Current feedback method, current feedback circuit, driving circuit and switching power supply thereof

A current feedback driving circuit for a switching power supply, the current feedback driving circuit comprising:

• a) a first current mirror circuit having an input terminal coupled to a source of a main power transistor of said switching power supply, and a control terminal configured to receive a pulse-width modulation (PWM) control signal, said first current mirror circuit being configured to generate a first mirror current;
• b) said first current mirror circuit comprising first and second transistors having gates coupled to said PWM control signal and sources coupled to ground, wherein a drain of said first transistor is coupled to said source of said main power transistor, and a drain of said second transistor is coupled to a current detection pin, wherein said first and second transistors and said main power transistor are on when said PWM control signal is active;
• c) said first current mirror circuit and said main power transistor being on such that an output sampling current flows through said first current mirror circuit and said main power transistor when said PWM control signal is active;
• d) a second current mirror circuit configured to generate an output feedback current that is in a predetermined direct proportion with said output sampling current, and is generated in accordance with said first mirror current, wherein said output feedback current flows through said current detection pin;
• e) a first switch circuit comprising an inverter coupled between said PWM control signal and a gate of a third transistor having a drain coupled to a non-inverting input terminal of an operational amplifier, and a source coupled to ground, wherein said first switch circuit is on when said PWM control signal is inactive;
• and
• f) a PWM control signal generation circuit configured to generate said PWM control signal in accordance with said output feedback current.

A method of controlling a current feedback circuit, the method comprising:

• a) receiving, by a first current mirror circuit, a pulse-width modulation (PWM) control signal, said first current mirror circuit comprising first and second transistors having gates coupled to said PWM control signal and sources coupled to ground, wherein a drain of said first transistor is coupled to a source of a main power transistor, and a drain of said second transistor is coupled to a current detection pin, wherein said first and second transistors and said main power transistor are on when said PWM control signal is active;
• b) turning on said first current mirror circuit and said main power transistor of a switching power supply such that an output sampling current flows through said first current mirror circuit and said source of said main power transistor when said PWM control signal is active;
• c) generating, by a second current mirror circuit, an output feedback current in a predetermined direct proportion to said output sampling current, wherein said output feedback current flows through said current detection pin;
• and
• d) providing said output feedback current to said current detection pin, wherein said current feedback circuit comprises a first switch circuit having an inverter coupled between said PWM control signal and a gate of a third transistor, said third transistor having a drain coupled to a non-inverting input terminal of an operational amplifier, and a source coupled to ground, wherein said first switch circuit is on when said PWM control signal is inactive.