Signal transmission circuit for providing control information from secondary side to primary side of power converter, and control circuit for power converter

A control circuit for a power converter, comprising:

• a first control unit, coupled to a secondary-side circuit of the power converter, the first control unit configured to generate a first control signal comprising an on signal and a flag signal, the on signal indicating on-time information for a switch of a primary-side circuit of the power converter, the flag signal indicating whether a predetermined function of the power converter is activated;
• a signal transmission circuit, coupled to the first control unit, the signal transmission circuit comprising:
• a transmitter circuit, configured to generate a ramp signal according to the on signal and the flag signal;
• a signal transformer, coupled to the transmitter circuit, the signal transformer being configured to convert the ramp signal to generate an output signal, wherein when the flag signal indicates that the predetermined function is not activated, the transmitter circuit is configured to generate the ramp signal according to the on signal, and the output signal comprises a positive-going component and a negative-going component occurring one after the other;
• when the flag signal indicates that the predetermined function is activated, the transmitter circuit is configured to generate the ramp signal according to the flag signal, and the output signal comprises one of the positive-going component and the negative-going component consecutively occurring a plurality of times;
• and
• a detection circuit, coupled to the signal transformer, the detection circuit being configured to detect the positive-going component and the negative-going component to generate a second control signal;
• and
• a second control unit, coupled between the detection circuit and the switch, the second control unit configured to control the switch according to the second control signal.