I need to charge a 1000uF 400V capacitor bank off of a 7V LiPo battery within roughly 5 seconds, and have the circuit be as small and light weight as possible. With a constant voltage supply and a resistor to limit the current, the peak current when the capacitors are discharged is around 200mA, and with a constant current power supply the peak current is around 100mA. The constant current supply would also make other parts of my circuit easier, so I would like to have the power supply current limited if possible.

The flyback converter seems like the best topology so far, but how does the flyback compare to other topologies like cascaded boost and boost with autotransformer converters for this kind of voltage?

Would constant current flyback controllers like the UCC28700 and LT3798 work for this? All the ones I can find seem to be designed for stepping down voltages from rectified AC power to a low voltage DC, and I'm not sure if it is possible to run the the opposite way.

There are a few other questions on here about high voltage supplies, but they're all limited to current levels in the uA, so I'd appreciate some direction.

  • \$\begingroup\$ Are those current numbers at 400V or 7V? Because 400V*0.2A = 80W charge supply! That's a big flashgun. \$\endgroup\$ – pjc50 Nov 5 '15 at 12:42
  • \$\begingroup\$ Your requirements are unclear. This site is not geared up to write lengthy generalized comparisons between several techniques of the kind you mention so maybe you can make this easier by being clearer in your requirements. \$\endgroup\$ – Andy aka Nov 5 '15 at 12:44
  • \$\begingroup\$ Yep, in order to charge 1000uF within 5s, it would have to supply 80W peak if it didn't support current limiting, or 40W peak if it did. I'm not sure what's unclear in my requirements, I want to make the lightest possible constant current/constant voltage power supply to those specs. \$\endgroup\$ – ahalekelly Nov 5 '15 at 12:59
  • \$\begingroup\$ After doing some more reading it doesn't seem like push-pull or forward converters are suitable at these voltage levels, so I removed them from the post. Feel free to correct me if that's not the case. \$\endgroup\$ – ahalekelly Nov 5 '15 at 13:02
  • \$\begingroup\$ What part of my requirements were you unclear on? \$\endgroup\$ – ahalekelly Nov 5 '15 at 13:05

There are ICs specifically designed for this, typically marketed as capacitor charger controllers. For instance, the LT3750. They're commonly used for photographic flashes.

One thing to bear in mind is the leakage specification of your capacitor banks; make sure it's very very low, or you'll spend a lot of energy just topping them up continuously. Photographic flash caps are specifically designed with low leakage for just this reason.

  • \$\begingroup\$ I didn't think of looking specifically for capacitor charge controllers, that chip looks like it would work well. I guess flyback is the way to go, I'll see what other photo flash controllers are available. \$\endgroup\$ – ahalekelly Nov 5 '15 at 16:23

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