# Driving a flyback with pure AC sine wave

I am quite confused about flyback drivers. I have a high frequency (up to 50 kHz) AC sine wave generator, and I would like to use it to generate some arcs on a flyback. So I thought I could just wind a primary coil around the flyback core and get some arcs between the secondaries. Is that correct? Do I need to rectify my generator output?

P.S.: If my generator couldn't be used for this project, I will build the Mazzilli ZVS flyback driver.

Any help would be appreciated :).

My flyback is the same from the picture below.

• That sort of "flyback" transformer (line output transformer) requires a rectangular wave drive signal, generally with a ~20% duty cycle if memory serves. I doubt you'll be able to get it to work properly with a sine wave input. The ZVS flyback driver is the way to go. Commented Nov 20, 2017 at 17:20
• Oh! Thanks for the answer! Just one more thing: Should the rectangular wave be always above 0V? Or can I use AC rectangular waves? Commented Nov 20, 2017 at 17:27
• That transformer has a HV diode inside, so you will saturate it by using AC. It's a flyback and it needs all circuitry as a flyback, see some TV schematics. Commented Nov 20, 2017 at 17:44

The Mazzilli Zero Voltage Switching (ZVS) driver consists of two parts:

• The switching circuit
• The flyback transformer

The switching circuit consists of a pair of IRFP250/260 MOSFETs and a pair of zener diodes that step up the 12 V d.c. 3A input into high frequency sinusoidal signals that drive the flyback transformer. The switching voltage which turns on and off the MOSFETs drops at a 660 nF capacitor rated at 1200 V and two 200 μH inductors which are parallel to the primary winding coil of the flyback transformer.

The operation is as follows:

Upon application of power, current flows through both sides of the MOSFET’s drains. One of the MOSFETs turns on faster than the other and more current draws to this MOSFET. This causes the other MOSFET to be turn off. The voltage starts to rise and fall sinusoidally. When Q1 turns on, the voltage at drain of Q1 will be ground while voltage at source of Q2 rises to a peak and drops back down during the one half cycle of LC tank. As the voltage of the source of Q2 drops to zero, the gate current to Q1 is also removed and as a result, Q1 turns off. This causes the drain voltage of Q1 to rise and Q2 turns on. The MOSFETs switch when there is least power induced. The same process repeats for the second half cycle. To prevent the oscillator from drawing huge peak currents and exploding, L1 is placed in series with the power supply functioning as a choke to mitigate current spikes. R1 limits the current that charges the gates to avoid damage of over current at the MOSFET. R3 of 10k pulls the voltage down to ground to avoid latchup. The Zener diodes regulates the voltage at 18 V. D1 and D2 ensures the gates voltage down to ground when the voltage on the opposite leg of the tanks is at ground.

The waveforms at R1 and R2:

A DC ½ phase was observed at the pair of resistors. The peak voltage of the half DC pulses dropped slightly to 11.46 V as a result of the zener diode regulation.

Half cycle sinusoidal signals alternatively oscillates at the drain-source (Vds) of the pair of IRFP260 MOSFET as shown in Fig. 4. The transistor is also an amplifier in the ZVS circuit for ensuring maximum power delivering to the next stage. Hence, fast switching transistor used was used. Each of the transistor connects to the inductor coil is mirrored to each other.

The waveforms of VDS of the MOSFETs:

Finally the output of the switching circuit across C1,

There is an improved version called the Andrinerii ZVS driver, which reportedly has a 30-35 % improvement in performance. This adds one pair of coils consisting of three turns (in the same direction as the primary1) in series with 100 Ω resistors. Each coil and resistor is added in parallel to each half of the primary coil, like so:

1 Otherwise the driver will be damaged.

• Thank you! Your answer helped me a lot! Exactly the info I was look for :) Commented May 23, 2019 at 22:34