Variable Voltage, Current Power Supply Circuit Using Transistor 2N3055

 A power supply that does not include the features of a variable voltage and current control can by no means be considered truly versatile. A workbench power supply circuit explained in this article is not only specified with a continuously variable voltage control but is also equipped with the feature of overload or continuously variable current control.

A keen look at the circuit design reveals that it’s actually only an ordinary stabilized power supply circuit, however it yet still provides you with the proposed features very efficiently.

The voltage variations are made by using the preset P2, through a feedback configuration employing the components D1, R7, T2 and P2.

The inclusion of D1 makes it sure that the voltage can be lowered right down to 0.6 volts, which happens to be the forward voltage drop of the diode.

If any other specific minimum value is required then the diode can be replaced by zener diode having the required specified value.

Therefore in our circuit, the transformer being a 0 – 40 V, the output becomes variable right from 0.6 to 40 volts maximum, that’s very handy indeed.

For implementing the current control feature, T3 along with P1, R5 and R4 are involved.

The value of R4 is specifically becomes responsible for defining the maximum allowable output current.

P1 is set to choose the maximum range within the value that’s marked or identified by the resistor R4.

Parts List

R1 = 1K, 5 watt wire wound

R2 = 120 Ohms,

R3 = 330 Ohms,

R4 = to be calculated using Ohms law.

R5 = 1K5,

R6 = 5K6,

R7 = 56 Ohms,

R8 = 2K2,
P1,P2 = 2k5 presets

T1 = 2N3055,

T2, T3 = BC547B,

D1 = 1N4007,

D2, D3, D4, D5 = 1N5402,

C1, C2 = 1000uF/50V,

Tr1 = 0 – 40 Volts, 3 Amp

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