20KVolt Flyback Supply

Introduction

This device, which produce abot 20KVolt at high current output (about 1mA), was created to drive TV cascades or high vacuum tubes for producing X-ray. Anyway it may used for lots of HV experiments explained in the Things to Do section. The components used are quite easy to find: the flyback transformer can be taken from an old color TV and the mains transformer can be found in any electric shop.

Click on the components to see the data sheets:

Theory

This device is a simple high-power oscillator that drive a flyback transformer at 24Khz. The power supply is a simple 55+55 V transformer with the two secoundaries in series. Anyway don't remove R1 because it protects Q1 from overloads. It makes it possible to virtually short-circuit the output without the transistor getting too hot. The diode inside Q2 protect this transistor from extra-tension: so, if you aren't able to find the right version of Q2, you must add any fast-switching diode between its emitter and collector. Because the flyback transformer had a lot of terminals you can find the right winding using a simple tester to measure the less resistence, following the strips on the board, or if you are lucky, looking the diagram of the TV you are working on.

Safety Hints

• Mount any power component ( like R1, R2, Q1, Q2) on a heatsink cooled by a 220V fan (using insulating-kits).

• Close the circuit, mounted on a wooden board, into a earthed metal box.

• And obviously don't touch the output terminals...the contact will be painful!