Electricity: power supply or regulation systems – In shunt with source or load – Using a three or more terminal semiconductive device
Reexamination Certificate
2000-02-25
2001-04-10
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using a three or more terminal semiconductive device
C323S282000, C323S284000, C323S285000
Reexamination Certificate
active
06215288
ABSTRACT:
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for a power converter having a mode of operation in which the converter operates in discontinuous mode at a reduced switching frequency while further providing a control circuit with reduced power requirements and effective DC and transient regulation. The present invention also controls other critical parameters, such as, but not limited to, the minimum switching frequency and maximum peak switch current.
The present invention utilizes a variable frequency mode of operation that provides high efficiencies at low output currents. A power converter according to the present invention is preferably operated in discontinuous mode, and the peak current to which the inductor charges during each switch cycle is varied by the operation of a control circuit. More specifically, a low-power circuit is provided that modulates the peak current trip point to control the switching frequency and drive the converter toward a desired frequency of operation. The peak current trip point and switching frequency are reduced as the output current drops in order to maximize efficiency, but the switching frequency is prevented from dropping below a pre-determined frequency to avoid the generation of noise in the audio range. The peak current and switching frequency are increased as the output current increases, but the peak current automatically asymptotically approaches a pre-determined limit to protect the switching devices from excessive currents. In contrast to the “burst-mode” converter, the converter of the present invention does not require the high bandwidth continuous control loop used during fixed frequency operation, allowing this circuitry to be powered off to reduce quiescent power and increase efficiency at low output currents.
In a preferred embodiment, a converter according to the present invention reduces switching frequency to about 50 KHz, thereby reducing switch drive current from 4 milliAmperes, typically, to about 100 microAmperes. Furthermore, a converter according to the present invention reduces control circuit current draw down from about 600 to 800 microAmperes to about 200 to 300 microAmperes.
In one aspect, a converter according to the present invention modulates the peak switch current to control switching frequency based on a control law curve determined by control circuit elements. This frequency curve can be adjusted by the designer to optimize various operational parameters.
In another aspect, a converter according to the present invention controls the switching frequency and compensates for variations in internal and external components and changes in input voltage/output voltage, thereby extending the useful input voltage range by compensating for nonlinear inductor currents that occur at small input/output voltage ratios.
A converter according to the present invention provides automatic peak current limiting in the power switches without the addition of any additional control circuitry which would draw additional quiescent current. Further, a converter according to the present invention automatically prevents the switching frequency from dropping below a pre-defined level, preventing the converter from generating noise in the audible range.
Additionally, a converter according to the present invention has reduced bandwidth requirements for the control circuitry, which allows the use of low power circuits to reduce quiescent power and increase efficiency.
Thus, the present invention provides a converter having reduced switching frequency to minimize switching losses, and having reduced control circuit power requirements to reduce quiescent losses, while avoiding some problems encountered by other methods.
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Naviasky Eric H.
Ramsey Carl A.
Cadence Design Systems Inc.
Lyon & Lyon LLP
Riley Shawn
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