PWM controller regulating output voltage and output current in primary side

A PWM controller for regulating an output voltage and an output current in a primary side circuit, the PWM controller comprising:

• a feedback synthesizer for generating a feedback voltage in response to a supply voltage, wherein the supply voltage is supplied by an auxiliary winding of a transformer for powering the PWM controller;
• wherein the feedback voltage varies in inverse proportion to the supply voltage;
• an adaptive load circuit for producing an adaptive load current to keep a supply current as a constant by means of compensation, wherein the supply current is sourced by the supply voltage for powering the PWM controller;
• a programmable power limiter for generating a limit voltage, wherein the limit voltage varies in direct proportion to the supply voltage;
• an oscillator for outputting a pulse signal;
• a first AND-gate having a first input terminal, a second input terminal and an output terminal;
• a RS flip-flop for generating an on-off signal, wherein the RS flip-flop is set by the pulse signal and reset by an output of the first AND-gate;
• a second AND-gate having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal of the second AND-gate is supplied with the pulse signal, the second input terminal of the second AND-gate is supplied with the on-off signal, and the output terminal of the second AND-gate supplies a PWM signal for switching the transformer;
• a first comparator having a positive input terminal, a negative input terminal and an output terminal, wherein the positive input terminal of the first comparator is supplied with the feedback voltage, and the negative input terminal of the first comparator is supplied with a current-sense voltage, wherein the current-sense voltage is converted from a switching current of the transformer;
• and
• a second comparator having a positive input terminal, a negative input terminal and an output terminal, wherein the positive input terminal of the second comparator is supplied with the limit voltage and the current-sense voltage is supplied to the negative input terminal of the second comparator, wherein an on-time of the PWM signal increases in direct proportion to the feedback voltage wherein the on-time of the PWM signal decreases in direct proportion to the limit voltage.