Minimum on-time reduction method, apparatus, and system using same

1. A minimum on-time reduction method for a switching power conversion, comprising the steps of:

generating a first reset signal according to voltage comparison of a current sensing signal and a reference signal;

generating an over-supply pulse signal according to voltage comparison of said current sensing signal and an up-shifted reference signal;

generating a blanking signal having a blanking period according to a count number of said over-supply pulse signal; and

generating a second reset signal by performing Logic-AND operation on said first reset signal and said blanking signal.

2. The method according to claim 1 , wherein said current sensing signal is generated across a resistor carrying a drain current of an NMOS transistor.

3. The method according to claim 1 , wherein said reference signal is a function of an output error signal of said switching power conversion, and said up-shifted reference signal is derived by shifting up said reference signal with a DC level.

4. The method according to claim 1 , wherein said blanking period is generated according to voltage comparison of a triangle signal and a threshold voltage, wherein said triangle signal has a ramp-up slope proportional to a charging current.

5. The method according to claim 4 , wherein said charging current is proportional to said count number.

6. A minimum on-time reduction apparatus for a switching power conversion, comprising:

a first comparator for generating a first reset signal according to voltage comparison of a current sensing signal and a reference signal;

a second comparator for generating an over-supply pulse signal according to voltage comparison of said current sensing signal and an up-shifted reference signal;

a blanking unit for generating a blanking signal having a blanking period according to a count number of said over-supply pulse signal; and

a Logic-AND gate for generating a second reset signal by performing Logic-AND operation on said first reset signal and said blanking signal.

7. The apparatus according to claim 6 , wherein said current sensing signal is generated across a resistor carrying a drain current of an NMOS transistor.

8. The apparatus according to claim 6 , wherein said reference signal is a function of an output error signal of said switching power conversion, and said up-shifted reference signal is derived by shifting up said reference signal with a DC level.

9. The apparatus according to claim 6 , wherein said blanking unit comprises:

a triangle signal generator, used for generating a triangle signal having a ramp-up slope proportional to a charging current, wherein said charging current is proportional to said count number; and

a third comparator for generating said blanking signal according to voltage comparison of said triangle signal and a threshold voltage.

10. The apparatus according to claim 9 , wherein said triangle signal generator comprises:

a counter, used for generating said count number by counting said over-supply pulse signal;

a charging current generator, used for generating said charging current according to said count number; and

a capacitor, used for generating said triangle signal by coupling to said charging current generator.

11. The apparatus according to claim 10 , wherein said charging current generator comprises a plurality of binary weighted current sources.

12. A system using a minimum on-time reduction apparatus for a switching power conversion, comprising:

a first comparator for generating a first reset signal according to voltage comparison of a current sensing signal and a reference signal;

a second comparator for generating an over-supply pulse signal according to voltage comparison of said current sensing signal and an up-shifted reference signal;

a blanking unit for generating a blanking signal having a blanking period according to a count number of said over-supply pulse signal;

a Logic-AND gate for generating a second reset signal by performing Logic-AND operation on said first reset signal and said blanking signal; and

a power conduction unit, responsive to a PWM signal to provide a power conduction path, wherein said PWM signal is responsive to a set signal and said second reset signal.

13. The system according to claim 12 , wherein said switching power conversion is one selected from the group consisting of AC to DC, AC to AC, DC to AC, and DC to DC.

14. The system according to claim 12 , wherein said switching power conversion is one selected from the group consisting of close loop and open loop.