+12V DC Power Supply

Authors: Oyegunle Aisha Motunrayo,  Anumbor Ogor

Introduction

The power supply built in this project coverts a 240v ac to a 12v dc. Production of low voltage DC power supply from AC power is the most important problem faced by many electronics developers. The straight forward technique is the use of a step down transformer to reduce the 230 V or 110V AC to a preferred level of low voltage AC.

Bill of materials

1.      Vero board

2.      Table rectifier

3.      Electrolytic capacitor

4.      7812 voltage regulator

6.      Transformer

Design and Implementation

Power Supply Block Diagram

Schematic Diagram of Power Supply System

The primary windings of the transformer is connected to the non-polarized pin of the rectifier, and the + and – pin of the rectifier is connected to the + and – pin of the electrolytic capacitor respectively. The voltage regulator has three pin (+ – +), the + input pin is connected to the + pin of the capacitor, the – (ground) is connected to the – pin of the capacitor and the third pin (+ output) is the output of the power supply.

Testing the power supply, the secondary windings of the transformer is connected to the AC and using a multimeter placing the + and – rob of the multimeter to the + output of the voltage regulator and the – ground respectively, a 12v output is read.

The power supply unit consists of different components which are explained below:

1. Transformer 24v (300mA): To step down high voltage AC mains to low voltage AC.

Input Signal

Output Signal

2. Rectifier: To convert AC to DC, but the DC output is varying.

 

3. Electrolytic capacitor: To smooth the DC from varying greatly to a small ripple.

4. 7812 voltage regulator: To eliminate ripple by setting DC output to a 12 voltage.

Conclusion and Recommendation

This project was a vast learning experience, and remember do not touch at any points in the circuit because some points are at mains potential. Keep away from touching the points around the dropping capacitor to prevent electric shock, even after switching off the mains. Great care should be taken to construct the circuit since there is no isolation between mains and our circuit. Adequate spacing must be given between the components.