Switching control circuit for discontinuous mode PFC converters

A PFC converter having a switching control circuit for generating a switching signal coupled to switch an inductor for power factor control, in which the switching control circuit comprising:

• a detection terminal coupled to the inductor to generate a detection signal in response to the discharge of the inductor;
• a ramp generator producing a ramp signal in response to the switching signal;
• a program terminal coupled to the ramp generator to determine the slew rate of the ramp signal and determine the maximum on-time of the switching signal;
• an error amplifier coupled to the output of the PFC converter to generate an error signal for regulating the output of the PFC converter;
• wherein the switching signal is switched on in response to the detection signal;
• and the switching signal is switched off in response to comparison of the ramp signal and the error signal.

A switching control circuit for a PFC converter wherein generating a switching signal coupled for switching an inductor for power factor control, comprising:

• a detection terminal, coupled to the inductor for generating a detection signal in response to the discharge of the inductor;
• an input terminal, coupled for detecting a switching current signal in accordance with the switching current of the inductor;
• a ramp generator, producing a ramp signal in response to the switching signal;
• an error amplifier, coupled to the output of the PFC converter for generating an error signal for regulating the output of the PFC converter;
• a mix circuit, generating a mixing signal proportional to the ramp signal and the switching current signal;
• wherein the switching signal is turned on in response to the detection signal;
• and the switching signal is turned off in response to the comparison of the mixing signal and the error signal.