DC Regulated Dual Power Supply

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Some electronics circuits require a power supply with pure positive (+Ve) and negative (-Ve) dc outputs as well as zero volts. This is called a dual power supply because it is like two ordinary dc power supplies connected together. Usually, it is a very common requirement in all those circuits that use Op-amps.

In this project, I will show you a regulated dual power supply circuit that generates dual DC outputs from 220-230V AC mains. Depending upon ICs, use the same circuit configuration to produce (+5V, -5V), (+6V, -6V), (+8V, -8V), (+9V, -9V), (+12V, -12V), (+15V, -15V), and (+18V, -18V). Each of the outputs in the circuit has a current delivering capacity of 500mA.

Let's make it!


Components List

The following components are required to make this dual power supply circuit.
  • IC-1 (See the table below)
  • IC-2 (See the table below)
  • C1, C2: 1000uf, 25V electrolytic capacitor
  • C3, C4, C7, C8: 0.1uF ceramic disc capacitor
  • C5, C6: 10uf, 25V electrolytic capacitor
  • D1 to D4: 1N4001 diode
  • T-1: 18V-0-18V, 500mA centre-tapped step down transformer
  • F-1: 1A/250V fuse

Voltage regulator ICs and Outputs

[Select and choose the right voltage regulator ICs for your project.]

IC-1 IC-2 Outputs
7805 7905 +5V, -5V
7806 7906 +6V, -6V
7808 7908 +8V, -8V
7809 7909 +9V, -9V
7812 7912 +12V, -12V
7815 7915 +15V, -15V
7818 7918 +18V, -18V

Circuit Diagram

The schematic of a dc regulated dual power supply circuit is shown below.


Circuit Explanation

The dual power supply circuit is simple which works in four main steps.

Step 1: Steps Down the Mains Power. The circuit consists of a transformer (T-1) that steps down 230V AC to 18V across a center-tapped secondary winding. It is the unregulated AC/DC power supply part of the circuit.

Step 2: Rectification. Diodes D1 to D4 that rectifies AC appearing across the secondary of the transformer. Diodes D1 and D3 providing full-wave rectification to produce positive output, D2 and D4 providing full-wave rectification to produce a negative output.

Step 3: Filtering. Capacitor C1 and C2 providing the filtering action, C3 to C8 are decoupling capacitors.

Step 4: Regulated Fixed Output. Both IC-1 and IC-2 are three-terminal regulators IC (Integrated Circuit) where IC-1 is a fixed output positive regulator and IC-2 is a fixed output negative regulator.


Testing

After, assembling the circuit on a breadboard gives the mains power and then measures the two output regulated voltage with a multimeter.

Now, connect a load to the circuit outputs, you will see that the transformer and the IC regulators do not get excessively heated up, and also will verifies that the regulated fixed outputs voltage stay put.

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