Diagram Diagosis

This power supply can be used to  obtain a regulated power output, variable right from zero to 300 volts maximum. All the devices should be mounted on heatsinks.


You must have come across many power supply circuits which are designed for supplying anywhere between 0 to 25 or at the most 40 volts DC, but the circuit presented here will give you a robust power right from 0 to 300volts continuously variable.

The circuit diagram can be understood with the following points:

As can be seen in the figure, a high voltage transistor BF458 is used as the main load handling device.
Its base bias is controlled by another high voltage transistor BF337 whose emitter is clamped to a stable 24 volts.

An FET is used for selecting the base current of the transistor BF337 via a pot of 1M.

This setting adjusts the base current for the BF337 which in turn restricts the main transistor BF458s voltage and current flow to the output.

The input to the circuit may be derived directly from the mains AC after proper rectification and filtration using a bridge network and a 10u/400V capacitor.

The entire circuit is extremely dangerous to touch, due care should be maintained while making and testing this circuit.