Patent ID: 8766559

Claim:
A constant power limiter comprising a control circuit and a power source circuit thereof, wherein the control circuit comprises: a voltage detection circuit configured for detecting a voltage of power source; a current detection circuit configured for detecting a load current; a zero-cross detection circuit configured for detecting a zero-cross point of AC power; a load driving circuit comprising a controlled silicon; a micro control unit (MCU) configured for receiving output signals from the voltage detection circuit, the current detection circuit, and the zero-cross detection circuit, and outputting a control signal respectively to the load driving circuit to control a load power, wherein when the load power is less than or equal to a set power value, the load driving circuit has the controlled silicon fully open, when load power is no less than the set power value, the load driving circuit has the controlled silicon conduction angle decreased to stabilize the load power at the set power value; and a bypass circuit connected to an output terminal of the MCU, which is configured for functioning when the control circuit has a breakdown, wherein the bypass circuit comprises a relay and a switch circuit, the relay has a moving contact and a fixed contact serially connected in the circuit, the switch circuit being configured for receiving the control signal from the MCU and control the relay to be pulled in or released according to the control signal.