4 ms·

There was a HN article about "Dart" (and their Kickstarter) about a month ago. They're building vastly-smaller switching power converters in the VHF frequencie

by beambot 13y ago

There was a HN article about "Dart" (and their Kickstarter) about a month ago. They're building vastly-smaller switching power converters in the VHF frequencies (upwards of 300MHz). I'm not sure about the validity of their claims, though I believe the tech originated at MIT. This could be one compelling route? [1] https://news.ycombinator.com/item?id=7593909 https://news.ycombinator.com/item?id=7593909

xxgreg 13y ago
Very cool. However inverters are DC->AC. I think the correct term for AC->DC converter like Dart is a "rectifier".
- pbsurf 13y ago
  The Dart and nearly all other wall-plug AC to DC converters use a rectify-invert-rectify method. They first rectify the 50/60Hz mains AC to DC, then convert it back to AC at much higher frequencies in the kHz - MHz range, or in the case of the Dart, hundreds of MHz, and finally rectify it again to produce the final DC output. For a given amount of power output, at higher frequency less energy has to be stored in the circuit per cycle (i.e. stored in reactive elements like capacitors), which enables more compact components to be used.
  - hackcasual 13y ago
    It's not AC because the flow of current doesn't reverse direction. It's pulsed on/off. The last stage isn't rectification, it's an LC circuit to smooth out the resulting voltage. The reason higher frequency switching is for smaller value capacitors and inductors.
    - davepage 13y ago
      If we're talking off-line power supplies, it most definitely _is_ AC for the simple reason non-ideal transformers will pass no DC. And, further, inductors and capacitors (LC) are all merely losses to DC signals. These components only have a meaningful function for AC waveforms (even though, in the case of a buck converter, a DC signal is superimposed).
  - pd0wm 13y ago
    However, there is also a downside to a higher switching frequency. In the inverter transistors are used to generate the high frequency AC voltage. A transistor generates no loss if it is in the full on or full off state (saturated). But every time a transistor switches from the on to off state (or back) it goes through its linear region. While in the linear region the transistor acts as a resistor and generates heat. If you increase the switching frequency the transistor switches more often and thus generates more heat. The solution to this problem is to use more efficient transistors or decrease the switching time (the time it takes to switch from high to low, or back). Of course higher switching frequencies also have lots of other problems such as radiation, skin effect, etc.
    - dskhatri 13y ago
      Another solution is to use soft-switching (zero-current or zero-voltage switching) methods.
    - jjoonathan 13y ago
      How does switching current behave in the limit of power transistors? I know that it's significant in high-performance ASICs but I could certainly imagine the junction capacitance of a power-MOSFET being small enough that kHz or even low MHz switching would cost a miniscule fraction of the power being switched. I mean, I've been able to switch the floating gates of sizable MOSFETs by waving my hand at them, I'd be surprised if the power usage at tens to hundreds of kHz was more than a few mW.
      - zAy0LfpBZLC8mAC 13y ago
        There are at least three different ways switching a transistor consumes energy, the power for charging the gate is only one of them and tends to not be the limiting factor in small power bricks. The other two are current spikes in the channel during the switch in logic circuits (because you normally cannot let the output float, which means that during the switch you have to switch on both transistors at the same time, but that's not a problem when driving some inductor/transformer), and energy loss due to voltage drop while the transistor is moving between on and off states (that's where all the heat tends to come from - apart from the heat from the rectifying/free-wheeling diodes).
ChuckMcM 13y ago
I believe you have it backwards, Dart is a switched mode power supply (SMPS) which is sometimes called a converter, and things which take DC and return 90-240VAC are called inverters. (not to be confused with logic inverters) A typical inverter uses MOSFET or IGBT transistors to switch a DC voltage which is then fed through a capacitor as a form of isolation. Typical inverters are use on Solar panel systems to convert PV cells energy into AC, battery backup to AC (Uniinterruptible power supplies), or single phase to multiphase AC to drive AC motors efficiently. One of the reasons they are "big" is because typically they operate at 60 or 50 hz, and at those frequencies if you are using magnetic fields for isolation (like you would if you drove one side of a transformer) the transformers are annoyingly large and hard to make efficient. [1] Many modern inverter start with 280 - 480v DC and use a series of transistors to create an approximation of a sine wave (this is how the cheesy plug into your car lighter inverters usually work). Once you get above a 100W it starts to get a bit more difficult to do cheaply and with reasonable efficiency. Efficiency drains are also present in the upscaling the voltage (whether your using a boost switching circuit or a simple diode/capacitor pump). So getting these things to be efficient is hard, and they are of course generally fairly large per watt. I suspect Google is looking for something to invert PV solar arrays, but high density power conversion is always valuable. [1] That said, a lot of people made high voltage supplies out of using a 555 to switch a transistor on and off which fed the 'low' side of a power supply transformer. I had a Xenon Strobe circuit that did that, made a nice little 600V supply.
- beambot 13y ago
  I'm not saying that Dart's technique is directly applicable. What I am saying: Fundamentally rethinking assumptions (like operating frequency) is probably critical to a breakthrough in inverter design. BTW.... Dart and others (like the iPad recharger [1]) typically convert AC->HV DC (rectifier)->Flyback (at 10's of kHz)->low voltage DC. The intermediate conversion to DC followed by "chopping" at a higher frequency on the flyback transformer allows designers to use smaller magnetics than what would be required of "classic" 50-60Hz wallwarts. I'm sure you're already well aware of all of this given your comment. But so am I (despite the comments suggesting I'm misunderstanding converters-vs-inverters). ;-) If the Google call is for energy generation, then there's also the added difficulty of maximum power-point tracking as well... [1] http://www.righto.com/2014/05/a-look-inside-ipad-chargers-pricey.html http://www.righto.com/2014/05/a-look-inside-ipad-chargers-pr...
rasz_pl 13y ago
This is standard in satellites, heavy is expensive so all power circuits switch in xxx MHz range to save weight on coils/transformers.

by beambot 13y ago

xxgreg 13y ago

Very cool. However inverters are DC->AC. I think the correct term for AC->DC converter like Dart is a "rectifier".

pbsurf 13y ago
The Dart and nearly all other wall-plug AC to DC converters use a rectify-invert-rectify method. They first rectify the 50/60Hz mains AC to DC, then convert it back to AC at much higher frequencies in the kHz - MHz range, or in the case of the Dart, hundreds of MHz, and finally rectify it again to produce the final DC output. For a given amount of power output, at higher frequency less energy has to be stored in the circuit per cycle (i.e. stored in reactive elements like capacitors), which enables more compact components to be used.
- hackcasual 13y ago
  It's not AC because the flow of current doesn't reverse direction. It's pulsed on/off. The last stage isn't rectification, it's an LC circuit to smooth out the resulting voltage. The reason higher frequency switching is for smaller value capacitors and inductors.
  - davepage 13y ago
    If we're talking off-line power supplies, it most definitely _is_ AC for the simple reason non-ideal transformers will pass no DC. And, further, inductors and capacitors (LC) are all merely losses to DC signals. These components only have a meaningful function for AC waveforms (even though, in the case of a buck converter, a DC signal is superimposed).
- pd0wm 13y ago
  However, there is also a downside to a higher switching frequency. In the inverter transistors are used to generate the high frequency AC voltage. A transistor generates no loss if it is in the full on or full off state (saturated). But every time a transistor switches from the on to off state (or back) it goes through its linear region. While in the linear region the transistor acts as a resistor and generates heat. If you increase the switching frequency the transistor switches more often and thus generates more heat. The solution to this problem is to use more efficient transistors or decrease the switching time (the time it takes to switch from high to low, or back). Of course higher switching frequencies also have lots of other problems such as radiation, skin effect, etc.
  - dskhatri 13y ago
    Another solution is to use soft-switching (zero-current or zero-voltage switching) methods.
  - jjoonathan 13y ago
    How does switching current behave in the limit of power transistors? I know that it's significant in high-performance ASICs but I could certainly imagine the junction capacitance of a power-MOSFET being small enough that kHz or even low MHz switching would cost a miniscule fraction of the power being switched. I mean, I've been able to switch the floating gates of sizable MOSFETs by waving my hand at them, I'd be surprised if the power usage at tens to hundreds of kHz was more than a few mW.
    - zAy0LfpBZLC8mAC 13y ago
      There are at least three different ways switching a transistor consumes energy, the power for charging the gate is only one of them and tends to not be the limiting factor in small power bricks. The other two are current spikes in the channel during the switch in logic circuits (because you normally cannot let the output float, which means that during the switch you have to switch on both transistors at the same time, but that's not a problem when driving some inductor/transformer), and energy loss due to voltage drop while the transistor is moving between on and off states (that's where all the heat tends to come from - apart from the heat from the rectifying/free-wheeling diodes).

ChuckMcM 13y ago

I believe you have it backwards, Dart is a switched mode power supply (SMPS) which is sometimes called a converter, and things which take DC and return 90-240VAC are called inverters. (not to be confused with logic inverters) A typical inverter uses MOSFET or IGBT transistors to switch a DC voltage which is then fed through a capacitor as a form of isolation. Typical inverters are use on Solar panel systems to convert PV cells energy into AC, battery backup to AC (Uniinterruptible power supplies), or single phase to multiphase AC to drive AC motors efficiently. One of the reasons they are "big" is because typically they operate at 60 or 50 hz, and at those frequencies if you are using magnetic fields for isolation (like you would if you drove one side of a transformer) the transformers are annoyingly large and hard to make efficient. [1] Many modern inverter start with 280 - 480v DC and use a series of transistors to create an approximation of a sine wave (this is how the cheesy plug into your car lighter inverters usually work). Once you get above a 100W it starts to get a bit more difficult to do cheaply and with reasonable efficiency. Efficiency drains are also present in the upscaling the voltage (whether your using a boost switching circuit or a simple diode/capacitor pump). So getting these things to be efficient is hard, and they are of course generally fairly large per watt. I suspect Google is looking for something to invert PV solar arrays, but high density power conversion is always valuable. [1] That said, a lot of people made high voltage supplies out of using a 555 to switch a transistor on and off which fed the 'low' side of a power supply transformer. I had a Xenon Strobe circuit that did that, made a nice little 600V supply.

beambot 13y ago
I'm not saying that Dart's technique is directly applicable. What I am saying: Fundamentally rethinking assumptions (like operating frequency) is probably critical to a breakthrough in inverter design. BTW.... Dart and others (like the iPad recharger [1]) typically convert AC->HV DC (rectifier)->Flyback (at 10's of kHz)->low voltage DC. The intermediate conversion to DC followed by "chopping" at a higher frequency on the flyback transformer allows designers to use smaller magnetics than what would be required of "classic" 50-60Hz wallwarts. I'm sure you're already well aware of all of this given your comment. But so am I (despite the comments suggesting I'm misunderstanding converters-vs-inverters). ;-) If the Google call is for energy generation, then there's also the added difficulty of maximum power-point tracking as well... [1] http://www.righto.com/2014/05/a-look-inside-ipad-chargers-pricey.html http://www.righto.com/2014/05/a-look-inside-ipad-chargers-pr...

rasz_pl 13y ago

This is standard in satellites, heavy is expensive so all power circuits switch in xxx MHz range to save weight on coils/transformers.