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Just the other day I idly wondered how LED "light bulbs" regulate down their 230V (here in central Europe, at least) to the ~2V needed per LED. Although it's f

Just the other day I idly wondered how LED "light bulbs" regulate down their 230V (here in central Europe, at least) to the ~2V needed per LED. Although it's from a different starting point (AC, not DC), after reading the article it seems they could use an AC->DC converter and then a charge pump. Is that what they actually use? Or is there something easier/cleverer when starting from AC?

wrenzh 4y ago
For household LED bulbs almost always Flyback.
toast0 4y ago
They probably have a switching power supply, but if you want really simple and low parts count, you'd do a transfomer down to something nicer, have a full bridge rectifier, a capacitor, a current limiting resistor, and then put all the leds in the bulb in series; that way you don't need a big ratio for the transfomer... although maybe that's not a big deal, and you may prefer to not need a higher voltage capacitor, or a more failure tolerant parallel wired LEDs. You could have a linear regulator in there too, but careful component choices may allow that to be omitted. But switch mode power supplies are probably more efficient and highly miniturized, better adapted to different line voltages, etc. All around a better choice. Some sort of smarts are needed to work well with dimmers as well.
- NotYourLawyer 4y ago
  Transformer is probably a lot more expensive than what they use.
NikkiA 4y ago
LED bulbs usually use the most basic of power supplies, the capacitive dropper[0], the downside is that they tend to die easily. Also, the LED diodes themselves will often be multiple in series (a string), or series-parallel (several strings in parallel) depending on the bulb, that end up needing more than just 2V, anywhere from 12V to 60V or so per string of diodes. Sometimes the high power diodes being used are themselves a series chain of diodes on a singular piece of silicon encased in a blob of phosphor, so that the diode package ends up needing 12V or so. These are often referred to as 'COB' diodes. (apologies for the RAS syndrome, but saying 'LE diodes' or just 'LED' to refer to the individual light elements when talking about 'LED bulbs' is too confusing otherwise) [0] https://en.wikipedia.org/wiki/Capacitive_power_supply https://en.wikipedia.org/wiki/Capacitive_power_supply
- djmips 4y ago
  How about. "Also, the LED elements will often be in series (a string)"
- rcxdude 4y ago
  RAS syndrome is not a bad thing for exactly the reason you've just mentioned! redundancy is common in language, it does actually serve a useful purpose and this particular redundancy confuses no-one.
- userbinator 4y ago
  Capacitive droppers are the most reliable for LED bulbs in my experience, because they are very simple and there's not much to go wrong. It's usually the IC-based ones that die first.
  - comboy 4y ago
    Just to add a data point, I have the opposite experience based on just a few bulbs of different brands I disassembled over the years.
    - userbinator 4y ago
      What has failed in them?
      - NikkiA 4y ago
        In my experience, it's usually the capacitor that pops, but my experience is mostly with GU10 form factor bulbs, which have the downside of being very compact and fitted in fittings that don't have good heat reduction properties resulting in everything running hot, even in a LED bulb that should be cool. Even the cheapest LEDs last longer than standard halogen GU10 bulbs though, so there's that.
      - lightedman 4y ago
        Capacitor usually blows - they don't like operating really hot and heat removal inside those small form factors is a serious challenge. Also, many times, the whole power converter is encased in a semi-insulative rubber, so that just compounds the problem.
rokweom 4y ago
Nowadays most basic LED bulbs just put the LEDs in series to get the combined voltage drop close to the rectified and filtered mains voltage, and a linear regulator takes care of the rest. This is cheaper and simpler than other methods mentioned by other users (switching or capacitive dropper). Here's a nice video with a schematic and even a way to hack them to lower the power: https://youtu.be/5HTa2jVi_rc https://youtu.be/5HTa2jVi_rc (feel free to skip around, no need to watch the whole video to understand it)

wrenzh 4y ago

For household LED bulbs almost always Flyback.

toast0 4y ago

They probably have a switching power supply, but if you want really simple and low parts count, you'd do a transfomer down to something nicer, have a full bridge rectifier, a capacitor, a current limiting resistor, and then put all the leds in the bulb in series; that way you don't need a big ratio for the transfomer... although maybe that's not a big deal, and you may prefer to not need a higher voltage capacitor, or a more failure tolerant parallel wired LEDs. You could have a linear regulator in there too, but careful component choices may allow that to be omitted. But switch mode power supplies are probably more efficient and highly miniturized, better adapted to different line voltages, etc. All around a better choice. Some sort of smarts are needed to work well with dimmers as well.

NotYourLawyer 4y ago
Transformer is probably a lot more expensive than what they use.

NikkiA 4y ago

LED bulbs usually use the most basic of power supplies, the capacitive dropper[0], the downside is that they tend to die easily. Also, the LED diodes themselves will often be multiple in series (a string), or series-parallel (several strings in parallel) depending on the bulb, that end up needing more than just 2V, anywhere from 12V to 60V or so per string of diodes. Sometimes the high power diodes being used are themselves a series chain of diodes on a singular piece of silicon encased in a blob of phosphor, so that the diode package ends up needing 12V or so. These are often referred to as 'COB' diodes. (apologies for the RAS syndrome, but saying 'LE diodes' or just 'LED' to refer to the individual light elements when talking about 'LED bulbs' is too confusing otherwise) [0] https://en.wikipedia.org/wiki/Capacitive_power_supply https://en.wikipedia.org/wiki/Capacitive_power_supply

djmips 4y ago
How about. "Also, the LED elements will often be in series (a string)"
rcxdude 4y ago
RAS syndrome is not a bad thing for exactly the reason you've just mentioned! redundancy is common in language, it does actually serve a useful purpose and this particular redundancy confuses no-one.
userbinator 4y ago
Capacitive droppers are the most reliable for LED bulbs in my experience, because they are very simple and there's not much to go wrong. It's usually the IC-based ones that die first.
- comboy 4y ago
  Just to add a data point, I have the opposite experience based on just a few bulbs of different brands I disassembled over the years.
  - userbinator 4y ago
    What has failed in them?
    - NikkiA 4y ago
      In my experience, it's usually the capacitor that pops, but my experience is mostly with GU10 form factor bulbs, which have the downside of being very compact and fitted in fittings that don't have good heat reduction properties resulting in everything running hot, even in a LED bulb that should be cool. Even the cheapest LEDs last longer than standard halogen GU10 bulbs though, so there's that.
    - lightedman 4y ago
      Capacitor usually blows - they don't like operating really hot and heat removal inside those small form factors is a serious challenge. Also, many times, the whole power converter is encased in a semi-insulative rubber, so that just compounds the problem.

rokweom 4y ago

Nowadays most basic LED bulbs just put the LEDs in series to get the combined voltage drop close to the rectified and filtered mains voltage, and a linear regulator takes care of the rest. This is cheaper and simpler than other methods mentioned by other users (switching or capacitive dropper). Here's a nice video with a schematic and even a way to hack them to lower the power: https://youtu.be/5HTa2jVi_rc https://youtu.be/5HTa2jVi_rc (feel free to skip around, no need to watch the whole video to understand it)