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0-30V variable Power Supply at 3A

Posted on 23 February, 2018 by Johnathan L. Cunningham
87 out of 100 based on 768 user ratings


If you want to make a 0-30V variable Power Supply. I recommended this circuit. Because you can adjust an output voltage of 0V to 30V, at 3A current, and overload protection.
Also, It is a high-efficiency regulator using IC regulator, UA723, and power transistor, TIP3055. So, it is small laboratory DC Power Supply in inexpensive cost.

Best for who is finding circuits: 0-12V and 0-24V variable power supply circuit diagram. Because It is high current, normal parts, a new circuit design.

  • Modern design—I used to show you the old circuit below, also using LM723. But it powers a current just 2A. And It uses 2N3055 power transistor. So, It is difficult to make. But this use TIP3055 instead. It is slim so easy to install on a heatsink.
  • Output voltage—voltage output adjustable: 0-30VDC
  • Current maximum—all range of output voltage it can power current up to 3A
  • Inexpensive—if you compare with old circuits. this is cheaper than them.
  • Need part—you should use a transformer: 12-0-12V 4A for full current up to 3A.

How does it work

The 0-30v variable power supply circuit diagram
The 0-30v 3A variable power supply circuit diagram

 

Oops! Here is too difficult. Look at  0-30v variable power supply.

As Figure 1 circuit diagram. The order of operation is interesting.

  • Reduce AC voltage—the AC main to a transformer to reduces the AC high to AC low voltage. See below, how to set the voltage as you want.
  • Rectifier AC to DC—Low AC voltage flows through the bridge diodes(D1 through D4) set. They rectify  AC to DC pulse voltage.
  • Unregulated DCV—C1 is a filter capacitor to the pulsating voltage into a steady direct current (DC). Before, send to…
  • DC regulator circuit—the voltage comes to IC1 and some parts. They keep the output voltage is constant. Even the load will draw current too many, the voltage is still stable.If you want to read more detail of LM327 circuits you can visit. Datasheet!But the current out of pin 11 of IC1  is very weak. They need increasing current.
  • Increase current–two transistors TR1 and TR2 are connected in Darlington mode, so a lot of gains.
  • Detect overload—Sometimes it is too much current that the transistor and other parts tolerate it.You look at parallel resistors(R1 to R5) are reduced to 0.2 ohms to detect overload current.If the current exceeds 3A. The voltage across these resistors more than 0.6V.Also, the voltage at the base-emitter of TR3 is 0.6V, making it works. Between its collector-emitter likes, a switch closed.It also connects with base-emitter of TR1. It makes TR1 reduce working, the current is lower.  Then, TR2–power transistor stops working too.Thus, the output is low current, this circuit is safe.
  • Adjustable voltage—You rotate VR1 to change the output voltage between 0V and 30V.
  • Special voltage selector—Adjusting VR1 at low voltage is difficult. Such as 0-12V, 0-10V, and more. But this is special, you can select range of voltage in 2 step, low and high, with SWITCH in a circuit. Low: 0-12V and High: 0-30V. If you cannot imagine Read below!

Let’s build them

First of all get the components.
Parts you will needs
We need to get parts.

All parts on 0-30V variable power supply Circuit kits

IC1_uA723-HIGH PRECISION VOLTAGE REGULATOR
TR1_BD140-80V 1.5A PNP Transistor
TR2_TIP3055, 60V 15A, high-Speed Switching Silicon transistor
TR3_CS9012, 40V 0.5A PNP Bipolar Transistors
D1-D4_1N5401, 100V 3A Rectifier Diodes
C1_4700uF 50V, Electrolytic capacitors
C2_680pF 50V, Ceramic Capacitors
C3_100uF 50V, Electrolytic capacitors
C4_0.1uF 50V, Ceramic capacitors
0.5W 5% Resistors
R1-R5_1 ohms
R6_50 ohms
R7,R9,R12,R13_100K,
R8_2.7K,
R10_10K,
R11_5K,
VR1_5K, Potentiometer
T1_12V-CT-12V, 4A transformer
Heatsink, PCB, Wires, and more…

Note: Here are KITS that I bought from a local store. If you want to save time, can be ordered through the store.

 

Then, Assemble the components on PCB.

Placing components on PCB of 30V 3A variable power supply

Starts with the lowest parts first, to be beautiful. Easy assembly To start with, followed by a diode, resistor and, respectively height and so on. As the image below soldering lowest electronic components.

Soldering a lowest components on PCB first!

Be careful! Some components have polarity like electrolytic capacitors, diodes, transistors, etc. They require a correct placing. If they are the wrong polarity. They will get destroyed from reverse voltage.

The components layout and wiring of 30V 3A power supply

The components layout and wiring of this 0-30v variable power supply project.

We assembled all parts of 3A power supply PCB

We assembled all parts completely on PCB.

This project has high AC voltage, So we must be careful

This project uses AC power so we must be careful about high voltage.

0-30V 3A Laboratory DC Power Supply is complete.
Finally, we have made this project so successful.

Applications

The connecting “12” and “0” will be through a selector switch.

Selector switch to choose, high or low voltage rage

For 2 selector;

  • Use voltage 0-12V at “0”
  • Use voltage output 0-30V at “12,12” the voltage minimum is 0.3V to maximum is 33 volts.
    This way makes the transistor, not overheat.

The output we should connect a 3A fuse in series before to use.

Testing

We test this project. As the video step by step.

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