0-30V 0-5A regulated variable power supply circuit

This is a 0-30V 5A variable benchtop power supply circuit, with a voltage and current adjustable system. The output voltage 0-30V and a maximum current of 5A.

Use LM723 as a voltage regulator designed primarily for series regulator applications. By itself, it will supply output currents up to 150 mA. So need to use two transistors 2N3055 for boost up current to 5A.

There are two circuits to learn.

  1. DC Power supply 0-30v 5A, Adjustable regulator
  2. 0-30V 0-5A variable supply with current adjustable

DC Power supply 0-30v 5A, Adjustable regulator

This is DC Power supply 0 30v 5A, an Adjustable regulator is special that the output to 5A current. It uses LM723 DC voltage regulator IC + 2N3055 power transistor x2 to increase current up. So do the current too much than this circuit (easy circuit)

To use transformer 5A, Transistor 2N3055 to Hold Heatsink, VR1-5K to ADJ Volt Output.

5A 0-30V variable regulator LM723 and 2N3055
Circuit Diagram of Variable Regulator 0-30V 5A using LM723 and 2N3055 x 2

We do not offend you, In this Power supply circuit 0-30V 5A is adapted to the work
direct follow want of all of you.

This circuit is still the principle original everything. Just only changes the current limiting circuit. by use the resistors 0.1ohm 5W two pieces for the parallel, to be able to withstand loads as wanted.

We should not forget, use the resistor size 0.1Ω 5W amounting 2 pieces to parallel each other
Then, connected to the emitter of the two 2N3055. To offset features that might be slightly different, these two transistors.

Parts you will need

IC1: LM723
Q1, Q2: 2N4037 or BD140 PNP transistor
Q3, Q4: 2N3055
BD1: Bridge 10A 400V
0.5W resistors
R1, R2, R6: 100K
R3, R7, R8: 10K
R9, R10, R11, R12, R13, R14: 0.1Ω 5W
VR1: 5K or 10K potentiometer
C1: 4,700uF 50V to 7,200uF 50V Electrolytic
C2: 470pF 50V Ceramic
C3: 100uF 50V Electrolytic
T1: Transformer 24V 5A
PCB, big heatsink, and more.

To create just operators device in a PCB form and then to make correct completed is available. Without you have adjusting customized at any the circuit.

PCB layout variable regulator 0-30V 5A
PCB layout

Components layout of 0-30V 5A regulator using LM723 2N3055
The Components layout of Regulator 0-30V 5A using LM723 2N3055

Note: This is so the old circuit.
It does not has a reference voltage for 723 and not fully overload protection. Please look at :

0-30V 0-5A variable supply with current adjustable

This circuit is better than the above circuit. Because use CA3140 for Control Current and Voltage output in easily. And full overload protection.

  • P1-50K for control current
  • R20-50K for Adjustable output voltage
  • R19-5K for fine Adjustable voltage output
  • Transformer—use 5-8A at 32V and 18V voltage. Read more below!

Note: This circuit is not suitable for the beginner. It is best for professional only.

How it works

In the 0-30V 5A regulator circuit below. It uses a precision voltage regulator system.
LM723 is the main part to control the output voltage precisely by itself.

0-30V 5A power supply circuit digagram

This circuit has 2 unregulated power supply, 43V, and 24V.
43V rectifier
It gets the AC voltage of 32V from transformer secondary. To rectify with a bridge rectifier, four 5A diodes.

They power a positive voltage to a collector of two power transistors, 2N3055.  Both transistors are connected in parallel to increase the high current to the output load.

But in the beginning, 2N3055 does not conduct. Because they need to biased current from Q3-BC337  first.

So, we need to have another rectifier.

24V rectifier

This is a power supply for a control voltage regulator system. To begin with, we rectify the 18VAC from the transformer into 24V DC using a D3-diode and C5-filter capacitor.

Then, the 24VDC comes to resistor-1K to power to pin 12(V+) and pin 7 (V-) of LM723.

While the 24VAC also powers CA3140 op-amp IC at pin 7(V+) and pin4 (V-). This is a limiting current system of this circuit.

When the 24VDC flows through 1K resistor pin 11 (VCC) of IC1. It makes the transistor inside can supply voltage output of pin 9.

So, there is a voltage to bias the base of the Q3 transistor. It is working to conduct current from 24VDC through resistor 200Ω 1W to C-E of that transistor.

It results in both transistor 2N3055 get a biased current. So, they can power the current to the output.

Block diagram inside LM723

Block diagram inside LM723

Look at in the block diagram inside uA723. This voltage can be controlled by comparing the voltage pin 4 and pin 5.

Which both inputs of op-amp have 2 pins. Pin 5 is non-inverting and Pin 4 is inverting.

For pin 6 act as set the reference voltage.

If you want to change the output voltage. You change the voltage at pin 4 and pin 5.

In this circuit, we should choose to adjust the voltage at pin 5. Because it controls the voltage in a linear positive.

If the pin 5 voltage rises up. It makes the output pin 9 is positive up.  Of course, there is a lot of biased currents.

Which we can rotate the potentiometer 50K to adjust the output voltage 0-30V in normal and 5K in fine adjusting.

Limited current
CA3140 is Bi MOSFET Operational Amplifier, it acts as limit the current in this circuit. If the current is more than 5A. This will cut off the regulator immediately—with stopping 2N3055 transistor working.

How it works?—We use a comparing voltage between pin 2 and pin 3. When the transistor Q1 works over current than normal. Then, pin 3 will compare the voltage with pin 2.

It makes the positive voltage out of pin 6 to bias the base of BC549.  Then, BC549 pull the voltage at pin 13 of LM723 down and no output voltage. This circuit safe.

Parts you will needs
IC1: UA723
IC2: CA3140
Q1,Q2: 2N3055- 15V 60V transistor
Q3: BC337-0.8A 40V NPN transistor
Q4: BC549-0.4A 40V NPN transistor

0.5W  5%  resistors Except special
R1, R3: 1.2Ω  5W
R4: 100Ω  5W
R6: 2.2K   5W
R5,R7: 100K
R9,R10: 1K
R8: 100Ω 1W
R9, R10.: 1K
R11: 150Ω 0.5W
R12: 5.6K
R18: 3.9K
R16: 47K
R13: 1.5K

Electrolytic Capacitors
C1: 2,200μF 50V
C3,C4,C5: 220μF 50V
C7: 47μF 50V

How it builds

First of all, we should get all the components on the lists below. Then, get the PCB. You can also use a perforated board. Look at the PCB layout and the components layout.

PCB layout of 0-30V 5A power supply using LM723 and CA3140
The PCB copper layout

Components layout of variable regulator_0-30V 5A LM723 CA3140_2n3055
The component layout

Note: I am sorry that tell you. I never build this circuit. So, I cannot confirm it works. If you are looking for 0-30 variable power supply.

I recommend

They are tested.

Also, You can increase current up to 5A with adding a transistor-like this.

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I always try to make Electronics Learning Easy.

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