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Variable power supply


Himanshu Choudhary



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 project about 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 circuit is made using following active and passive electronic components:

1.     Bridge Rectifier

2.     Resistors

3.     Capacitors

4.     Variable Resistors.

5.      Linear Voltage Regulator IC





In this project, 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


Capacitor image

Capacitor is a passive component used to store charge. The charge (q) stored in a capacitor is the product of its capacitance (C) value and the voltage (V) applied to it. Capacitors offer infinite reactance to zero frequency so they are used for blocking DC components or bypassing the AC signals. The capacitor undergoes through a recursive cycle of charging and discharging in AC circuits where the voltage and curre...

Presets | Variable Resistors
A preset is a three legged electronic component which can be made to offer varying resistance in a circuit. The resistance is varied by adjusting the rotary control over it. The adjustment can be done by using a small screw driver or...
1N4001 Diode Image
Diode 1N4001

1N4001 is a member of 1N400x diodes. Diode is a rectifying device which conducts only from anode to cathode. Diode behaves open circuited for the current flow from cathode to anode. 1N4001 is a 1A diode with low forward voltage drop and high surge current capability. It comprises of diffused PN junction and has low reverse leakage current of 5µA. Its DC blocking voltage is 50V.



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