What is a DC Power Supply

A DC power supply is an electronic circuitry that is used to convert an input AC voltage in to a stable output voltage in the form of DC. This circuitry is vastly employed in electronic appliances such as personal computers, washing machines and televisions etc that require a constant DC voltage for their functioning. This circuitry is also used in digital electronic projects where IC’s and microprocessors require a constant DC voltage.

A DC power supply consists of a number of components that work in successive stages to provide the desired DC output level. These stages are described below:-

First of all the input AC voltage is stepped down to a desired level using a transformer. This is achieved due to the difference in the number of turns between the primary and the secondary windings of the transformer. The transformer also provides electrical isolation from the power line which is an important safety factor. The stepped down AC voltage is then fed in to a rectifier circuit. This circuit consists of P-N junction diodes that convert the AC voltage in to a pulsating DC. This conversion is based on the principle that a diode acts as a conductor with a very low resistance when forward biased and acts as an insulator with a very high resistance when reverse biased. This rectification can either be half wave or full wave. Also full wave rectifiers can be of bridge type or centre tap type. The pulsating DC from a rectifier can’t be used in sophisticated electronic appliances as it contains a sufficiently large AC component in addition to the DC component. So this AC component is filtered out by the use of filter circuits. Some of the filter circuits that are employed for this purpose are shunt capacitor circuit, series inductor circuit, L-C filters, R-C filters etc. The filtered output is then fed in to a voltage regulation circuit. The voltage regulation circuit makes the output voltage independent of any fluctuations in load. This circuit can easily be made by the use of a Zener Diode that is operating it in its reverse breakdown region.

Now-a-days more and more sophisticated power supplies can be made by the use of specialized IC’s such as 78XX series, 79XX series etc that results in next to no fluctuation in the output voltage level. There are also microcontroller based supplies that can provide a range of different outputs without any hardware changes in the power supply circuitry.

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