Patent ID: 7518888
Filing Date: 2009-04-14
Classification: H02M

Abstract:
1. A control circuit for a fly-back voltage converter that includes a transformer to transform a primary current in a primary winding into a secondary current in a secondary winding thereof and a switch serially coupled to the primary winding to switch the primary current in response to a control signal, the control circuit comprising: a current detector for detecting the secondary current to produce a detection signal having two states, the detection signal being in a first state while the primary current is switched on and the secondary current is switched off and being in a second state after the secondary current has been switched on, the current detector including a circuit for output of the detection signal initially in the first state and comparing the secondary current with a first threshold value for detecting that the secondary current has been switched on and thereby corresponding to the primary current having been switched off, the circuit outputs the detection signal in the second state responsive to the secondary current exceeding the first threshold value and compares the secondary current with a second threshold value, the circuit returning the output of the detection signal to the first state responsive to the secondary current being lower than the second threshold value to establish a completion of a cycle of the secondary current; and a control signal generator for generating the control signal responsive to the state of the detection signal establishing the completion of the secondary current cycle to then trigger a next on-time cycle for the switch.