High voltage, big capacitor charger: Flyback vs Push-Pull

Hi,
I want to design a high voltage (~450V), big (~10uF) capacitor charger, it must be fast, possibily quite efficient, and around 60W of power.

Natural choice would be Flyback, but I would also like to evaluate Push-Pull, or even Full-Bridge, as making it smaller - albeit not indispensible - would be a good plus.

Problem is that I suspect that Push-Pull/Full-Bridge topologies may not be a good/ideal choice because of the very low impedance that the converter sees when it has to begin to charge the capacitor. These topologies may work very well for loads that maintain the voltage accross the capacitor, but it's not my case, as I have to completely discharge and recharge it continuously.

Should I stick with Flyback topology in my application then?

Or am I only imagining these Push-Pull/Full-Bridge limitations?

A last question (if Full-Bridge is ok): could you please advice a suitable transformer for Full-Bridge application, input voltage is ~12V, output voltage ~450V, power is around 60W.

Thank you very much.

Cheers,
lchplsnw

Problem is that I suspect that Push-Pull/Full-Bridge topologies may not be a good/ideal choice because of the very low impedance that the converter sees when it has to begin to charge the capacitor

Click to expand...

All topologies face the start-up problem, so that is not a valid reason that would discard one against another.

Consider the voltage the output rectifier must withstand. That could be a way to select the topology, in this HV case.

Flyback is the standard solution e.g. for xenon flashlight power supply since half a century. It doesn't need any complicated control circuit except for voltage control. Push-pull is of course possible but needs an additional output inductor and current control to achieve a reasonable I/V characteristic.

For 60W flyback is a no-brainer, easy to control via PIC uP or similar, is a constant power converter, can limit the input current peak for a const power ramp of Vout, all others are more complex ... you don't state your min input volts, but even from 10V is do-able, we have done these for much larger caps at lower power (5W) to 450VDC.

To charge 10uF to 450VDC (1.01 Joule) at a 60W power transfer rate the cap will charge in an average time of 1/60th of a second - so pretty quickly...

To take best advantage of a flyback, you can work out how the duty cycle should vary keep the input power at 60W all the way thru the charge - this will mean a variable freq if you want fully DCM for quiet (low RFI / EMC) operation. Obviously as the Vout rises the reset time on the flyback core shortens so the duty cycle can be increased all the way thru the charge ... till stop volts are reached.