All workshops or laboratories must have a power supply for general purpose that can supply voltages and currents.
This time we get a adjustable power supply with output voltages between 1.2 and 25V the maximum current of 4A. This is very useful for laboratory power supply or workshop power supply.
As shown in the Variable 4 Ampere /25V Power Supply scheme that the circuit consists of three stages. The first (which is formed by a transformer, bridge rectifier and an electrolytic capacitor 10000μF) is responsible for isolating and reduce the voltage, improve and filter. The second phase (consisting of, BC327 transistor integrated circuits and components attached) is responsible for providing a reference voltage which is used to determine, together with the potentiometer and top resistor, voltage applied to the driver transistor and power. It should be noted that they made a resistive and non-switched control (switching) so the voltage at the emitter is pulsed. Then we have a small output filter formed by the electrolytic capacitor and terminals.
The transformer must provide a voltage of 25V with a current rating of 6A and its primary voltage should be chosen according to the power supply in your area. 2N3055 transistor must be mounted on a good heat sink, while sufficient for BD137 a clip-type heatsink. The 100nF capacitor connected in parallel with the power to the μA741 should be located as close as possible to optimize it for filtering the source.