Fixed voltage power supply using bridge rectifier

A regulated power supply is vital for any electronic appliance because the semiconductor devices used in them have precise current and voltage ratings. Any deviation from these rating can damage the devices. This circuit supplies a constant DC output derived from the AC mains supply. This project is an improvement over the power supply circuit mentioned earlier. The unregulated DC output is fixed to a constant voltage level by using a voltage regulator. This circuit uses a 7805 linear voltage regulator, capacitors and resistors along with a diode derived bridge rectifier. From providing a fixed voltage supply to making sure that output reaches undisturbed to the device, the diodes and capacitors manage high efficient signal conveyal.

The unregulated DC output produced is sensitive to the fluctuations of the input signal. In this project, to stabilize the output DC against the input variations a voltage regulator IC (78XX) is used in series with the bridge rectifier. XX here denotes the stable voltage level at the output pin of 78XX. To derive a constant 5V output, 7805 is used along with the 6-0-6V, 500mA step down transformer and rectifier. A capacitor C2 (0.1uF) is used to suppress the oscillations if any produced in the regulator IC. C2 is generally used when the regulator IC is far from the power supply filter. Capacitor C4 (35uF) improves the ripple rejection of the regulator by preventing the ripple voltages from being amplified at the output of the regulator. Capacitor C3 (0.1uF) stiffens the output voltage and reduces output impedance. A diode D5 (1N4007) is also used to protect the regulator from damage in case the input gets shorted. If D5 is not provided in the circuit, the output capacitor can dump its charge instantaneously through low impedance paths internal to the regulators.