A Dual polarity power supply unit is capable of providing both +/- supply voltage with respect to the users’ needs. Dual polarity power supplies are created mostly to power up operational amplifier circuits and other circuits that require dual supply voltage. They are also used in designing electronic test benches and trainer boards. They are easy to design and maintain, relatively cheap and reliable So, in today’s tutorial, we are going to design a ±12V Dual Polarity PSU Using LM7812 And LM7912 Voltage Regulator ICs.
A ±12V Dual Polarity PSU follows the same schematic layout as that of a general 12V power supply, except of some minor changes. It consists of a step down power transformer that lowers AC from the wall outlet to a desirable range. After that, a rectifying bridge translates the low power AC into a rippling DC. After stamping out any noise from the rectifier output, the DC signal passes through a voltage regulation block that conditions the output DC signal to our desired current and voltage rating.
Hardware Components
You will need the following parts to build this project:
| S.No | Component | Value | Qty |
|---|---|---|---|
| 1) | Step down Transformer | 240V to 15V – 0 -15V, CT, 50Hz | 1 |
| 2) | Voltage Regulators | LM7912, LM7812 | 2 |
| 3) | Diode | 1N4001 | 4 |
| 4) | Capacitors | 2200uF/25V, 10uF/25V | 4 |
| 5) | LED | 5mm, 3.5V | 1 |
| 6) | Resistors | 3.3K Ohms | 1 |
| 7) | Terminal Block Connectors | 3 – Pin | 1 |
| 8) | Soldering Iron | 45W – 65W | 1 |
| 9) | Soldering Wire with Flux | – | 1 |
| 10) | Veroboard | – | 1 |
| 11) | Jumper Wires | – | As per need |
| 12) | Heat Sink | – | 2 |
LM7812 Pinout
LM7912 Pinout
Useful Steps
1) Solder the four 1N4001 diodes in a bridge rectifier configuration on the veroboard.
2) After that, Solder the terminal block connectors for 220V AC input on the Veroboard. Also, solder the bridge rectifier +ve & -ve terminals with the input block connector.
3) Solder the two 2200uF smoothing capacitors on the veroboard.
4) After that, screw the voltage regulators on a heatsink. Also, solder a LED on the veroboard. Connect its +ve terminla with a 3.3K resistor and the -ve terminal with the GND of the circuit.
5) After that solder the voltage regulator ICs on the veroboard.
6) Solder the 10uF capacitors on the veroboard.
7) Solder the output terminal block connector on the veroboard.
8) Connect the 240V to 15V CT transfomer with the input terminal block connector.
9) Power up and test the circuit using a 220V wall outlet.
Circuit Diagram
Working Explanation
The working of this circuit is as follows. Here a 240V to 15V – 0 -15V, CT, 50Hz Step down transformer is being used to lower 220V AC input in to a 15V AC output. This then goes to a bridge rectifier circuit, that translates the 15V AC into a rippling DC. The output from the bridge rectifier then goes through a smoothing filter made out of two 2200uF capacitors, in order to remove any residual noise from the rectifier output.
The output from the smoothing filter is then fed to a general 12V regulator (LM7812) & negative voltage regulator (LM7912) The two voltage regulators ensure a smooth DC output with a constant current load. The ±12V DC signal then passes through another smoothing filter (10uF) in order to remove any remaining noise. The output of the filter then goes to a 3-pin terminal block connector to be taken as an output to drive any DC device.
Applications
- Used by electronic hobbyists in designing various projects.
- Also used in designing small DIY projects.
- Also used in designing small test benches and trainer boards.
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