China special boost converters

Sorry, try this:

There's quite a range of these on eBay, apparently the same PCB, but with varying assembly options, prices ranging from $5 + $0.85 shipping to $7.75. Some say the circuit is ZVS. Some mention a dual bipolar output available. To my mind the most interesting part is the transformer.

An eBay flyback boost circuit rated at 200W (600W claimed) may be similar, but uses a toroid inductor.

One has to supply a 12 to 24V input == so starting at 120 or 230Vac, we make 100W low-voltage dc, and then step it up again. It'd be convenient to have an AC-line supply, with an adjustable HV DC output.

It looks like I got the one with the bipolar output as it seems the output terminal block has three lugs; I can't recall if that's what I ordered but looks like that's what they shipped. Is that option what makes the transformer interesting? It should be straightforward enough to draw up a schematic from inspecting the traces on this one; I think it's only double-sided.

I think I have an appropriate set of power resistors to use as a dummy load to run it up to near full load at max output voltage, I'd like to see if it does meet its specs and what the output ripple is like towards the limit.

I got one of those to play around with some Soviet GM tubes. I think I paid a bit less, but whatever.

Current draw is weird- huge current with little load, then settles down.

--sp

It's a voltage doubler on the output with the center grounded, so if your load is grounded you can pick either +380 or -380 max. Probably the feedback is from the +.

BTW, sorry if this is obvious, but you need to move that jumper on the bottom to get below 10V- that bypasses the 78L09 regulator for input voltages between 8V and 16V.

Thanks for identifying the other two chips. The numbers have been scraped off the SO8's on mine.

--sp