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This 30v variable power supply circuit is based on LM317  voltage regulator circuit . This LM317 30v variable power supply circuit can deliver high current (around 5 amps) and variable output voltage between 1.2 volts, up to 30 volts. The led D3 mounted on pin 6 at lm301 lights in constant current mode . 30V Variable Power Supply Using LM317 Circuit diagram  Current limit can be adjusted using R2 potentiometer and the output voltage can be adjusted from 1.2 volts to 30 volts using R8 potentiometer . Input voltage for this variable power supply must be around 35 volts .For this power supply circuit you need to use LM317K circuit (in to3 package ) which must be mounted on a heatsink .

This is a project of 1.2-30V/1.5A Variable Regulated Power supply, This is simple 1.2-30V/1.5A variable regulated power supply circuit diagram The 110V-AC coming from the powercord is fed to the transformer TR1 via the on-off switch and the 500mA fuse. The 30vac output (approximately) from the transformer is presented to the BR1, the bridge-rectifier, and here rectified from AC (Alternating Current) to DC (Direct Current). If you don't want to spend the money for a Bridge Rectifier, you can easily use four general purpose 1N4004 diodes. The pulsating DC output is filtered via the 2200µF capacitor (to make it more manageable for the regulator) and fed to 'IN'-put of the adjustable LM317 regulator (IC1). The output of this regulator is your adjustable voltage of 1.2 to 30volts varied via the 'Adj' pin and the 5K potmeter P1. The large value of C1 makes for a good, low ripple output voltage.  1.2-30V/1.5A Variable Regulated Power supply Circuit Diagram Why exactly 1.2V...