My first flyback driver with a Royer Oscillator

Ever since seeing videos of flyback transformer drivers from the likes of Keystone Science and Ant, aka ‘high1voltage1rules’ on YouTube, I’ve wanted to get myself a flyback (or ‘line out’) transformer and create my very own driver circuit with the aim of producing purple arcs/coronas and maybe a little O3 (Ozone).

My first successful attempt at getting arcs and a purple, high voltage haze (which produced a lot of Ozone) was thanks to a very simple push-pull type circuit known as the Royer Oscillator and it consists of just five components. This post shows my first cobbled-together attempt at making a driver circuit and I am well aware that having a better understanding of the theory of RLC circuits, resonance, etc will probably help me in future with understanding and building better transformer drivers.

While the high voltage, purple arcs are impressive and strangely beautiful in their own right, driver circuits like this can be useful for numerous HV experiments including Jacob’s Ladders, plasma globes, arc speakers, ionisers, ozone generators and Tesla Coils.

DISCLAIMER - High Voltage is dangerous!

Despite running off just a 12v DC supply, the output of the flyback transformer is 20kV+, so don’t touch the arc and always short out the HV connections once the circuit is turned off, as modern flybacks contain a capacitor and can hold a potentially dangerous charge even when unpowered!

Keep the circuit away from other electronics (a lot of EM interference can be produced) and any other hazards such as water, combustible materials, etc, it’s also a good idea to ensure the room is ventilated, as flyback transformers can produce a lot of Ozone.

The schematic

This is the Royer oscillator in all its glory! In my example I am using 470Ω 2W resistors, the transistors should be identical to ensure reliability and should be mounted on heatsinks as they will get hot. The transistors (Q1 and Q2) should be good power transistors, so small TO-92 transistors like the 2N2222 are not recommended, unless you like the smell of smoke and melted plastic. I’ve seen some circuits with a capacitor across the primary windings (C1), this may or may not be required, same goes for the choke/inductor.

Royer Oscillator schematic

As you can see, the flyback requires a center-tapped winding which connects to the supply voltage (in my case 12v) through the choke. The base of Q1 connects via a resistor to the collector of Q2, while the base of Q2 connects to the collector of Q1 through the second resistor. The collectors of the two transistors provide connections to the two ends of the flyback’s primary winding.

I would quite like to fiddle around with different value resistors and transistors, I’m sure the characteristics such as the gain and saturation voltage of the transistors provide differing results with higher or lower oscillation frequency or bigger/smaller arcs.

As for the flyback, I wound a center-tapped primary winding around the exposed core of my flyback transformer with five or six turns each side of the center tap. My particular model of transformer had just enough space between the core and the body to wind the insulated wire, other makes or models may have more or less space to do your own windings, so your mileage may vary.

This video was my very first attempt at powering on the circuit and getting my very first arcs and corona, not spectacular in terms of the arcing, but that first smell of ozone and seeing the purple corona for the first time really got me excited to learn more about making high voltage drivers/inverters for flybacks, as well as ignition coils and CCFL inverter transformers!

Further Reading