80v supply -> 12v output

Ahhh, the bad news is I dont think I do. Its been 15 years now. I might be able to sketch it from memory, will try that later.

NT

In article , Jim Drew wrote: [...]

At 100 units, I'd go take a look at Vicor's web site and buy a switcher. Your time has got to be worth something.

Vcc ! T1 ((((((((((((-+-((((((((((( ((((((((( ! T1 ! ! ---- AC to ! Vcc ! ---/\\/\\------ rectifier ! ! ! ! / ! ! \\ R1 ! ! / ! ! \\ ! c \\! ! T1 R2 !/ c Q1 !--+-+-(((((-/\\/\\--+---! Q2 /! ! ! !\\ e e ! --- D1 D2 --- ! ! ^ ^ ! ! ! ! ! ! GND GND ! +--------+------------------ ! ! \\ --- C1 / --- \\ R3 ! / GND ! GND

It runs as: Q1 turns on until the T1 saturates and then it flips over the Q2 on.

R1 may have a capacitor in series with it. Once the circuit is running, D1 and D2 conduct when Q2 and Q1 are biased on so R1 stops mattering. When power is first applied. R1 biases Q1 on enough to get the oscillation started.

The T1 winding that provides the base drive should make a peak voltage of more than 2V but less than about 10V. The Watts R2 eats are just wasted.

R3 is really optional as is C1. R3 normally has just a few tenths of a volt on it. It can kill the oscillations if the load side gets a dead short on it.