Variable Mini DC Power Supply

Variable Mini DC Power Supply

Introduction

A power supply is a hardware component that supplies power to an electrical device. A power supply can be given from the battery or from a hardware circuitry which converts the AC supply into the DC supply or step-down AC to step-up AC and vice-versa. A variable power supply is one which facilitates the user to vary and adjust the desired output voltage and output current. Usually, a potentiometer is used for voltage adjustments. The variable power supply circuit is equipped with an adjustable voltage regulator to adjust the output according to the output. An adjustable voltage regulator has line regulation and load regulation. It is capable of providing 1 amps with voltage ranging from 1.25 volts to 30 volts.

Circuit diagram

Variable mini dc power supply

Components required

• IC – LM317 – 1no
• Diode – 1N4007 – 4nos
• Capacitor – 3300uf/50v – 1no
• Capacitor – 1uf/50v – 1no
• Capacitor– 10uf/50v – 1no
• Resistor – 3.3k – 1no
• Resistor – 240ohm – 1no
• Variable resistor – 5k – 1no
• LED – 5mm,RED – 1no
• Transformer – 230/12-0-12,1A – 1no

How the circuit works

The voltage from the step-down transformer is then fed to the bridge rectifier which generates a continuous pulsating DC signal.

The polarity of the output cannot be inverted and has large ripples in it. This pulsating DC also has some unwanted current (ripples) which makes it impossible for using in powering applications.

A smoothing capacitor which acts as a filter is used to remove unwanted current (Ripples) and the output with capacitance further filtered to get pure DC.

The smooth, non-pulsating DC signal is fed to the voltage regulator LM317 is used as a voltage regulator. The capacitors C2 and C3 are used to eliminate the ripples if the filtering process is done away from the regulator. Capacitor C3 also prevents the  LM317 voltage regulator to act as an oscillator.

LM317 pin configuration