2N3055 Variable Power Supply

This is simple 2N3055 Variable power supply circuit. This circuit has some advantages such as it it can deliver an output voltage between 1,5 V and 15 V with a 500 mA maximum current and low production cost. If the current consumption do not exceed 350 mA, the circuit has stabilization of better than 2%. Here is the circuit:


The potentiometer is used to vary the output voltage. When overloading is happened, a buzzer will sound a alarm. This circuit use auto-oscillating buzzer, type 24. P1 slider voltage and the output voltage are compared by T4. The T3-T5 Darlington base current is stopped when the P1 slider voltage is 0,65 V higher than the adjusted voltage. C1 and B1 are used to filter the 18V, 1A transformer voltage. The Bz1 starts the alarm, when the output current is more then 500 mA. [Source: eleccircuit.com]