Switching-mode power converter and pulse-width-modulation control circuit with primary-side feedback control

A pulse-width-modulation (PWM) control circuit, being applied to a switching-mode power converter with a primary-side feedback control;

• the switching-mode power converter including a transformer, a power switch, a current sensing resistor, and the PWM control circuit;
• the transformer having a primary-side winding, a secondary-side winding, and an auxiliary winding, where a voltage from the auxiliary winding is rectified for outputting a DC feedback voltage;
• the power switch, connected to the primary-side winding in series, being turned on/off by a PWM signal generated from the PWM control circuit;
• the current sensing resistor, positioned between the power switch and a ground level, for transforming a current passing through the primary-side winding into a sensing voltage;
• the PWM control circuit comprising:
• a first sample and hold circuit, for sampling the sensing voltage for a peak value and maintaining the peak value of the sensing voltage at an output terminal of the first sample and hold circuit;
• a second sample and hold circuit, for sampling the sensing voltage for an initial value and maintaining the initial value of the sensing voltage at an output terminal of the second sample and hold circuit;
• an operation processing unit, for subtracting the initial value from the peak value of the sensing voltage to generate an amount of change in the sensing voltage;
• a transconductor circuit, coupled to an output terminal of the operation processing unit, for transforming the amount of change in the sensing voltage into a current signal;
• an error amplifier having two input terminals, one of the input terminals being coupled to the current signal and the feedback voltage and another of the input terminals being coupled to a fixed reference voltage, the error amplifier being utilized for generating an error signal;
• and
• a PWM generator, for determining a duty cycle of the PWM signal according to the error signal.

A switching-mode power converter with a primary-side feedback control, comprising:

• a transformer, having a primary-side winding, a secondary-side winding, and an auxiliary winding, wherein a voltage from the auxiliary winding is rectified for outputting a DC feedback voltage;
• a power switch, connected to the primary-side winding in series and turned on/off by a PWM signal generated from the PWM control circuit;
• a current sensing resistor, positioned between the power switch and a ground level, for transforming a current passing through the primary-side winding into a sensing voltage;
• a sample and hold circuit, for sampling the sensing voltage for a peak value and maintaining the peak value of the sensing voltage at an output terminal of the sample and hold circuit;
• a transconductor circuit, coupled to the output terminal of the sample and hold circuit, for transforming the peak value of the sensing voltage into a current signal;
• an error amplifier having two input terminals, one of the input terminals being coupled to the current signal and the feedback voltage and another of the input terminals being coupled to a fixed reference voltage, the error amplifier being utilized for generating an error signal;
• and
• a PWM generator, for determining a duty cycle of the PWM signal according to the error signal.

A switching-mode power converter with a primary-side feedback control, comprising:

• a transformer, having a primary-side winding, a secondary-side winding, and an auxiliary winding, wherein a voltage from the auxiliary winding is rectified for outputting a DC feedback voltage;
• a power switch, connected to the primary-side winding in series and turned on/off by a PWM signal generated from the PWM control circuit;
• a current sensing resistor, positioned between the power switch and a ground level, for transforming a current passing through the primary-side winding into a sensing voltage;
• a first sample and hold circuit, for sampling the sensing voltage for a peak value and maintaining the peak value of the sensing voltage at an output terminal of the first sample and hold circuit;
• a second sample and hold circuit, for sampling the sensing voltage for an initial value and maintaining the initial value of the sensing voltage at an output terminal of the second sample and hold circuit;
• an operation processing unit, for subtracting the initial value from the peak value of the sensing voltage to generate an amount of change in the sensing voltage;
• a transconductor circuit, coupled to an output terminal of the operation processing unit, for transforming the amount of change in the sensing voltage into a current signal;
• an error amplifier having two input terminals, one of the input terminals being coupled to the current signal and the feedback voltage and another of the input terminals being coupled to a fixed reference voltage, the error amplifier being utilized for generating an error signal;
• and
• a PWM generator, for determining a duty cycle of the PWM signal according to the error signal.