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.
Table of Contents
Why should make 0-30V variable Power Supply
- 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
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.
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
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.
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.
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 this 0-30v variable power supply project.
We assembled all parts completely on PCB.
This project uses AC power so we must be careful about high voltage.
Finally, we have made this project so successful.
The connecting “12” and “0” will be through a selector switch.
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.
We test this project. As the video step by step.
- Apply the AC power then turn on power switch ON.
- Select Switch to 0-12V Before then Rotate the knob VR1 fully the left.
- 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.
- Toggle switch to “12-24V” then measure the voltage again 330mV to 32 volts.
- Setting the output is 12V, then Apply a 12V 50W as the load.
- Measure the current output when load 12V is 3A maximum.
- Temperature measurement of transistor operation.
How to solve circuit not works
If you made this project but it did not work. You do not worry. It is not a problem. It is a process of your electronic learning. You should have fun solving it.
Here are some basic guidelines for you.
First—No load, No power to this circuit. And Check and Check again with slowly. Surely, something is wrong.
Second—If you check all is correct. You try to power to the circuit again. Then, measure the voltage at.
- TP A(Test point)—It should read voltage about 33VDC. If it is not like this. You should check the unregulated voltage again. Which they include a transformer, bridge diodes, and C1.
- TP B—Also voltmeter should read about 33VDC. But it is zero or lower voltage. Show that parallel resistor, R1-R5 are broken.
Third—check the circuit again. even pins of IC1.
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
Do not should make it!
Here is a very Old 0-30V 2A variable power supply circuit and placing components on PCB.
I show you uA723 is so popular IC! But this is circuit date out, above is best choice!
Source: It is an old circuit from a book 40 years ago.
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