How to design a 5V / 9 V / 12V Power supply


learn how to design a 5v dc power supply, 9 v dc power supply or 12 v dc power supply with block diagram & circuit diagram of dc power supply. After this tutorial you will be able to design a DC power supply at your home or College lab.

First of all, we discuss about why we need 5 V, 9V or 12 V power supply?

Every circuit runs on a different voltage, some circuits runs on 1.5V, 5V, 9V and so on. Generally mostly circuits uses the voltage of 5V, 9V, 12V.  If we are using a ATMega 16 micro controller then we need a 5 V power supply because the operating voltage for ATMEGA 16 micro controller is 5 V. If you will give voltage greater than 5 V than your micro controller may get damaged. So for avoiding this we always use a 5 V power supply for micro controller circuits.

Same condition with other dc equipment that runs on 9 V or 12 V. So we have to provide the power supply according to the running voltage of circuit or equipment.

Designing of dc power supply :

Below is a block diagram of dc power supply in which four steps are given named as:

  1. Transformer ( Stepping Down)
  2. Rectifier ( ac to dc conversion)
  3. Filter ( Removing ripples from dc current)
  4. Voltage Regulator ( To set regulated dc supply)
Power supply block diagram
Power supply block diagram

Stepping down voltage:-First step is is scale down the voltage by a step down transformer. A step down transformer converts the 220 ac voltage to the lower ac voltage. Now clear a doubt: – Maximum people thinks that a transformer give dc output voltage because we don’t get shock by touching its output wire. But this is totally wrong. A step down transformer gives ac (alternating current ) at output.

Rectifier: These are the equipment  that converts the alternating current into direct current. The process of conversion from ac (alternating current) to dc (direct current) is known as rectification. These are very important circuits in the designing the dc power supply.

Bridge rectifier circuit
Bridge rectifier circuit

In our power supply we are using full wave bridge rectifier. This rectifier is made up of 4 pn-junction diodes. The simple diagram of rectifier circuit is shown in figure below

Filter :- After rectification a filtering process of dc current is carried out with the help of filter because the output of the Rectifier contains some ripples or you can say distortion. So we need to filter these distortions. In our power supply we are using a 50 V 1000 uF capacitor. You can also use a 25 V 1000uF or 35 V 1000 uF capacitor instead of 50 V 1000uF capacitor.

Voltage Regulator IC :- Voltage regulator provides the regulated output. There are many voltage regulator ICs available in the market. For 5V dc output we are using LM7805, for 9 V dc power supply we are using LM7809, for 12 V dc power supply we are using LM7812.

Voltage regulator with pin discription
Voltage regulator with pin discription

Now arrange your components according to the circuit as shown below and solder them on pcb board. For testing connect a LED at the end of the circuit with 330 ohm resistor.

Power supply circuit diagram
Power supply circuit diagram

How to design a 5 V, 9V and 12 V dc power supply

Change the voltage regulator according to your need. You can also use more than 1 voltage regulator ic in a single circuit. Use higher output IC before the lower output IC and make a variable dc power supply with the help of voltage regulator ICs


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