Isolated transformer coupled gate drive for signals having variable duty cycle
AssigneeAvionic Instruments, Inc.
InventorLewis Illingworth
Life of this patent
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Abstract
An improved coupling circuit for use in switched power supplies and other applications utilizes a DC restoration circuit following the secondary stage of a coupling transformer to maintain a relatively constant DC component in the coupled waveform, regardless of its duty cycle. Advantages of the invention include better frequency response, lower noise, and better linearity.
Claims14
A high-frequency drive circuit for controlling the operation of a transistor switching device, comprising:
- a transformer having low-inductance windings, for transforming a primary voltage to a secondary voltage substantially greater than the required output voltage;
- a first low-valued blocking capacitor for coupling an input signal having a first duty cycle to said transformer, wherein said value is selected to permit sudden changes in duty cycle;
- a high-speed DC restoration circuit for receiving said secondary voltage and producing an output signal having a second duty cycle similar to said first duty cycle and a substantially stable DC component, wherein said DC restoration circuit comprises a second low-valued blocking capacitor, a current limiting resistor, and a bipolar limiter.
- an active output buffer for coupling said output signal to the switching transistor.
A method of coupling a signal between first and second isolated circuits comprising the steps of:
- coupling said signal from said first isolated circuit to a primary stage of a transformer;
- coupling said signal from secondary stage of the transformer to a DC restoration circuit;
- coupling said signal from the DC restoration circuit to said second isolated circuit;
- and
- limiting said signal from said DC restoration circuit to said second isolated circuit.
A drive circuit for controlling the operation of a transistor switching device by providing an output signal, comprising:
- a transformer having low inductance windings for transforming a primary voltage to a secondary voltage having amplitude substantially greater than said output signal;
- a first blocking capacitor for coupling an input signal having a first duty cycle to said transformer, wherein the value of said first blocking capacitor is selected to permit sudden changes in duty cycle;
- a high-speed DC restoration circuit for receiving said secondary voltage and producing said output signal having a second duty cycle similar to said first duty cycle and a substantially stable DC component, wherein said DC restoration circuit comprises a second blocking capacitor, a current limiting resistor, and a bipolar limiter;
- and
- an active output buffer for coupling said output signal to said transistor switching device.
A method of coupling a high-frequency signal between an isolated circuit and a transistor switching device, comprising the steps of:
- coupling said high-frequency signal from said isolated circuit to a dc blocking capacitor;
- coupling said high-frequency signal from said dc blocking capacitor to the primary coil of a low-inductance transformer;
- coupling said high-frequency signal from the secondary coil of said transformer to a high-speed DC restoration circuit;
- shaping the waveform of said high-frequency signal to provide an optimal control signal suited to said switching device;
- and
- actively buffering said high-frequency signal from said primary coil of said transformer to said switching device;
- wherein said buffering is provided to enable the minimization of the inductance of the coupling transformer and the capacitance of the DC restoration circuit in order to permit crisp high-frequency switching.
Dependencies are inferred from the claim text.