Power factor correction circuit using reverse sawtooth waves

Details Power factor correction circuit using reverse sawtooth waves Power factor correction circuit using reverse sawtooth waves

1999-05-17

2001-01-23

Wong, Peter S. (Department: 2838)

Electric power conversion systems

Current conversion

With condition responsive means to control the output...

C363S081000, C323S222000

Reexamination Certificate

active

06178104

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority from Korean Priority Document No. 1998-17504, filed on May 15, 1998 with the Korean Industrial Property Office, which document is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power factor correction (PFC) circuit, and more particularly to a PFC circuit using reverse sawtooth waves and controlling slope of the current.
2. Description of the Related Art
A continuous current mode (CCM) control method is commonly used in conventional PFC circuits. Among the different types of CCM control methods for improving the power factor are a peak current control method, a variable hysteresis control method, and an average current control method. Each of these methods has the advantage of being able to obtain a high power factor.
However, the above different types of CCM control methods have serious drawbacks. That is, in the peak current control method, because of the occurrence of external inductor current distortion and dead angle distortion, and the need to maintain a maximum duty at below 50%, control by precise correction is not possible. Also, with the variable hysteresis control method, when input voltage decreases, there is a significant increase in frequencies to control the inductor current. Therefore, the frequency control is limited according to the input voltage. Finally, in the average current control method, very complicated processes are used in trying to obtain a power factor of 1.00, or unity.
SUMMARY OF THE INVENTION
The present invention overcomes the above mentioned problems.
It is an object of the present invention to provide a power factor correction circuit using reverse sawtooth waves, to derive a high power factor correction with a minimal limitation in a duty ratio.
The invention provides a power factor correction circuit comprising a converter, a current detector, an error amplification unit, a comparative wave generator, and a switching driving means.
The converter includes an inductor coupled to an input voltage, a switch controlling the current flowing through the inductor, and a rectifier for rectifying the output voltage of the inductor and supplying the rectified voltage to a load.
The current detector detects the current flowing through the inductor when the switch is turned on.
The error amplification unit includes a first voltage divider for dividing the output voltage of the converter, and an error amplifier amplifying a difference voltage between the divided voltage and a first reference voltage.
The comparative wave generator includes an oscillator generating reverse sawtooth waves and a reference clock signal having a frequency identical to the clock frequency, and in phase with it.
In one aspect, the invention the composite wave generator also includes a multiplier multiplying the output voltage of the error amplifier and a reverse sawtooth waveform by a predetermined gain.
The switching driving means turns off the switch when the output voltage of the current detector is equal to the output voltage of the multiplier, and turns on the switch when the state of the reference clock signal is changed.
In another aspect of the present invention, the comparative wave generator also includes a first subtractor subtracting a second reference voltage from the output voltage of the error amplifier, a second subtractor subtracting the output voltage of the first subtractor from a third reference voltage, a first multiplier multiplying the reverse sawtooth waves and the output voltage of the first subtractor by a first gain, and a second multiplier multiplying the output voltage of the second subtractor and the output voltage of the current detector by a second gain.
The switching driving means turns off the switch when the output voltage of the first multiplier is equal to the output voltage of the second multiplier, and turns on the switch when the state of the reference clock signal is changed.
In the other aspect of the present invention, the comparative wave generator also includes a divider dividing the first gain by the output voltage of the error amplifier, a first multiplier multiplying the reverse sawtooth waves and the output voltage of the error amplifier by a second gain, and a second multiplier multiplying the output of the divider and the output voltage of the current detector by a third gain.
The switching driving means turns off the switch when the output voltage of the first multiplier is equal to the output of the second multiplier, and turns on the switch when the state of the reference clock signal is changed.


REFERENCES:
patent: 3678331 (1972-07-01), Fischman
patent: 5001620 (1991-03-01), Smith
patent: 5003454 (1991-03-01), Bruning
patent: 5804950 (1998-09-01), Hwang et al.

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