Cheap adjustable 0-30V 2A Laboratory DC Power Supply

This 0-30V power supply is the variable voltage Regulator at 2A max, by used IC-723 for control volt stable regulated. The 2N3055 power transistor for boost up current to 2 Amp.

It suitable for general electronics work shop. Because it is a simple circuit and easy circuit. In addition to this has the over current protection as well.

This circuit is designed using LM723 voltage regulators IC –DIP 20pin maintain a constant voltage, and a power transistor as the way through the current to can be used up as wanted.

The circuit was designed also with overload protection or short circuit in the output. The amount of current flow will not exceed the set. Because it is monitored constantly by R4.

When the current flows through the R4, until the 0.6V voltage drop across it. Making Q3 runs short the bias voltage between the base-emitter of Q2, it stopped working. Now, the Q1 stop working because does not has the bias voltage to base pin its, The output voltage is zero or down quite a close to zero.

The potentiometer VR1 acts as adjust the voltage that enter to the LM723 for the volt output by you want. By the our circuit can adjust the voltage output from 0V to 30V.
In use real, because the properties of the transistors used and values error of each device. Therefore, if the circuit can not be supply up to 2 A. Try changing the value of R4 is a lower value, until has the maximum current desired. Should be to use transformer 3A. The Transistor to Hold Heat sink as well.


Parts you will need
Q1_____________2N3055____100V, 15A, 115W, >2,5MHz NPN transistor
Q2,Q3__________BD140 or 2N4037______80V 1.5A PNP Transistors
D1,D2__________1N5402_____3A 100V Diodes
R1,R8__________10K______1/2W Resistors tolerance: 1%
R2,R3,R6_______100K______1/2W Resistors tolerance: 1%
R4_____________0.3 ohms 5W____Resistors tolerance: 5%
R5_____________47 ohms______1/2W Resistors tolerance: 1%
R7_____________2.2K______1/2W Resistors tolerance: 1%
R9_____________1.8K________1/2W Resistors tolerance: 1%
C1_____________2,200uF 50V_____Electrolytic Capacitors
C2_____________470pF 50V Ceramic capacitor
C3_____________100uF 50V____Electrolytic Capacitors
T1_____________3A, 24-0-24V transformer

How to builds.
The Figure 2 is the PCB layout and Components layout of this projects

the PCB layout and Components layout

The another circuits is similar.

Power supply regulator 0-35V 2A by IC LM723 + Transistor 2N3055 & BD140 & A671

The Circuit power supply regulator 0-35V 2A by IC LM723 + Transistor 2N3055 & BD140 & A671. It nice Power supply, For all electronic user, To use transformer 3A, Transistor to Hold Heatsink, To adjust the output voltage VR1 – 1K
OUTPUT : 0V to 35V , 2A

The power supply variable regulator circuit 0-35V 2A size using IC – LM723 + Transistor 2N3055 & BD140 & A671

The PCB board of Power supply variable regulator circuit 0-35V 2A by IC LM723 + Transistor 2N3055 & BD140 & A671

To use transformer 3A, The VR1 – 1K perform fine Voltage output get since 0V arrive at 35V. Transistor 2N3055 numbers should stick let off enough heat. LED1 for show over load of output.

Although the circuits are is not the same. But it will help you succeed in certainly electronic projects.


  1. godwinzh May 14, 2016

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