Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
2002-12-27
2004-06-01
Riley, Shawn (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
C363S132000, C363S041000
Reexamination Certificate
active
06744649
ABSTRACT:
BACKGROUND OF INVENTION
Field of Invention
The present invention relates in general to a pulse width modulation (PWM) power converter, and more particularly, to a pulse width modulation power converter using zero voltage switching technique and power saving means.
Power converters have been frequently used to convert an unregulated power source into a constant voltage source. Transformers having a primary winding and a secondary winding are the hearts of most power converters. Typically a switching device is connected to the primary winding to control energy transferred from the primary winding to the second winding and output therefrom. Currently, under the control of the switching device, the pulse width modulation power converter can be operated at a constant high frequency with reduced size and weight. However, such a power converter suffers from the issues of switching loss, component stress and noise, and electromagnetic interference (EMI).
To resolve the switching loss problem of the pulse width modulation power converters, a phase-shift scheme for soft switching operation has been proposed, particularly for the high-frequency power conversion. For example, the full-bridge (FB) quasi-resonant zero-voltage switching (ZVS) technique has been disclosed in U.S. Pat. No. 4,855,888, “Constant frequency resonant power converter with zero-voltage switching”, issued to Christopher P. Henze, Ned Mohan and John G. Hayes at Aug. 8, 1989, U.S. Pat. No. 5,442,540, “Soft-switching PWM converters” issued to Guichao C Hua and Fred C. Lee at Aug. 15, 1995, and “Soft-switched full-bridge converters” disclosed by Yungtaek Jang and Milan M. Jovanovic at Mar. 12, 2002. In U.S. Pat. No. 5,973,939, “Double forward converter with soft-PWM switching” issued to F. Don Tan at Oct. 26, 1999 and U.S. Pat. No. 6,191,960, “Active clamp isolated power converter and method of operating thereof” issued to Simon Fraidlin and Anatoliy Polikarpov at Feb. 20, 2001, the active clamp technique has been employed in the forward zero-voltage switching power converters. In U.S. Pat. No. 6,069,798, “Asymmetrical power converter and method of operation thereof” issued to Rui Liu at May 30, 2000, an asymmetrical scheme has been developed for a half-bridge (HB) topology.
Among various zero-voltage switching power converters, a parasitic leakage inductor of the transformer or at least one additional magnetic component is used as a resonant inductor or switch to generate a circulating current, so as to achieve the zero-voltage transition and switching operation. The parasitic leakage inductor of the transformer or the additional magnetic component, though providing the aid of zero-voltage transition and switching, consequently increases switching stress and noise.
Further, in such an approach, power consumption caused by circulating current is significantly high in the light load or zero-load condition.
SUMMARY OF INVENTION
The present invention provides a zero-voltage switching pulse width modulation power converter for high frequency operation. The zero-voltage switching pulse width modulated power converter is operated at a constant high frequency with low switching loss, low stress, and low noise.
The present invention further provides a zero-voltage switching pulse width modulation power converter that can realize a zero-voltage transition and switching operation without using an additional magnetic device or leakage inductor of the transformer.
The present invention also provides a zero-voltage switching pulse width modulation power converter that consumes relatively low power in the light load and zero-load conditions.
Further, the present invention provides a control scheme to optimize soft switching of a power converter.
The zero-voltage switching pulse width modulation power converter provided by the present invention comprises a transformer, a primary circuit, and a secondary circuit. The transformer has a primary winding coupled to the primary circuit and a secondary winding coupled to the secondary circuit. The zero-voltage switching pulse width modulation further comprises a feedback circuit, coupled to an output of the secondary circuit to generate a feedback voltage. The primary circuit further comprises a controller coupled to the feedback voltage. The controller is operative to conduct the primary winding to an input voltage source in response to the feedback circuit. In addition, the primary circuit further comprises a pair of main switches and a pair of auxiliary switches.
The soft-switching power converter further comprises a timing resistor coupled to the controller to adjust a pulse width of the second switching signal, a programming resistor coupled to the controller to determine a pulse width of the second switching signal as a function of a load of the power converter, and the controller may further comprise a reference resistor to determine a switching frequency of the power converter.
The controller is operative to generate the first and the second switching signals, such that each switching cycle of the power converter comprises four operation stages. In the first operation stage, the controller conducts the input voltage source and the primary winding via the main switches by generating the first switching signal. In the second operation stage, the controller switches off the first switching signal. In the third operation stage, the controller generates a second switching signal to conduct the input voltage source to the primary winding via the auxiliary switches. In the fourth operation stage, the second switching signal is switched off.
The present invention further provides a controller comprising an oscillator, an inverter, first to second comparators, first to third D-type flip-flops, and a first AND gate and a second AND gate. The oscillator is operative to generate a clock signal, a ramp signal and a saw signal. The inverter has an input terminal receiving the clock signal and an output terminal. The first comparator has a positive terminal connected to a feedback voltage obtained from an output voltage of the power converter, a negative terminal coupled to the ramp signal, and an output terminal. The second comparator has a positive terminal coupled to a variable current, a negative coupled to the saw signal, and an output terminal. A variable current flows through the timing resistor form the variable voltage that compares with the saw signal to produce a signal for generating the second switching signal. The first D-type flip-flop is coupled to the output terminals of the inverter and the first comparator and a voltage source. The first D-type flip-flop further comprises an output. The second D-type flip-flop is coupled to the output terminals of the inverter and the second comparator and the voltage source, and the second D-type flip-flip further comprises an output. The third D-type flip-flop is coupled to the output terminal of the inverter, and the third D-type flip-flop has a first output and a second output inverted from the first output. The first output of the third D-type flip-flop output a first enable signal for the first switching signal. The second output of the third D-type flip-flop output a second enable signal for the second switching signal. The first AND gate is coupled to the outputs of the first D-type flip-flop and the inverter, and the first enable signal. The second AND gate is coupled to the outputs of the second D-type flip-flop and the inverter, and the second enable signal. The first AND gate generates a first switching signal to drive the main switches, and the second AND gate generates the second switching signal to drive the auxiliary switches.
The controller further comprises a variable current source to generate the variable current. The variable current source comprises a programmable current, an I/V resistor, an op-amplifier, a constant current source, a pair of mirrored transistors and a transistor. The programmable current flowing through the I/V resistor generates a voltage that is connected to the positive input terminal of the op-amplifier.
Chen Chern-Lin
Lin Jenn-yu G.
Yang Ta-yung
Jiang Chyun IP Office
System General Corp.
LandOfFree
Zero switching power converter operable as asymmetrical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Zero switching power converter operable as asymmetrical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Zero switching power converter operable as asymmetrical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3357681