ZVS Driver: The Heart of High-Voltage DIY Projects
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Even during home experiments, there is often a need to use high voltage, much higher than the 230V found in standard lighting circuits. At such times, high-voltage converters of various kinds are particularly useful. These are electronic circuits that step up the voltage. Below, I will present one of these circuits, which, in my opinion, best combines simplicity of construction with good performance. This device was first built by Mr. Vladimiro Mazzilli.
Original schematic:
As we can see, the schematic is very simple and contains few components. I used IRF450 MOSFETs, which work very well. The high-voltage transformer comes from an old TV set. The high-voltage secondary winding (usually embedded in white plastic) should remain unchanged. The primary winding should be wound according to the instructions on the schematic, with a center tap.
Warning: I do not recommend building the ZVS circuit for beginners without experience in handling high voltage. The output of the device carries voltage in the range of several thousand volts (several kV). The electric arc is extremely hot: it can instantly char the skin and flesh of a careless experimenter. The author assumes no responsibility for any injuries, damages, or losses resulting from the construction or use of this device; proceed at your own risk!
This converter has very high efficiency. This is because the transformer’s primary winding, together with the capacitor connected in parallel, forms a parallel resonant circuit. Due to the push-pull connected transistors, the condition for oscillation of the resonant circuit at its resonant frequency is ensured. For a parallel resonant circuit, current resonance occurs. The alternating current flowing through the transformer winding thus reaches its maximum possible value. Zener diodes protect the transistor gates from voltage surges.
The capacitor must be of good quality. The best choice would be a pulse capacitor designed for power supplies. I used a battery of four such capacitors of 0.25µF each, resulting in a total of 1µF. These capacitors must be rated for a voltage at least three times higher than the supply voltage.
The impedance-matching coil is best wound on a toroidal core e.g. from a damaged computer power supply. Approximately 20-30 turns of wire with a diameter of 0.5 - 1.0mm (AWG 20 - AWG 18) is sufficient.
All circuit components should be mounted securely on an appropriate board. A printed circuit board (PCB) can be used, but I used a board made of thick pressboard. It was screwed onto a suitable heatsink that dissipates the heat generated by the transistors:
The transistors are not visible because they are located under the board and are screwed to the heatsink through silicone insulating pads.
The circuit worked so well that after some time, I made a newer version:
After assembly, the circuit should work right from the first power-up. However, make sure that the power source has sufficient current capacity, as the current can reach several amperes. The voltage at the output of the secondary winding can reach several or even tens of kilovolts (kV), with a high current. This should be handled with extreme caution! An electric arc a few centimeters (about an inch) long, with a temperature of several thousand degrees Celsius (several thousand °F), is generated. Do not use copper wires to ignite the electric arc, as they may melt. The transistors may generate significant heat during maximum arc stretch.
The converter also works with other types of high-voltage transformers and flyback transformers from modern TVs and CRT monitors.
Thanks to this device, many interesting experiments can be conducted:
- Electric wind
- Electrostatic motor
- Corona discharge
- Heating by induced electric current
- Kirlian photography
- Plasma globe
Using this converter (similarly to my Tesla coil), you can generate discharges in the gas filling light bulbs. The inert gas inside the bulb has sufficiently low pressure to trigger avalanche ionization. This manifests as visible discharges and glow.
To observe the discharges, it is best to use two secondary windings connected in series and placed on a common core:
One terminal of the secondary winding must be properly grounded, while the other should be connected to the light bulb socket. Light bulbs of any power rating can be used, from 40 to 100 watts (W), or even more. I used a light bulb with a power of… 800W. In the photo, you can compare its size with a 100W bulb.
When the ZVS is turned on, bright blue discharges should be visible inside the bulb:
When a metal object is brought close to the bulb, the discharges converge toward it. This can be seen in the video below.
Have fun and learn a lot! :)
Have fun and learn a lot! :)
Further readings
- Blanchard J., The History of Electrical Resonance, Bell System Technical Journal, 1941, 20(4), pp. 415-433
- Knowlton A.E., Standard Handbook for Electrical Engineers (8th ed.), McGraw-Hill, 1949
- Plamitzer A.M., Maszyny elektryczne, Warszawa, Wydawnictwa Naukowo-Techniczne, 1982, pp. 35
Marek Ples