0-50v variable power supply circuit, at 3A using LM723

This regulator is 0-50v variable power supply circuit. It can adjust output voltage wide range between 0V to 50 volts, and current at least 3A.  The important is the overload protection. It will immediately cut off when a load short circuit.

The output is a voltage regulation circuit. Because they use IC-LM723 ICs to provide better performance. So it is suitable as a power supply circuits for various experiments.

We have presented a lot of variable power supply circuit like these.  For example:

But they ware old circuits for over 20 years ago.

Now we have this project that covers almost all applications.

0-50V 3A Variable power supply

Because it can adjust the output voltage between 0V to 50V. Because we use 2SC5200 transistor to replace the 2N3055 old transistor.  2N3055, though very ancient but it still has many uses we like it.

And also apply current to 3A which better than DC Adjustable Supply 0-50 volts 2A. Hope you will like it.

Technical information

  • Uses the transformer, size voltage: 24V – 18V – CT – 18V – 24V , at current : 3A  to 4A
  • There is an overcurrent protection to prevent damage to the circuit
  • Adjustable Voltage between 0V to 50 VDC (Depending upon  the AC supply voltage of Input)
  • Can apply maximum current to 3A

Working of 0-50v variable power supply circuit

Figure 1 is the circuit diagram of this project.

First of all, the AC-voltage from the transformer-T1 flows through diode D1-D4 to the rectifier to DC voltage.

Second, capacitor-C1  filters that pulsed DC voltage to smooth, before sent through R1, R2 into TR5.

The circuit diagram of 0-50V 3A Variable DC power supply
Figure 1 The circuit diagram of 0-50V 3A variable DC power supply

And there are IC1 is used to control a voltage at OUT point by adjusting VR1 can adjust voltage between 0-50 volts.

Keep reading: ‘0-30V Variable Power Supply at 3A’ »

Two resistors R1 and R2 limit the overload current. They work together with two transistors TR1, TR2.

When the current exceeded, TR1 and TR2 will work. Then, there is an output voltage at lead E  of TR2 through LED1 into 2 pins of IC1.  LED1 is an alarm display.

Thus the circuit stops to provide voltage to the output.

We need to use normal load current that under lower than 3A.
After that, press the switch-SW1 to reset the system to restart working circuit again.

How to make the variable DC power supply

This project has quite many components. You should experience a modest electronic. You can use the perforated PCB. As components layouts in Figure 2
The components layout and wiring
Figure 2 The components layout and wiring

If you want to build this circuit. I have designed this with www.easyeda.com
First, Schematic diagram of 0-50V, 3A variable DC power supply
Schematic of 0-50V, 3A variable DC power supply

Second, Actual-size of Single-sided Copper PCB layout in this project.
Actual-size of Single-sided Copper PCB layout
Print it on 300dpi.

Component-layout of 0-50V 3A variable DC power supply
Third, the components layout of the variable power supply circuit

Components lists of LM723 power supply


  1. IC1 = LM723—High precision voltage regulator  = 1 pcs.
  2. TR1 = BF423—PNP transistor = 1 pcs.
  3. TR2,TR3 = BF422—NPN transistor = 2 pcs.
  4. TR4 = BD140—PNP transistors = 1 pcs.
  5. TR5 = 2SC5200—NPN transistors = 1 pcs.
  6. ZD1 = 36V 0.5W Zener diode = 1 pcs.
  7. D1-D4 1N5401—3A 100V Diode = 4 pcs.
  8. LED1,LED2—LED 3 mm as you want = 2 pcs.


  1. R1,R2 = 0.1 ohms 2W = 2 pcs.
  2. R3 = 56 ohms 0.5W = 1 pcs.
  3. R4,R10 = 100K 0.25W = 2 pcs.
  4. R5,R8,R20 = 10K 0.25W = 3 pcs.
  5. R6,R22,R23 = 1K 0.25W = 3 pcs.
  6. R7 = 15K 0.25W = 1 pcs.
  7. R9 = 2.7K 0.25W  = 1 pcs.
  8. R11,R12 = 5.6K 0.5W = 2 pcs.
  9. R13,R17 = 8.2K 0.5W = 2 pcs.
  10. R14,R15,R16 = 10K 0.5W = 3 pcs.
  11. R19 = 330 ohms = 1 pcs.
  12. VR1 = 10K potentiometer  = 1 pcs.

Ceramic capacitors
C6 = 470pF 50V = 1pcs.

Mylar Capacitors
C2,C7 = 0.1uF 100V = 2 pcs.

Electrolytic capacitor

  1. C1 = 2200uF 63V  = 1 pcs.
  2. C3 = 47uF 50V = 1 pcs.
  3. C4,C5 = 10uF 50V  = 2 pcs.
  4. C8 = 100uF 63V = 1 pcs.
    SW1_____Reset switch normally open pushbutton_____= 1 pcs. PCB,wires,heatsink,nut,screw,and other.

Note: You can buy this KIT here: http://amzn.to/2vKDe7o

Keep reading: ‘0-70V,2A variable power supply’ »

Mounting transistor to the heatsink
When load uses too much current, 2SC5200 is also too heat.
Thus, we must mount the large size heatsink to save 2SC5200.  We can install 2SC5200 transistor to the heatsink as Figure 3.  It is a proper way of mounting the transistor in a heatsink. Using hex nut and metal screw to mount them together by use mica insulator to protect the short circuit.

The mounting the transistor on the heatsink
Figure 3 The mounting the transistor on the heatsink

Connecting the transformer
We see in Figure 2. If you want to use output voltage are 0-50VDC, can connect 18,24 terminal. The output 0-30VDC can connect 0,24 terminal and The output 0-20VDC can connect 0,18 terminal.

connecting wrong polarity voltage is low

But I cannot buy the transformer as Figure 2. So, use 2 transformers to connected with 0-18V and 0-24V in series.  18V+24V = 42V AC
If connecting is the wrong polarity, the output voltage will be low. As Figure 6, the output is 5VAC only.

It means that you connect the transformer wrong. Must return a new polarity wire. We will read voltage about 43V.

Eventually, we will have a successful circuit

Simple Testing and Repair

Connect the transformer as shown in Figure 2. Use a coil of a transformer to match our needing. Then measure the voltage at OUT.

Be careful!! Check and Check again!
Check for error before power on the circuit.

Then, use a voltmeter to measure the voltage at the output. hold it!
Next, supply the AC main to the transformer. While we read voltage the output 0-50V, begin to adjust the VR1.

As Video below.


The repairing
If this project is not working. Please check and check it again. Often, caused by wearing the wrong device position and soldering. Make sure that all the various solder points.

Answer the Question
Mr balasaheb desai: You can use 15V 0 15V transformer, you not use CT or 0 terminal. I think you will have the maximum output voltage of about 40V. Yes, you can use 20K pot, But you should add 20K resistor in parallel with this 20K pot.

See in the picture below, the total resistance is 10K the same in the circuit.

Keep reading: ‘0-30V 0-5A regulated variable power supply circuit’ »


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