When building and testing electronic project or equipment it is very useful to have a work shop power supply.

Batteries can be used when testing out the modes equipment or project but this can become rather expensive in long-term. Larger items of projects or equipments are often unstable for battery operation even just for testing purposes because it also requires a mains power supply of some sort because it is one of the essentials.  

The unit described here provides an output voltages which is adjustable over range of a little more than 5 to 30volts. The maximum output of current can be either 500mA or 1 amp depending upon the mains transformer used.

Output current limiting is incorporated in the design which is therefore capable of withstanding output short-circuits without sustaining any damage. With the maximum output voltage there is a drop in the output potential of only about 600mV.

When  the output current is taken from zero to full load. This is not as good as the most sophisticated of laboratory power supplies but is much more than adequate for normal amateur requirement.

Power Supply Schematic Diagram

Current Limit Circuit

There is quite a high risk of output short-circuit occurring with a general purpose work shop power supply such as this one and it is virtually essential to incorporate some form of electronic output over load protection circuit. Ordinary fuses are not really suitable as they would probably not act fast enough to protect the output circuit and it would be costly and time-consuming to keep replacing them anyway.

In this circuit the type of overload protection that is employed is output current limiting. This is where the output current is limited to a value which is approximately equal to the design maximum output current of the supply, even if a short-circuit is applied to the output. The supply is unaffected by the current limit circuit until the limit current is reached.


One advantages of this simple type of regulator over most of the more sophisticated types. Configurations that it cannot become unstable and that the component layout is not critical. However, remember that fairly heavy or large amount of current can flow in certain parts of the circuit and connecting wires must be adequate to handle these currents. If the unit is housed in a metal case this must be connected to the ground. In fact, any expose metal parts must be properly grounded and insulated.

Some Tips Before Handling Electrical Devices

Be very careful when handling high voltage components such as transformer and capacitors.  Capacitors and Transformer has capability to store electrical charges.

DO NOT work if you are exhausted or in a rush. Twice ascertain every thing before connecting your circuit to the mains and be prepared to disconnect it if certain thing examines wrong.

DO NOT touch any fraction of the circuit as shortly as it is beneath power.

DO NOT work with moist hands. If you are wearing a flexible chain of bonds, necklace or any kind that may be securing and contact an uncovered part of the circuit  be careful. use always correct mains lead with the correct seal and Ground your circuit correctly.