High-Speed Reflected Signal Detection for Primary-Side Controlled Power Converters

A controller for a power converter, comprising:

• a switching circuit, generating a switching signal to drive a transformer in response to a detection signal from said transformer for regulating said
• a discharging circuit, coupled to a supply terminal of said controller, wherein said controller is powered by a reflected signal of said transformer via said supply terminal of said controller, said discharging circuit is coupled to discharge a current sourced from said supply terminal of said controller during an off-period of said switching signal.

A clamping circuit for increasing a detecting speed for a reflected signal from a transformer, comprising:

• a comparison circuit, comparing a detection signal with a threshold voltage for generating a level-control signal;
• and
• a transistor, coupled to said comparison circuit for clamping a maximum level of said detection signal in response to said level-control signal.