Single transistor / blocking oscillator supply

[Sch3mat1c]

The primary is 400uH, wound in two sections. I used a double E core, ungapped, which happened to measure 90nH/T^2 and 160At saturation. These things are regularly used in computer PSUs for essentially the same purpose, a single-transistor standby/controller supply.

Efficiency is fairly low, around 67%, which can be improved by increasing drive and adding what looks like a current limiting transistor. I haven't done this yet.

Slightly earlier version, breadboarded:



This had a smaller transformer, with no particular attention to winding, resulting in particularly high leakage inductance, as can be seen in the collector voltage waveform:



Current waveform (measured across 0.47 ohm emitter resistor):



Tim