THE PROTECTING DEVICE OF THE POWER SUPPLY CIRCUIT

A protecting device of a switching mode power supply circuit is provided to stop the operation of power supply circuit compulsorily by detecting abnormal current due to short in an output terminal of floated coils unconnected to a chassis ground of a secondary transformer. In a protecting device of a switching mode power supply circuit, a rectifying unit(104) rectifies AC power(100) to DC voltage. A transforming unit transforms the DC voltage of the rectifying unit(104) by different coil winding ratios of a primary transformer(108) and a secondary transformer(110) and has primary and secondary side coils connected to a chassis ground and floated coils(F(+),F(-)) unconnected to the chassis ground. A detecting unit(120) detects the voltage level of the secondary side coil connected to the chassis ground of the transforming unit and detects abnormal current due to short of the floated coils(F(+),F(-)). A short detecting unit(114) transmits the abnormal current due to short of the floated coils(F(+),F(-)) by being connected between the floated coils(F(+),F(-)) and the detecting unit(120). A switching IC(106) intercepts the supply of voltage to the primary side transformer according to the detection of abnormal current of the floated coils(F(+),F(-)) transmitted from the short detecting unit(114).