Control circuit applied to a power converter and operation method thereof

An operation method applied to a brown-out protection, an over-temperature protection, and an over-voltage protection of a control circuit of a power converter, the control circuit comprising a multi-functional pin, a zero-crossing signal generator, an over-voltage detector, a sample and hold unit, a subtractor, a current to voltage converter, a switching circuit, a brown-out detection circuit, a counter, and an over-temperature detection circuit, wherein the multi-functional pin is coupled to a rectifier of the power converter and a thermistor, the operation method comprising:

• the sample and hold unit generating a sampling current according to an input current received by the multi-functional pin, and the brown-out detection circuit or the over-temperature detection circuit executing a first corresponding operation according to an alternating current voltage when a power switch of the power converter is turned on;
• the multi-functional pin receiving an auxiliary current generated by an auxiliary winding of the power converter and the input current when the power switch is turned off;
• the subtractor subtracting the input current received by the multi-functional pin according to the sampling current to filter the auxiliary current, wherein the sampling current is substantially equal to the input current when the power switch is turned off;
• and
• the over-voltage detector or the zero-crossing signal generator executing a second corresponding operation according to the auxiliary current when the power switch is turned off.

An operation method applied to a brown-out protection, an over-temperature protection, and an over-voltage protection of a control circuit of a power converter, the control circuit comprising a multi-functional pin, a zero-crossing signal generator, an over-voltage detector, a sample and hold unit, a subtractor, a counter, and a current to voltage converter, the operation method comprising:

• the sample and hold unit generating a sampling current according to an input current received by the multi-functional pin when a power switch of the power converter is turned on and an alternating current voltage is at a positive half cycle;
• the multi-functional pin receiving an auxiliary current generated by an auxiliary winding of the power converter and the input current when the power switch is turned off;
• the subtractor subtracting the input current received by the multi-functional pin according to the sampling current to filter the auxiliary current when the power switch is turned off, wherein the sampling current is substantially equal to the input current;
• and
• the over-voltage detector or the zero-crossing signal generator executing a third corresponding operation according to the auxiliary current when the power switch is turned off.