26-03-2012, 04:20 PM
Short circuit protection in dc low voltage system
Short circuit protection in dc low voltage system (2).docx (Size: 35.28 KB / Downloads: 61)
In the main power supply circuit, 230V AC is stepped down by transformer X1 (230V AC primary to 0-9V, 300mA secondary), rectified by a fullwave rectifier comprising diodes D1 through D4, filtered by capacitor C1 and regulated by IC 7805 to give regulated 5V (O/P1). Transistors SK100 and BC547 are used to derive the secondary output of around 5V (O/P2) from the main 5V supply (O/P1).
Working of the ShortCircuit Protection circuit is simple. When the 5V DC output from regulator IC 7805 is available, transistor BC547 conducts through resistors R1 and R3 and LED1. As a result, transistor SK100 conducts and short-circuit protected 5V DC output appears across O/P2 terminals. The green LED (LED2) glows to indicate the same, while the red LED (LED1) remains off due to the presence of the same voltage at both of its ends.