Simple Flyback Driver

In this project i will show you how to make a simple and pretty powerful flyback driver. This configuration can output voltages up to 25 kV or more, depending on the supply voltage. Be careful when dealing with high voltage because it can be dangerous and even lethal when using it incorrectly!

In order to build this driver you will need:

• PCB Prototype board
• 2SC2625 NPN power transistor (or something similar)
• 12V power supply
• 0.33 uF 275 Vac capacitor
• TO-220 aluminium heatsink
• 180 ohm 3W resistor
• 24 ohm 3W resistor
• some wires
• a flyback transformer

We will need two windings, one will be the primary winding and the second one will be the feedback for the transistor.

For the primary wrap 8 turns of a thick wire around the ferrite core in the same direction as in the image. For the feedback you will wrap 7 turns in the same direction. Here you can use a thinner wire, because the current in this coil will be low.

This circuit will have a capacitor mounted at the primary's terminals in order to create a resonant circuit which will increase the voltage output. Based on many experiments, I chose a capacitor with the value of 0.33 uF, because this value gave me the longest arcs. You can experiment with different values to see which one will work best for you.

Also, for this circuit to work properly, you will need to connect the windings of the transformer correctly. The flyback transformer has some internal diodes in series with the secondary coil, and we will need to match the polarity of that diodes, in order for the current to flow and create an arc across the secondary's terminals. The polarity depends on the direction of the magnetic flux created by the primary coil. First, connect the windings to the driver circuit like in the schematic. The inner two wires goes to the transistor, and the outer two to the power and between the resistors, respectively. If this doesn't work, then reverse the primary's terminals. If it still doesn't work, reverse the feedback's terminals also. The combination of connections depends on the transformer model and the direction of the windings.