5V Regulated Power Supply Circuit using Transistors

A 5V regulated power supply is very important in electronics as it is used to run many digital circuits, for example, microcontrollers, sensors and logic ICs.

This 5V Regulated Power Supply Circuit using Transistors gives stable 5 volts DC output.

It uses transistors for voltage regulation and so it can handle more current than IC regulators.

Firstly, AC voltage is changed into DC voltage and then this DC voltage is filtered properly.

After that the transistors control the output voltage, so the voltage stays constant even when load changes.

This circuit design is simple and is also easy to understand, hence it is very good for beginners.

Components are with low cost, easily available and is ideal for lab use and learning purpose.

Circuit Working:

Parts List:

This circuit converts AC to DC and then it regulates voltage to 5V.

First, AC mains supply enters switch S1 and then fuse F1 protects the circuit.

After that transformer steps down voltage and it converts 230V AC to 6.3V AC.

Next, this AC goes to bridge diodes D1 to D4 and so AC is converted into pulsating DC.

Then capacitor C1 filters this DC and therefore, ripple is reduced.

Now Zener diode provides reference voltage and it gives 6.2 volts fixed.

Then resistor R1 limits Zener current and after that transistor Q2 senses voltage.

It works as error amplifier, if voltage increases it controls Q1 and so output remains stable.

Next, power transistor Q1 supplies load current and it handles high current safely, as also it reduces voltage to 5V.

Finally, capacitor C3 removes noise with output DC becomes clean and thus, regulated 5V is available at output.

How to Build:

To build a 5V Regulated Power Supply Circuit using Transistors following are the steps we need to take care while connecting the circuit:

• Start the circuit by collecting all the required components as shown in circuit diagram.
• Transformer primary pins connect to AC mains.
• Secondary pins connect to bridge rectifier D1-D4.
• Capacitor C1 positive pin goes to rectifier output.
• Negative pin goes to ground.
• Zener diode cathode goes between R1 and base circuit of Q2.
• Anode goes to ground.
• Resistor R1 one side goes to rectified DC.
• Other side goes to Zener cathode.
• Resistor R2 one end connects to output and other end goes to GND.
• Transistor Q2 BD137 base pin goes to junction of Zener diode and anode of capacitor C2.
• And cathode of capacitor C2 goes to GND.
• Emitter pin connects to base of Q1 transistor.
• Collector pin goes to rectifier output.
• Transistor Q1 TIP42 base pin connects to emitter of Q2.
• Collector pin connect to rectifier output.
• Emitter pin goes to regulated 5V output.
• Capacitor C3 positive side goes to output.
• Negative side to ground.
• Connect S1 switch and fuse F1 at the AC input.
• Connect fuse F2 at +5V DC output.

Note:

• Always use heat sink for Q1.
• Check polarity of capacitors.
• Use proper fuse value.
• Do not touch AC side when powered.
• Test with multimeter before load.

Conclusion:

This 5V Regulated Power Supply Circuit using Transistors is very useful.

It is simple and easy to build and is perfect for beginners.

Also it gives stable output and therefore, it is good for learning electronics.

So every student should try this project.

References:

Datasheet TIP42

Datasheet BD137