GATE-CHARGE RETAINING SWITCH
The present invention discloses MOSFET or IGBT switch drive circuitry that uses the gate capacitance and the inherently high gate resistance of such switch devices to provide essentially bistable switching. Gate-charge is injected to enhance the switch device(s), invoking an ON state. Gate-charge is removed to deplete the switch device(s), invoking an OFF state. Circuitry is provided to effect charge removal immediately following charge injection, enabling relatively large switch devices to operate efficiently at several MHz. An arrangement for bipolar switch operation is provided.
1 . A substantially bistable power-switch comprising;
at least one gate-charge-retaining power transistor; and
control circuitry responsive to at least one control signal, said control circuitry capable of injecting charge into and removing charge to and from the gate of the power transistor responsive to the control signal,
wherein the power switch is bistable.
2 . The switch of claim 1 wherein two unidirectionally-blocking MOSFET's or IGBT's are arranged to provide bipolar switching.
3 . The switch of claim 1 wherein plural ON signals per OFF signal refresh said switch in the ON state.
4 . The switch of claim 1 wherein plural OFF signals per ON signal refresh said switch in the OFF state.
5 . The switch of claim 1 further comprising one gate drive transformer.
6 . The switch of claim 1 further comprising more than one gate drive transformer.
7 . The switch of claim 6 wherein one gate drive transformer is reset while another is energized.
8 . The switch of claim 3 wherein there is a first power source for the control circuitry, and a second power source, the current of which the switch is controlling, the first and second power sources being independent with the first power source having a lower voltage than the second power source.
9 . The switch of claim 1 wherein, while the switch is on, substantially all of the charge necessary to maintain the power transistor in the ON state is stored within the transistor gate.
10 . The switch of claim 1 wherein the power transistor is a MOSFET or IGBT.
11 . The method of switching a power MOSFET or IGBT comprising;
injecting gate-charge responsive to a control signal to turn ON the MOSFET or IGBT gate-charged power-transistor,
allowing said charge to maintain said MOSFET or IGBT gate-charged power-transistor in an ON state and,
removing said charge responsive to a control signal to turn OFF said MOSFET or IGBT gate-charged power-transistor.
12 . The method of claim 11 wherein the gate charge is injected from a transformer.
13 . A method of controlling a power transistor comprising:
receiving a signal to turn the power transistor on;
providing a pulse of energy to charge the gate of the power transistor, the pulse lasting an amount of time substantially shorter than the on time of the power transistor;
receiving a signal to turn the power transistor off;
discharging the energy stored in the gate of the power transistor.
14 . The method of claim 13 wherein the power transistor is a MOSFET or IGBT.
15 . The method of claim 13 wherein the amount of energy provided in the pulse is approximately equal to the amount of energy necessary to fully charge the gate capacitance of the power transistor.
16 . The method of claim 13 wherein the pulse of energy is provided through a transformer.
17 . The method of claim 13 wherein the power transistor switches a load voltage and the energy pulse has a voltage not greater than the load voltage.