Drive circuit for a field effect-controlled power...

Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Utilizing three or more electrode solid-state device

Utility Patent

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Details

C327S546000, C323S277000, C361S079000

Utility Patent

active

06169441

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention is directed to a drive circuit for a field effect-controlled power semiconductor component.
Drive circuits for metal oxide semiconductor field-effect transistors (MOSFETS) is known. One example of such a drive circuit is disclosed in European Patent Document No. EP 0 822 661. In this example, a control resistor (depletion MOSFET) is switched to high-impedance when the protective circuit is activated and is switched to low-impedance when the protective circuit is deactivated. This depletion MOSFET has an internal gate-source capacitance that, given a positive drive signal at the control input post, charges the drive voltage at the input post and, thus, switches the control resistor, (e.g. the depletion MOSFET) to low-impedance. This condition is maintained as long as the circuit functions normally and no excess current is present. However, if an overload or a short circuit occurs, the excess current limiting circuit is activated. When the current limiting circuit is activated it discharges the internal gate-source capacitance of the depletion MOSFET.
The above-described drive circuit requires a shortened turn-on time during normal operation in comparison to other circuit arrangements. The drive circuit limits the gate-source voltage of the power semiconductor component when a short circuit occurs.
Another example is U.S. Pat. No. 5,506,539. This drive circuit discloses a field-effect controlled power semiconductor component with a controllable resistor that includes two resistors R
3
, R
5
and a transistor Q
2
. A drive signal is supplied to the gate of the power semiconductor component. The drive circuit also includes a controllable component in the form of a power MOSFET Q
4
, that serves the purpose of limiting the gate voltage of the power semiconductor component. The MOSFET is connected between the gate and the source terminal of the power semiconductor component. The drive circuit further contains a protective circuit
10
that drives the MOSFET Q
4
when a non-normal condition of the power semiconductor component
2
occurs. The controllable resistor is switched to high-impedance when the protective circuit is activated or is switched to low-impedance when the protective circuit is deactivated. The controllable resistor of the drive circuit thereby contains an enhancement MOSFET Q
2
.
Additionally, German Specification DE 39 36 544 A1 discloses a circuit arrangement for applications involving a short-circuit of a load that is in series with a power MOSFET. In this example, the drain-source voltage is compared to a reference voltage. When a predetermined value is exceeded, a switch that is positioned between the gate and the source terminal is turned on, this switch discharges the gate-source capacitance of the power MOSFET. At the same time, the switch drives a controllable resistor into a region of a higher impedance reducing the load current of the gate-source capacitance.
SUMMARY OF THE INVENTION
An object of the present invention is to improve a drive circuit for a field effect controlled power semiconductor including a drive signal, a controllable resistor and a protective current limiting circuit.
Another object is to provide a drive circuit arrangement that can be applied both in low-side switches as well as high-side switches.
Another object of the invention is to provide a drive circuit arrangement that can be incorporated in integrated circuit technology.
The present invention provides a drive circuit arrangement for use with field effect controlled power semiconductor component technology.
To this end, in an embodiment of the present invention, a drive circuit includes a voltage source that provides an input signal to the circuit arrangement, a field-effect power semiconductor having a gate, a source and a drain and a protective circuit connected between the drain and the source, the protective circuit is activated when an over voltage is present and provides an output signal. A control circuit receives the output signal from the protective circuit and limits the over voltage at the gate of the power semiconductor. The control circuit is connected between the gate and the source of the power semiconductor. A controllable resistance including an enhancement MOSFET and an external capacitor in which the enhancement MOSFET has a gate and a source and an internal capacitance between the gate and the source. The external capacitor and the internal capacitance are connected in parallel. As a result, the controllable resistance carries the input signal from the voltage source to the power semiconductor so that the controllable resistor is switched to high impedance when the protective circuit is activated and switched to low impedance when the protective circuit is the deactivated.
In an embodiment, an ohmic resistor is connected in parallel to the controllable resistance.
In another embodiment, a switching circuit is connected to the controllable resistance. The switching circuit switches the enhancement MOSFET to low impedance during normal conditions.
In a still further embodiment, the switching circuit includes a resistor and a diode connected in series between the drain and the gate of the enhancement MOSFET.
In another embodiment, the switching circuit includes a second enhancement MOSFET. The second enhancement MOSFET in connected between the drain and the gate of the enhancement MOSFET in the controllable resistance.
In another embodiment, the control circuit includes an enhancement MOSFET and the enhancement MOSFET is driven by the protective circuit and is connected between the gate of the enhancement MOSFET of the controllable resistance and ground.
In a still a further embodiment, the switching circuit is a resistor and a diode connected between the voltage source and the gate of the enhancement MOSFET.
In a still further embodiment, the switching circuit is an enhancement MOSFET whose load path is connected between the voltage source and the gate of the enhancement MOSFET. The enhancement MOSFET of the switching circuit includes a gate that is connected to the voltage source.
These and other objects or advantages of the present invention are described in and are set forth below in the following detailed description of presently preferred embodiments and from the drawings.


REFERENCES:
patent: 5500619 (1996-03-01), Miyasaka
patent: 5506539 (1996-04-01), Kelly et al.
patent: 5801573 (1998-09-01), Kelly et al.
patent: 6019263 (2000-01-01), Tihanyi
patent: 0 882661 (1998-02-01), None

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