Patent ID: 7598680

Claim:
An electric power protection circuit coupled in series with a secondary side circuit of a transformer in a switch mode power supply, comprising: a voltage/current limiting device to get an electric power signal output from the secondary side circuit of the transformer in the power supply that goes through current and voltage limitation before being output; and a constant current/voltage controller to get the electric power signal after having the current and voltage limited by the voltage/current limiting device that is controlled at a constant voltage and a constant current to achieve electric power protection, wherein the voltage/current limiting device is a diode and has a negative electrode connecting to an output commutation filter device in the switch mode power supply and a positive electrode connecting to the constant current/voltage controller; and wherein the constant current/voltage controller comprises: a first comparator which has a negative input end forming a constant voltage control end and a positive input end connecting to a voltage source and an output end delivering a constant voltage control signal; and a second comparator which has another negative input end forming a constant current control end and another positive input end connecting to the voltage source through a voltage dividing circuit, and another output end connecting to the output end of the first comparator to output a constant voltage control signal; the another positive input end connecting to a first output end of the voltage dividing circuit which has a second output (input) end to output (input) a constant current control signal.