Electricity: power supply or regulation systems – In shunt with source or load – Using a three or more terminal semiconductive device
Reexamination Certificate
2000-11-10
2001-07-17
Sterrett, Jeffrey (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using a three or more terminal semiconductive device
C323S271000, C323S289000
Reexamination Certificate
active
06262564
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to power conversion and, more specifically, to a driver for a controllable switch and a power converter employing the same.
BACKGROUND OF THE INVENTION
A power converter is a power processing circuit that converts an input voltage waveform into a specified output voltage waveform. In many applications requiring a DC output, switched-mode DC—DC converters are frequently employed to advantage. DC—DC converters generally include an inverter, a transformer having a primary winding coupled to the inverter and a rectifier coupled to a secondary winding of the transformer. The inverter generally includes a switching device, such as a field-effect transistor (FET), that converts the DC input voltage to an AC voltage. The transformer then transforms the AC voltage to another value and the rectifier generates the desired DC voltage at the output of the DC—DC converter.
Conventionally, the rectifier includes passive rectifying devices, such as Schottky diodes, that conduct the load current only when forward-biased in response to the input waveform to the rectifier. Passive rectifying devices, however, generally cannot achieve forward voltage drops of less than about 0.35 volts, thereby substantially limiting a conversion efficiency of the DC—DC converter. To achieve an acceptable level of efficiency, DC—DC converters that provide low output voltages (e.g., 1 volt) often require rectifying devices that have forward voltage drops of less than about 0.1 volts. The DC—DC converters, therefore, generally use synchronous rectifiers. A synchronous rectifier replaces the passive rectifying devices of the conventional rectifier with rectifier switches, such as FETs or other controllable switches, that are periodically driven into conduction and non-conduction modes in synchronism with the periodic waveform of the AC voltage. The rectifier switches exhibit resistive-conductive properties and may thereby avoid the higher forward voltage drops inherent in the passive rectifying devices.
One difficulty with using a rectifier switch (e.g., an n-channel silicon FET) is the need to provide a drive signal that alternates between a positive voltage to drive the device into the conduction mode and a zero or negative voltage to drive the device into the non-conduction mode. Of course, depending on the type of rectifier switch, an opposite drive polarity may be employed. Although a capacitive charge within the rectifier switch may only be 30 to 50 nanocoulombs per device (rectifier switch), in situations where as many as a dozen or more devices may be used, a high drive current may be required for a brief period of time to change conduction modes.
Additionally, rectifier switches may require larger voltages than are available from logic circuits, which is typically a maximum of 5 volts, to drive the rectifier switch into the conduction mode. Conventionally, level shifting chips or integrated circuit drivers may be used to solve the problem. However, they typically offer less than an optimal solution since they provide additional product cost and usually cause switching or signal delays that negatively impact the onset of the conduction mode. Additionally, the maximum value of the level shifting voltage may not be satisfactory for some rectifier applications.
Accordingly, what is needed in the art is a driver that minimizes switching delays and provides a broader range of drive signal voltages.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a driver for a controllable switch, a method of driving the controllable switch and a power converter employing the driver or the method. The driver receives a control signal and operates the controllable switch. In one embodiment, the driver includes a switching network coupled to the controllable switch and including first and second complementary drive switches. The driver also includes a capacitor coupled between control terminals of the first and second complementary drive switches and a diode coupled between a bias energy source and the capacitor. The first and second complementary switches cooperate to produce a drive signal as a function of the control signal and a level of the bias energy source.
The present invention introduces, in one aspect, the capability to tailor a value of a drive signal to operate a controllable switch without sacrificing switching response time through switching delays. A plurality of controllable switches may be controlled from a single drive signal employing a single bias energy source. Alternatively, a plurality of bias energy sources may be employed in association with a collection of drivers to accommodate a collection of controllable switches having a spectrum of operating requirements.
In one embodiment of the present invention, a peak of the drive signal is substantially equal to the level of the bias energy source. Of course, the driver may also be appropriately configured to provide a peak of the drive signal that is different than the bias energy source.
In one embodiment of the present invention, the controllable switch is a metal-oxide semiconductor field effect transistor (MOSFET). In a related, but alternative embodiment, the first and second complementary switches are embodied in a complementary metal-oxide semiconductor (CMOS) device.
In one embodiment of the present invention, an input of the driver is coupled to an inverter. Of course, in an alternative embodiment, the input of the driver may accommodate a control signal that does not require an inverter.
In one embodiment of the present invention, the driver further includes a resistor interposed between the diode and the capacitor. Alternatively, the resistor may be interposed between the diode and the bias energy source. In a related, but alternative embodiment of the present invention, the driver further includes a filter capacitor coupled to the bias energy source.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art will appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
REFERENCES:
patent: 5204504 (1993-04-01), Tanaka
patent: 5621604 (1997-04-01), Carlson
patent: 6175218 (2001-01-01), Choi et al.
Lucent Technologies - Inc.
Sterrett Jeffrey
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