A well-proven power supply that provides 0V to 20V with current limiting in two ranges of 100mA and 1A.

One of the most useful pieces of equipment an electronics experimenter can possess is a good workbench power supply. Indeed even for those who already have one, a second will often prove useful for projects requiring more than one source of supply or for the occasional design that requires long-term testing.

Ideally a workbench supply should have an output voltage that can be adjusted right down to zero as it is occasionally useful to be able to power a circuit gradually from this when fault-finding. There should also be a fast and effective current limiting facility, again adjustable from zero as this also provides valuable protection when testing circuits.

If the supply can be set to deliver a constant output current instead of a voltage it can also be used as a charger for the many types of re-chargeable battery that are available nowadays, both alkaline and small sealed lead-acid types. The latter are normally charged to a constant voltage but until this is reached a current limit is often required to prevent an excessive charge rate.

Preferably the supply should have two meters so that the voltage and current supplied to the load can be seen at a glance, and most users would probably prefer analogue meters to the digital type for this. Power supplies should be able to meet these specifications whilst being able to react rapidly to any changes in the load it is supplying. This means that the circuit must have a fast response and remain stable for a wide range of output loads, voltages and currents, so the circuit is inevitably a compromise between speed and stability.

The design used for this project should be fast enough for most purposes and has good output stability.