CIRCUIT FOR REDUCING INRUSH CURRENT GENERATED DURING STARTUP OF A SWITCHING POWER SUPPLY
A circuit for reducing inrush current generated during startup of a switching power supply, which includes a reference voltage generator, an error amplifier, an oscillator, a sawtooth wave generator, a PWM comparator, an overshoot comparator, an AND gate, a R-S flip-flop, a power MOS switch, and a rectifying and filtering circuit. A division voltage outputted from the rectifying and filtering circuit is fed back to the error amplifier.
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The present invention relates to a modification to Pulse Width Modulation (PWM) switching power supply, and particularly to a circuit for reducing inrush current generated during startup of a switching power supply.
BACKGROUND OF THE INVENTION Referring to
The output voltage V0 at startup of the switching power supply is zero, and at this moment the whole loop is not stable. A reference voltage FB-vref generated by the reference voltage generator 1 is transmitted from point D to the terminal “+” of the error amplifier 2, while the terminal “−” of the error amplifier 2 is inputted with the feedback voltage from the division point C of the output voltage V0. Due to the output voltage V0 at startup of the switching power supply is zero, the output of the error amplifier 2 will be high. And then the output of the error amplifier 2 will be inputted to the terminal “−” of PWM comparator 5 so as to be compared with the output of the sawtooth wave generator 4, as shown in
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.
SUMMARY OF THE INVENTIONThe primary objective of the present invention is to provide a circuit for reducing inrush current generated during startup of a switching power supply, comprising: a reference voltage generator, an error amplifier, an oscillator, a sawtooth wave generator, a PWM comparator, an overshoot comparator, an AND gate, a R-S flip-flop, a power MOS switch, and a rectifying and filtering circuit, wherein the reference voltage generator generates a high reference voltage and a low reference voltage, the high reference voltage is inputted to the overshoot comparator, the low reference voltage is inputted to the error amplifier, meanwhile, the division voltage outputted from the rectifying and filtering circuit is fed back to the error amplifier and the overshoot comparator, output of the overshoot comparator and that of the R-S flip-flop are inputted to the AND gate, and then an output of the AND gate is inputted to the power MOS switch.
The present invention will become more obvious from the following description when taken in connection with the accompanying drawings, which show, for purpose of illustrations only, the preferred embodiment in accordance with the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring to
The reference voltage Higher-vref is higher than the reference voltage FB-vref, during startup and before the whole loop is stabilized, the reference voltage Higher-vref is higher than the feedback voltage of the point C, and the output voltage (of point H) of the overshoot comparator 13 is a positive high voltage. Therefore, after the output of the overshoot comparator 13 and that of the R-S flip-flop 6 are inputted to the AND gate 14, the output voltage (at the point B) of the R-S flip-flop 6 can be unchangeably outputted from the AND gate 14 and inputted to the power MOS switch 7, as shown in
While we have shown and described various embodiments in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.
Claims
1. A circuit for reducing inrush current generated during startup of a switching power supply, comprising:
- a reference voltage generator;
- an error amplifier;
- an oscillator;
- a sawtooth wave generator;
- a PWM comparator;
- an overshoot comparator;
- an AND gate;
- a R-S flip-flop;
- a power MOS switch; and
- a rectifying and filtering circuit,
- wherein a division voltage outputted from the rectifying and filtering circuit is fed back to the error amplifier, and the reference voltage generator generates a high reference voltage and a low reference voltage the high reference voltage is inputted to the overshoot comparator, and the low reference voltage is inputted to the error amplifier, and
- wherein the division voltage outputted from the rectifying and filtering circuit is fed back to the error amplifier and the overshoot comparator, an output of the overshoot comparator and an output of the R-S flip-flop are inputted to the AND gate, and an output of the AND gate is inputted to the power MOS switch.
2. (canceled)
Type: Application
Filed: Mar 23, 2005
Publication Date: Sep 28, 2006
Applicant: Princeton Technology Corporation (Hsin Tien)
Inventor: Tu-Hsien Ma (Yonghe City)
Application Number: 11/086,352
International Classification: H02H 7/10 (20060101);