 5y ago
Also a good tip to touch things with the back of your hand first, as the current can't force you to grip harder. This is more for line connected stuff though.
- LambdaComplex 5y ago
  An even better tip would be to use an insulated screwdriver instead of your hand. Or even a capacitor discharge tool, since those apparently exist.
  - Scoundreller 5y ago
    When I had to do an air conditioning capacitor, I used a piece of wood with a nail. I couldn’t tell if adding steel wool to the mix would be a good idea or not.
    - baud147258 5y ago
      Wouldn't steel wool catch fire when exposed to an electric current? It might be useful to indicate there was still some charge in the capacitors, though
      - Scoundreller 5y ago

lini 5y ago

ATX12VO[1] is a proposed major change to PSUs that hopefully will come in the near future. It will mean simpler (cheaper) designs and improved efficiency. I hope that the DIY market adopts ATX12VO before my next upgrade. Currently only OEMs have the ability build PCs with these kinds of PSUs. [1] https://www.intel.com/content/dam/www/public/us/en/documents/guides/single-rail-power-supply-platform-atx12vo-design-guide.pdf https://www.intel.com/content/dam/www/public/us/en/documents...

dhdc 5y ago
...which puts all the DC conversion on the motherboard. Honestly, I can't tell if this is a good thing or a bad thing. On the plus side, power supplies will be much simpler to design and test, with potentially better efficiencies. On the other hand, all those additional DC-DC converters will take up quite a bit of space on the already crammed boards, and now you got more heat to manage.
- agumonkey 5y ago
  fair point
- formerly_proven 5y ago
  It recognizes how things are already. The 5 V and 3.3 V step-down converters in the PSU are pretty much only for Molex/SATA-connected peripherals, and those don't use 3.3 V anyway (99.5 % of them), since it's not guaranteed to be there. So the 3.3 V rail is pretty much pointless. 5 V not quite as much, but even in an enthusiast-level PC there will be probably just a handful of things actually connected to that - most likely SSD/HDD and maybe something like a fan controller. No heavy loads are connected to the 5 V / 3.3 V rails. Those are all supplied through the 12 V rail.
  - dhdc 5y ago
    I am pretty sure M.2 uses 3.3V exclusively, and depending on the implementation, RAM sometimes gets its power from down regulated 3.3V as well. Though you do have a good point, nobody misses -12V and -5V.

celim307 5y ago

On a somewhat related note, I just found out johnnyguru, a major contributor to consumer psu reviews and knowledge, has shut down his site and forums. His tear downs were always fascinating https://web.archive.org/web/20210126113732/http://www.jonnyguru.com/forums/archive/index.php/t-16610.html https://web.archive.org/web/20210126113732/http://www.jonnyg...

45ure 5y ago
Some accrued knowledge still survives, within a community, which is trying to keep it alive. I wish them all the luck. http://www.johnnylucky.org/power-supplies/psu-recommendations.html http://www.johnnylucky.org/power-supplies/psu-recommendation... https://hardforum.com/forums/power-supplies.93/ https://hardforum.com/forums/power-supplies.93/
PragmaticPulp 5y ago
The computer enthusiast market is a difficult niche to cater to online. Most of the visitors will arrive with ad blockers enabled and they’re going to buy products from the cheapest retailer directly, not through affiliate links. Also, some of them will be brutally combative for no particular reason. The originator of that website landed a dream job doing R&D for Corsair. The owner of the domain (not Johnny, as far as I can tell) simply decided to let it expire.
flyinghamster 5y ago
I tried a little earlier to bring up the site and DNS said SERVFAIL. Sigh. Oh well, that site pointed me the in the right direction regarding power supply choices.
hakfoo 5y ago
That's a loss. I'm using a Corsair RM1000x basically because it got full marks on his review.

guenthert 5y ago

The description of the regulation of the 3V3 circuit is IMHO misleading. The inductor isn't a magnetic amplifier (multiple coils would be needed), but rather a filter element.

kens 5y ago
Are you familiar with the use of magnetic amplifiers to regulate 3.3 V outputs? I traced the circuit and it's a magnetic amplifier. The same winding is used for control and output, as is typical in power supplies.
- guenthert 5y ago
  No, I am not and had difficulties finding hints. Eventually I found https://www.ti.com/lit/ml/slup129/slup129.pdf https://www.ti.com/lit/ml/slup129/slup129.pdf which I found helpful. "Magnetic Amplifiers Although called a magnetic amplifier; this application really uses an inductive element as a controlled switch. A mag amp is a coil of wire wound on a core with a relatively square B-H characteristic. This gives the coil too operating modes: when unsaturated, the core causes the coil to act as a high inductance capable of supporting a large voltage with little or no current flow. When the core saturates, the impedance of the coil drops to near zero, allowing current to flow with negligible voltage drop. Thus a mag amp comes the closest yet to a true "ideal switch" with significant benefits to switching regulators."

lazyweb 5y ago

> The 60-Hertz AC (alternating current) from the wall oscillates 60 times a second, but the power supply needs steady DC (direct current) that flows in one direction. The full-bridge rectifier [1] below converts the AC to DC. [1] https://www.youtube.com/watch?v=sI5Ftm1-jik https://www.youtube.com/watch?v=sI5Ftm1-jik I just knew which video is linked without clicking. ElectroBOOM is a treasure.

PhantomGremlin 5y ago
That guy is "crazy". And yet I learned something. In nearly 50 years of playing with electronics I've never seen such a beautiful LER (light emitting resistor). Edit: I am disappointed in his hooking up his oscilloscope ground to some random point of the circuit. Did he really do that? It sure looked convincing on the video. It's something that everyone using scopes learns not to do very early on. It can't be good for the wiring in the scope.
- LargoLasskhyfv 5y ago
  My style...likey likey!
- mastax 5y ago
  Its his style to feign ignorance, do something stupid, then explain what happened. He has a masters degree in electrical engineering and, well, does so much bad stuff that it has to be on purpose.
- SAI_Peregrinus 5y ago
  Light-emitting bolt: https://i.imgur.com/WxqQIEB.jpeg https://i.imgur.com/WxqQIEB.jpeg Though probably not due to current, likely someone took a torch to it to try to make it easier to remove, and then took a picture. Then again those connections are vastly undersized for the cables...

chmaynard 5y ago

A related article was recently posted on HN: https://spectrum.ieee.org/computing/hardware/a-half-century-ago-better-transistors-and-switching-regulators-revolutionized-the-design-of-computer-power-supplies https://spectrum.ieee.org/computing/hardware/a-half-century-... https://news.ycombinator.com/item?id=27257448 https://news.ycombinator.com/item?id=27257448

jlgaddis 5y ago

I just recently made a nice little 3.3V, 5V, and 12V power supply for my electronics bench using the power supply from an old server. Saved me from buying one and kept the power supply from ending up getting throwed out. "Win-win", as my annoying ex-boss would say.

Prcmaker 5y ago
That's exactly what I did for my first benchtop supply. Being a student, 'free' was a pretty good deal. Used it regularly for a good many years until one project I had drew so much current it really accentuated the voltage ripple.
dhdc 5y ago
Be careful though, ATX power supplies don't have a crucial feature that bench supplies do: setable current limits. They will pump out as much power as they can to maintain the output voltages until they saturates. Which can result from releasing some magic smoke if you are lucky, to a call with your insurance company.

NelsonMinar 5y ago

I'm still boggling at the way that power is not conducted electrically across the power supply but is instead air-gapped and pass magnetically, via transformers. Isn't that a lot of power?! A modern PC can easily draw 500W or more. Does that mean there's some enormous magnetic field in my power supply? Why doesn't that pose a problem for the things around it? (I cheerfully admit to being very very good at manipulating bits, CPU opcodes, and TCP/IP packets and knowing next to nothing about electrical engineering.)

coryrc 5y ago
The magnitude of the magnetic field is small and mostly conducts through the ferrite for maximum efficiency; it's the frequency which allows so much power to be conducted. Also almost nothing in your computer is affected much by moderate magnetic fields. Go ahead, stick magnets all over the motherboard!
kens 5y ago
The magnetic field is mostly confined to the core of the transformers, so your power supply isn't going to start attracting things like a giant magnet. This internal field is pretty strong, though, up to 0.3 Tesla in a ferrite core. In comparison, a refrigerator magnet is 5 millitesla and the Earth's magnetic field is 30 microtesla.
jaidan 5y ago
That’s how power transformer work in a utility network! We have 120000000w (120MVA) at work. So 500w isn’t much for an isolation transformer.
nine_k 5y ago
Air-gapping is a nice side effect, but the real point of using transformers is that they trivially transform voltage. Altering voltage by resistance is enormously wasteful, and can only lower it. Altering voltage by quickly turning it on and off (PWM) only works with certain inert types of load, like electric motors; it works for LEDs only because the inertia of the eye. But this is close enough to AC anyway. Also, the energy of an electromagnetic wave grows as the 4th power of its frequently, IIRC. This is why old power supplies which directly used the 60Hz frequency from the socket were so bulky, while modern power supplies, which convert the mains electricity to high-frequency AC, can use physically small and lightweight transformers.

jhallenworld 5y ago

I had some contact with PSU designers at a name brand server company and learned some things: 1. Electrolytic capacitors: Only Japanese brands can be trusted (this sounds racist or something, but it's an actual requirement). They all should be de-rated for reliability (have 2x the voltage rating). Only exception is the main bulk filter capacitors, where your only reasonable choice is 450V, but these should be 105C. Tantalum capacitors: not allowed. 2. Main switch MOSFETs: only Infineon can be trusted. Single active clamp / single switch topology is a no-no due to bad experience. (I think the one in the article uses a diode clamp, so should be OK). 3. Standby supply needs its own fuse. The problem is that the main fuse is too big for the standby supply. If there is a standby supply fault, you will fill the machine room with smoke and your brand will be mentioned in the news when machine room is shut down. This destroys shareholder value. The current limit for any exposed 12V rail is only 20A or something line that (240VA UL limit), so you must not have exposed 12V when the server cover is open. There was basically a 100 page requirements document all along these lines.

indigomm 5y ago
Japanese brands are renowned for having a very reliable electrolyte formula. Dell sourced some capacitors made in Taiwan using a stolen copy of the formulae and it cost them massively. https://www.theguardian.com/technology/blog/2010/jun/29/dell-problems-capacitors https://www.theguardian.com/technology/blog/2010/jun/29/dell...
- goldcd 5y ago
  Wasn't just Dell - https://en.wikipedia.org/wiki/Capacitor_plague#:~:text=The%20capacitor%20plague%20was%20a,generation%2C%20often%20rupturing%20the%20case https://en.wikipedia.org/wiki/Capacitor_plague#:~:text=The%2... Although even putting this aside, capacitors don't seem to age well - anybody interested in 80s/90s electronics and gaming, will be aware that they should check boards before plugging them in, and if in doubt, but a 're-capping' kit
  - galangalalgol 5y ago

phatty 5y ago

The yellow disk on the primary AC in,is a transient suppressor,not a capacitor.

kens 5y ago
Are you referring to the yellow 4.7 nF ceramic Y capacitor, with a capacitor symbol printed on the PCB underneath it?

JKCalhoun 5y ago

As I recall, the Apple II was fairly advanced for having had a switching power supply. I understand in fact it was practically unheard of in consumer electronics. I know the Apple I was a kit and came with no power supply but every one I've ever seen the hobbyist has added a clunky linear power supply with a monster transformer and giant electrolytics. It's almost like the two computers stood so near but just across from one another on two sides of some threshhold.

ChuckMcM 5y ago
As I recall, early switching power supplies could not pass FCC Part 15 compliance for home use. This was in part because adding the necessary shielding added cost, and in part because the switching supply was typically more expensive than a gigantic transformer and a linear voltage regulator.
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kalleboo 5y ago
I remember seeing this article on Steve Jobs' claim that the Apple II switching power supply was revolutionary, if anyone wants to read more http://www.righto.com/2012/02/apple-didnt-revolutionize-power.html http://www.righto.com/2012/02/apple-didnt-revolutionize-powe...

young_unixer 5y ago

Isn't there a way to create a rectifier with just three diodes? I remember having come up with a way to make one once, but there must have been something wrong with it (I know nothing about electronics). Now I can't remember how it was, or maybe it had 4 and just looked slightly different from the typical one.

unnouinceput 5y ago
Yes, there is. 3 diodes and 3 capacitors. But the catch is that the output is going to be 930 Vcc instead of just 310 Vcc. It's called Vcc multiplier and you can easily reach thousands of volts this way - that's how the police teasers work, they have a small DC to AC converter and then use this kind of multiplier to shock people by driving 25K Vcc, but the intensity is around 10 nA (if it would be 1 mA the teaser would kill instantly). https://www.electronicshub.org/wp-content/uploads/2017/04/Voltage-Tripler-Circuit-1024x431.jpg https://www.electronicshub.org/wp-content/uploads/2017/04/Vo...
- AndresNavarro 5y ago
  Ah, totally forgot about these. My father saw them extensively in x-ray generators (which may reach over 100KV for some applications...)
AndresNavarro 5y ago
As a matter of fact you can do it with just one... That would be a half wave rectifier (not that good, you miss half the cycle). You can also do full wave with just two, but you need a center tap on your transformer. I remember finding both of these in early guitar tube amplifiers schematics (those early ones used vacuum tubes for everything: rectification, pre-amp & power).

SavantIdiot 5y ago

Nicely written up. It's not that complicated when you start to think about the different stages, and I think this walk-through breaks it up clearly. If you continue further on to the motherboard, the CPU has a multiphase SMPS (sometimes exceeding 20 phases!) that drops the voltage further to core and IO voltages (usally ~1.8V or less for the former) but still has to generate lots of Watts (think about a Xeon or Ryzen at 3+ GHz). What's really neat IMHO is how Apple changed the <5W adapter market by moving to dense SMP in such a brilliant form factor. It can take 120/240 because it is a buck converter and doesn't care about the input voltage. I've wondered, if the SMPS circuit in the 5W apple adapters be scaled up to 600~800W would they be enormous and/or less efficient? Because it seems like the circuits in this board are either designed for higher power so big honkin' coils & caps are necessary, or are they that big (and inefficient) in order to save money?

mastax 5y ago
> I've wondered, if the SMPS circuit in the 5W apple adapters be scaled up to 600~800W would they be enormous and/or less efficient? Because it seems like the circuits in this board are either designed for higher power so big honkin' coils & caps are necessary, or are they that big (and inefficient) in order to save money? All power supplies of a few hundred watts will look broadly the same as this one. The rare exceptions are very expensive AC/DC modules[0], and linear power supplies used mostly in higher-end audio and test equipment. There are a number of factors that influence the designs that are practical for different power outputs but a big one is the gate charge of the switching transistor. Bigger output power requires a bigger switching transistor which stores more charge in its gate. This requires more energy from the controller to charge and discharge the gate and more concern about the ohmic losses in the transistor as its transitioning from being on to being off. This limits the switching frequency you can practically use. Lower switching frequency means larger transformer; you need more iron to take the magnetic field so it doesn't saturate on the larger slower pulses. Note also that with more power almost every component needs to be larger. Also note that standard PC supplies need to supply many voltage rails while the classic Apple 5W adapter only needs one. With newer standards like ATX12VO the supply only supplies 12V and 12V standby. [0]: http://www.vicorpower.com/ac-dc/converters/ac-front-end-module http://www.vicorpower.com/ac-dc/converters/ac-front-end-modu... [1]: https://audiobacon.net/2018/06/29/linear-power-supplies-for-audiophiles-getting-closer-to-live/ https://audiobacon.net/2018/06/29/linear-power-supplies-for-...

Stratoscope 5y ago

Lenovo has done something interesting in recent generations of laptop power supplies that made them a lot smaller and lighter. The 170W power supply for my old ThinkPad W520 measures about 17cm x 8cm x 3cm and weighs about 580g. The 170W supply for my new X1 Extreme measures about 14cm x 8cm x 2cm and weighs about 320g. Does anyone know what technology let them make the power supply so much smaller and lighter?

foodstances 5y ago
Probably GaN
- Stratoscope 5y ago
  Oh, thank you. Very interesting, that is exactly what it is: https://www.google.com/search?q=lenovo+charger+gan https://www.google.com/search?q=lenovo+charger+gan
- rcxdude 5y ago
  Exactly. GaN FETs are slowly taking hold of the market, due to their ridiculous performance capabilities (mainly being able to switch much faster than silicon for the same losses). I think there was a car manufacturer who reckons there would eventually not be any silicon power transistors in their vehicles, they would all be either GaN (for lower voltages) or SiC (for higher voltages).
userbinator 5y ago
I would suspect that it is simply the subtle art of pushing components closer to their limits... since a laptop is unlikely to be drawing 170W continuously, they may be using PSUs with the same peak ratings but at a lower duty cycle.[1] (Note that Lenovo itself almost certainly doesn't design nor produce them -- if there's a UL registration number or similar, you may be able to find the actual OEM/ODM.) [1] You can see something similar in the marketing specs for cars vs. trucks - a performance car may have a 2L engine rated for 300HP, while you can find a truck with a 9L engine also rated at 300HP. The former is unlikely to last for long putting out its rated power.

xx789 5y ago

Often PSUs will have different wattage sets but seem otherwise identical eg 550/650. Are they binned like CPUs? Or are there higher rated components

rex_lupi 5y ago

DiodeGoneWild (danyk.cz) has a bunch of very good and in-depth videos on these: How Does a Computer Power Supply Work (ATX): https://www.youtube.com/watch?v=Cur3nQjjyyo https://www.youtube.com/watch?v=Cur3nQjjyyo How To Repair a Computer Power Supply (or other switching power supply): https://www.youtube.com/watch?v=HcYFbCqM61g https://www.youtube.com/watch?v=HcYFbCqM61g

puzzlingcaptcha 5y ago

I'm glad to see Ken's blog on HN. He does incredible stuff with reverse-engineering old proprietary chips, e.g. the HP nanoprocessor which he reverse-engineered from masks then wrote a disassembler for. https://en.wikipedia.org/wiki/Hewlett-Packard_Nanoprocessor https://en.wikipedia.org/wiki/Hewlett-Packard_Nanoprocessor http://www.righto.com/2020/09/hp-nanoprocessor-part-ii-reverse.html http://www.righto.com/2020/09/hp-nanoprocessor-part-ii-rever...