0-30V 3A Adjustable DC Supply

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

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

How does it works
As Figure 1 circuit diagram. AC from transformer goes through bridge rectifier diode set which compress of 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 connecting with the base of TR1 making TR1 unworkable, voltage output in down respectively.
Figure 1 the circuit diagram

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

02_all parts
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…

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 resistors 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 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 use AC power so 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 over heat.
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 the left.
(3) Measure voltage at the output point, then rotate the VR1 slowly to right, the output voltage start 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 load.
(6) Measure the current output when load 12V is 3A maximum.
(7) Temperature measurement of transistor operation.

If you want this PCB layout please contact me: or buy it below.
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  1. Ibrahim January 23, 2017

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