~2W Mini Isolated DC to DC Converter (Common Push-Pull TL494 + 2N2222 + BD139) @Magneticitist

Uploaded January 2026 | Updated September 2026, 3 weeks ago

Again just for fun. The high potential rating of this tiny transformer is actually 3.75kV pri to sec. It's 100 volt (micro) seconds rated so I think I could do 3W without much worry but then I'd need to actually design a low loss PCB. The idea was to put a 12V regulator on the front for the TL494 and BJT gates, and another ~20V linear to keep the power rail constant at ~24VDC input.. All I had was these BJT's and UF4007 diodes so I figured this may be a good representation of the slack lower end of capability (adding some small PNP's to the drive stage would also help if you felt like it). If I can grab some good 100V mosfets it looks like I can just source a similar pulse transformer and make a few of these but much smaller and more efficient.
My 12V fan load pulls exactly 2W when driving it at 15V. Running it that way for quite a while gave me no impression anything was struggling, so 2W is my low estimate here. Efficiency-wise at close to the bare acceptable minimum it seems promising to me. The downside is if you run too high of a duty cycle with a transformer so small you probably won't be able to put anywhere near 24V into it. I had to deal with lower on times after the TL494 through switching rise times to keep it reasonable.

TL494 VCC - 12VDC (linear regulator)
RT is about 8K and with 1nF CT gave me the 70khz.
2N2222's - 330 ohm base resistors, 2.2K pullups, 12K pulldowns
BD139's - ~47 ohm base resistors, 1.2K pullups, 6.8K pulldowns
No added dead time

~2W Mini Isolated DC to DC Converter (Common Push-Pull TL494 + 2N2222 + BD139)

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