Working of the circuit is simple to understand, the power supply can be switched ON by pressing the push switch S1, after S1 is pressed the relay switch will become activated and the mains supply will be connected to the circuit. When short circuit will occur at the output of LM317 IC the supply to the 555 IC will be disconnected due to which the relay switch become deactivated and cutoff the mains power going to the circuit, to again start the power supply one should have to press the S1 switch again.
The circuit is built with three ICs which are a 555 timer IC, LE30CZ 3V voltage regulator IC and one LM317 chip that is an adjustable voltage regulator IC. A 230V to 16V step down transformer is used to step down the mains supply and a 3A 50V bridge is used for rectifying the AC voltage. As shown in the circuit the max input voltage to the LM317 should not be increased than 22V. In the place of transformer, bridge and 2200uF capacitor you can also use a 22V 2A plug pack. A suitable heatsink should be used with LM317 IC.
This article describes an adjustable power supply with short circuit switch off function, the circuit will automatically switch of its mains supply when any short circuit occurs in the project connected with the power supply. This power supply is adjustable from 3.5V to 20V DC & the max output current is 1.5A.
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