Variable power supply

The electronic devices are very sensitive to the fluctuations in the power fed to them. This problem can be solved by using regulated power supply for them. This power supply circuit is equipped with an adjustable voltage regulator to adjust the output in accordance with the requirement. Adjustable voltage regulators have both line and load regulation which is better than standard fixed regulators..

The stepped down AC from the secondary winding of the transformer is fed to the bridge rectifier for rectification. The output has pulsating DC which is filtered by a capacitor C1 (1000uF). This output needs to be stabilized against the input variations by using a voltage regulator IC (LM317) in series with the bridge rectifier.

 This regulator not only guarantees stable output but can also be adjusted to obtain a desired level of voltage output. The output from the regulator can be varied from 1.2V to 25V. This is achieved by adjusting the value of variable resistor (preset) VR1 (5k). A fixed resistor R1 (220) along with VR1 forms a potential divider. A capacitor C2 (0.1uF) is used to suppress the oscillations, if any, produced in the voltage regulator.

Circuit Diagram

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