Power converter for compensating maximum output power and PWM controller for the same
View Patent ↗A PWM controller compensates a maximum output power of a power converter, and includes a PWM unit and a compensation circuit. The PWM unit generates a PWM signal for controlling a power switch to switch a power transformer, which has a primary winding connected to the power switch and is supplied with an input voltage of the power converter. A pulse width of the PWM signal is correlated to an amplitude of the input voltage. The compensation circuit generates a current boost signal in response to the PWM signal by pushing up a peak value of a current-sense signal generated by a current-sense device in response to a primary-side switching current of the power transformer. A peak value of the current boost signal is adjusted by the pulse width of the PWM signal for compensating a difference of the maximum output power caused by the amplitude of the input voltage.
1. A PWM controller for compensating a maximum output power of a power converter, comprising:
a PWM unit for generating a PWM signal for controlling a power switch to switch a power transformer, wherein the power switch is coupled to a primary winding of the power converter, the power transformer is supplied with an input voltage of the power converter, and a pulse width of the PWM signal is correlated to an amplitude of the input voltage; and
a compensation circuit coupled between the PWM unit and a current-sense device for generating a current boost signal in response to the PWM signal and a current-sense signal, wherein the current-sense signal is generated by the current-sense device in response to a primary-side switching current of the power transformer, the current boost signal is generated by pushing up a peak value of the current-sense signal, and a peak value of the current boost signal is adjusted by the pulse width of the PWM signal for compensating a difference of the maximum output power caused by the amplitude of the input voltage.
2. The PWM controller of claim 1 , wherein the compensation circuit comprises:
an integrated circuit for generating an compensation signal for integrating an inverted PWM signal from the PWM unit, wherein the inverted PWM signal is generated in response to the PWM signal through an inverting circuit, and the compensation signal has a DC level proportional to a pulse width of the inverted PWM signal; and
a boost circuit coupled between the integrated circuit and the current-sense device to push up the current-sense signal for generating the current boost signal, wherein the current boost signal is equal to the compensation signal plus the current-sense signal.
3. The PWM controller of claim 2 , wherein the boost circuit comprises:
a voltage-to-current converter coupled to the integrated circuit for converting the compensation signal into a current signal; and
a boost device coupled between the voltage-to-current converter and the current-sense device for generating the current boost signal in response to the current signal and the current-sense signal.
4. The PWM controller of claim 3 , wherein the boost device comprises a resistor.
5. The PWM controller of claim 2 , wherein the boost circuit comprises an adder coupled between the integrated circuit and the current-sense device for generating the current boost signal in response to the compensation signal and the current-sense signal.
6. The PWM controller of claim 1 , wherein the pulse-width of the PWM signal is decreased in response to an increase of the input voltage, and the pulse-width of the PWM signal is increased in response to a decrease of the input voltage.
7. A power converter for compensating a maximum output power, comprising:
a power switch coupled to a primary winding of the power converter for switching a power transformer supplied with an input voltage of the power converter;
a PWM unit for generating a PWM signal for controlling a power switch, wherein a pulse width of the PWM signal is correlated to an amplitude of the input voltage;
a current-sense device for generating a current-sense signal in response to a primary-side switching current of the power transformer; and
a compensation circuit coupled between the PWM unit and the current-sense device for generating a current boost signal in response to the PWM signal and the current-sense signal, wherein the current boost signal is generated by pushing up a peak value of the current-sense signal, and a peak value of the current boost signal is adjusted by the pulse width of the PWM signal for compensating a difference of the maximum output power caused by the amplitude of the input voltage.
8. The power converter of claim 7 , wherein the compensation circuit comprises:
an integrated circuit for generating an compensation signal for integrating an inverted PWM signal from the PWM unit, wherein the inverted PWM signal is generated in response to the PWM signal through an inverting circuit, and the compensation signal has a DC level proportional to a pulse width of the inverted PWM signal; and
a boost circuit coupled between the integrated circuit and the current-sense device to push up the current-sense signal for generating the current boost signal, wherein the current boost signal is equal to the compensation signal plus the current-sense signal.
9. The power converter of claim 8 , wherein the boost circuit comprises:
a voltage-to-current converter coupled to the integrated circuit for converting the compensation signal into a current signal; and
a boost device coupled between the voltage-to-current converter and current-sense device for generating the current boost signal in response to the current signal and the current-sense signal.
10. The power converter of claim 9 , wherein the boost device comprises a resistor.
11. The power converter of claim 8 , wherein the boost circuit comprises an adder coupled between the integrated circuit and the current-sense device for generating the current boost signal in response to the compensation signal and the current-sense signal.
12. The PWM controller of claim 7 , wherein the pulse-width of the PWM signal is decreased in response to an increase of the input voltage, and the pulse-width of the PWM signal is increased in response to a decrease of the input voltage.