SHORT PROTECTION CIRCUIT FOR MAGNETIC-TYPE BALLAST FOR HIGH INTENSITY DISCHARGE LAMP

摘要

PURPOSE: A short protection circuit is provided to prevent an unnecessary power consumption by cutting off the power being supplied to a ballast upon occurrence of short of output terminal. CONSTITUTION: A short protection circuit comprises a short sensing unit for sensing occurrences of short of output terminal of a ballast including an ignitor; and an input control unit for cutting off the voltage being input to a power input(21) in case of short and connecting an input power in case of non-short. The input control unit includes a photo coupler(PC3) for receiving voltages of a condenser(C10) connected to both input terminals of the ballast; an SCR element(Q1) which is turned on/off by the output of the photo coupler, wherein the SCR element has an anode electrode connected to one line of the power input through the solenoid of a relay(RL1) and a cathode electrode connected to the other line of the power input; and a relay switch(SW) which operates by the solenoid of the relay(RL1), and cuts off the input power when the SCR element(Q1) is turned on by the signal output from the photo coupler, and connects the input power to a power line when the SCR element is turned off.