Things we need...
- General Purpose Diode x 4
- 100 uF Capacitor x 1
- Linear Voltage Regulator LM7805 x 1
- Step down transformer x 1
- 10 nF Capacitor x 1
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Step 1: Step Down AC Voltage
The mains supply which comes to our house is usually 220V-240V. Firstly, we need to step-down the voltage to 12V using from 220V using a 12-0-12 step-down transformer. In the transformer, there are primary and secondary coils which step up or step down the voltage according to the no of turn in the coils.
Selection of proper transformer is very important. The current rating of a transformer depends upon the requirement of the load circuit. Mind that the voltage rating should be more than the required voltage. Means if we need 5V DC, the transformer should be at least of 7V, because of voltage regulator IC 7805 drops about 2V for the voltage regulation.
Step 2: Rectification
Rectification is the process of removing the negative part of the AC and only give positive part of AC. Thus, it produces the pulsating DC. This can be achieved using 4 P-N junction diodes. Diodes are unidirectional i.e. they only allow current to flow in one direction. In first half cycle of AC, diode D2 & D3 are forward biased and D1 and D4 are reversed biased, and in the second half cycle (negative half) Diode D1 and D4 are forward biased and D2 and D3 are reversed biased. This Combination converts the negative half cycle into positive.