I have a requirement to generate approximately 300VDC (low currents, no more than a few mA probably) from a 5V USB supply. It's a prototype for a portable system so total footprint, efficiency and weight are important. The prototype will be an Arduino shield hence USB supply.
I've looked at two approaches; 1) Cockcroft Walton voltage multiplier and 2) flyback boost converter.
1)
I looked at boosting 5V up to 24V using a standard DC-DC converter and then driving a voltage multiplier up to 300V. I simulated this in LTSpice and due to diminishing returns of each successive stage, it looks like it would need over 20 stages, which would need a large board area. And this is using ideal components. Increasing the frequency of the AC input appears to increase the output voltage, how else can I improve the efficiency of this topology? Increasing the initial voltage would of course help, which could perhaps be done by chopping the DC into a step up transformer prior to the voltage multiplier. Not sure if this would save board space, or how big/heavy it would need to be, but I'm less concerned with weight than I am with board size and efficiency. I'm happy to share the simulation.
2)
I then looked at camera flash circuits which are essentially flyback converters. In terms of component count this approach looks much better. Using a (small) 1:100 transformer the 5V input should easily reach 300V. But how does the efficiency of this compare with the voltage multiplier?
For me the flyback is more favorable at the moment. Which leads me to ask the question, is the voltage multiplier used much in practice? I guess it might be used for x2, x3, x4 applications, and for higher voltages perhaps where each stage gains vastly more voltage.
Any advice welcome!