High-Voltage Power Supplies

Introduction

This article documents several high-voltage supplies that I built for plasma experiments and Tesla coils. The designs range from a simple self-oscillating flyback driver to a MOSFET oscillator, a ZVS driver and a microwave-oven transformer.

Single-Transistor Flyback Driver

This is one of the simplest high-voltage sources. A transistor drives the primary of a flyback transformer, while an auxiliary winding provides positive feedback and automatically tunes the oscillation close to the transformer resonance. Suitable flyback transformers can be recovered from older televisions and monitors.

Many monitor transformers contain an internal high-voltage rectifier, which makes the output DC and considerably increases shock risk. Depending on the transformer, a 12 V supply drawing roughly 3–6 A can produce approximately 10–15 kV at several milliamperes. Even high-frequency output can cause severe RF burns, involuntary reactions and secondary injury; it must never be regarded as safe.

MOSFET Flyback Driver

The MOSFET version is more complex but more efficient and adjustable. Instead of a self-feedback winding, an NE555 in astable mode generates the switching frequency. The frequency can be varied continuously, changing the discharge length and input current.

With suitable winding, switching frequency and transistor protection, a flyback transformer may produce tens of kilovolts. In my test, the circuit drew approximately 14 V at 6 A and produced discharges around 5 cm long, corresponding very roughly to 20 kV in air. Higher output requires experimentation with primary turns, core saturation, duty cycle and switching losses.

ZVS Driver and Adjustable Supply

On 6 May 2015 I began another high-voltage source using a zero-voltage-switching (ZVS) driver and an adjustable 1–24 V / 15 A supply. The resonant ZVS topology switches the MOSFETs close to zero voltage, improving efficiency and allowing much higher flyback power. The photographs document the driver, supply and operation at approximately 30 kV.

Microwave-Oven Transformer (MOT)

A microwave-oven transformer supplies the magnetron and typically produces around 2.4 kV at currents approaching 0.5 A. Its power can be close to 1 kW or more. It can power a large Tesla coil or a Jacob's ladder, in which a hot arc rises between diverging electrodes.

Unlike a small flyback experiment, a MOT can deliver unquestionably lethal current directly from the mains. It must never be tested without professional procedures, interlocks, enclosure, fusing, discharge provisions and remote control.

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