0-30V Variable Power Supply at 3A

This is cheap adjustable 0-30V 3A Laboratory DC Power Supply circuit. It is high-efficiency regulator circuit using IC regulator UA723 and TIP3055 as power transistor so easy to install. It is designed to protect overload current load maximum 3A

It is best for who find circuits: 0-12V and 0-24V Variable power supply circuit diagram because of its high current and use normal parts new circuit use TIP3055 easy to install.

Technical data
-Need to use transformer: 12-0-12V 4A.
-Voltage output adjustable: 0-30VDC
-Current maximum: 3A

How does it work

Figure 1 the 0-30v variable power supply circuit diagram

As Figure 1 circuit diagram. AC from transformer goes through bridge rectifier diode set which compresses 4 bridge diode changing AC to DC by having C1 as a filter before sending to regulator circuit. Parallel R-value (R1-R5) will be decreased to 2 ohms to detect voltage. If there is over 3A. The voltage at the base is 0.6 volts, making TR3 works. They will high voltage at the collector of TR3 and connect with the base of TR1 making TR1 unworkable, voltage output in down respectively.

Parts you will needs
we need to get all parts as Figure 2

TR1_____BD140___80V 1.5A PNP Transistor
TR2_____TIP3055___60V 15Amp 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
R1-R5_________1 ohms___0.5W 5% Resistors
R6___________50 ohms___0.5W 5% Resistors
R7,R9,R12,R13___100K______0.5W 5% Resistors
R8_____________2.7K______0.5W 5% Resistors
R10____________10K______0.5W 5% Resistors
R11_____________5K______0.5W 5% Resistors
T1______12V-CT-12V, 4A transformer
Heatsink, PCB, Wires, and more…
02_all parts

Let’s build its
Assemble the components on PCB. As Figure 3
03_Assemble the components on PCB

Starting The lowest parts before, to be beautiful. Easy assembly To start with, followed by a diode, resistor and, respectively height and so on. As Figure 4 soldering lowest electronic components.

soldering lowest electronic components

For devices with terminals such as Diodes, Electrolytic Capacitors, and transistors etc.

the components layout and wiring of this project
As Figure 5 is the components layout and wiring of this 0-30v variable power supply project.

We assembled all parts completely on PCB
Figure 6 We assembled all parts completely on PCB.

This project use AC power so must be careful about high voltage
Figure 7: This project uses AC power so we must be careful about high voltage.

we have made this project so successful
Figure 8: Finally, we have made this project so successful.

The connecting “12” and “0” will be through a selector switch as Figure 9.

09_selector switch

For 2 selector;
(1) use voltage 0-12V at “0”
(2) 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.

We test this project. As video step by step

(1) Apply the AC power then turn on power switch ON.
(2) Select Switch to 0-12V Before then Rotate the knob VR1 fully the left.
(3) Measure voltage at the output point, then rotate the VR1 slowly to right, the output voltage starts is 0.3V or 300mV to 16VDC maximum.
(4) Toggle switch to “12-24V” then measure the voltage again 330mV to 32 volts.
(5) Setting the output is 12V, then Apply a 12V 50W as the load.
(6) Measure the current output when load 12V is 3A maximum.
(7) Temperature measurement of transistor operation.

CS9012 If you Cannot find CS9012 transistor you may use equivalent transistor is BC327 PNP transistor. But Different pinout positions between the Emitter and collector.

CS9012 datasheet : http://www.mouser.com/ds/2/149/SS9012-117759.pdf
Ice = 500mA max, Vce = 40max

BC327 Datasheet : http://www.mouser.com/ds/2/149/BC327-30422.pdf
Ice = 800mA, Vce = 40Vmax

Replace a CS9012 with the BC327 equivalent transistors

Read more : 0-30v variable power supply circuits


  1. Muhammad Atif April 13, 2016 Reply
  2. Ron April 23, 2016 Reply
  3. MR OHM 1970 April 24, 2016 Reply
  4. Gokhu May 12, 2016 Reply
  5. Nguyễn Văn Tiến May 14, 2016 Reply
  6. vlady July 28, 2016 Reply
  7. vlady July 29, 2016 Reply
  8. Admin July 30, 2016 Reply
  9. Jesrel August 12, 2016 Reply
  10. daniel December 16, 2016 Reply
  11. Ibrahim January 23, 2017 Reply
  12. Ritcheboy January 3, 2018 Reply
  13. Sanjay January 24, 2018 Reply

Add a Comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.