High Voltage Regulated Power Supply

This project is yet another spin-off from my Cosmic Ray Detector Project. As found I needed an effective adjustable high voltage regulated DC power supply with low-noise.

The circuit is based around a cheap CCFL inverter module, in this case a 10W surplus inverter I found for $2 and the common LM2576 3 Amp Adjustable Switchmode Regulator which can be bought over the counter at a good electronics shop like Jaycar.

The output of the inverter is rectified and filtered and and then feed back into the feedback of pin 4 on the LM2576 through a voltage divider. The output of the LM2576 is then used to supply of the inverter.

The LM2576 maybe over-kill but my aim is to be both accessible and cost effective, and although there are better chips available unless your building a few hundred of these, it would be harder to choose a cheaper and more accessible alternative. The spin-off of cause is you can use this circuit with higher wattage inverters for other applications, and the LM2576 is fairly indestructible with thermal overload and short circuit protection built in.

**note The component values in the circuit below maybe changed to achieve higher voltages by changing the value of the 1M resistor, the basic rule of thumb is for every 1M added the voltage is increase by 600V. So if you require 1.2Kv for a PMT, then the value would be 2M. Where the 2K trimpot offers the ability to adjust the output by 300V. The IN4001 is rated for 1000V so two diodes in series will be quite ok for a 1.2Kv supply. The capacitors in the HV filter section can also be wired in series for higher voltages, however this also decrease capacitance and so increase ripple. However if the inverter has a high frequency then this may not be such a big problem.

Below is a another simple circuit using the basic fixed voltage version (in this case 5V) of the LM2576 with the inclusion of a 370K resistor in the feedback provides a fixed 420V DC supply (ideal for Geiger Counter power supplies).