SYSTEM PROTECTING CIRCUIT OF SMPS

摘要

PURPOSE: A system protecting circuit of SMPS is provided to detect whether a current flowing through an output end of a switching device is an over current and stop the operation of the switching device if the detected current is an over current. CONSTITUTION: A system protecting circuit of SMPS comprises a comparator(C1), a signal passing section(100), and AND gate(200), and a SR latch(FF). The non-converting input of the comparator(C1) is the voltage(Vsen) detected by a current detecting resistance(Rsen), and the converting input of the comparator(C1) is a predetermined standard voltage(Vth). The standard voltage(Vth) is higher than the voltage detected when an NMOS transistor(M1) is turned on. The input of the signal passing section(100) is an oscillating clock(CK).