Overcurrent protective circuit for modulated-conductivity type MOSFET
First Claim
1. An overcurrent protective circuit including a BIFET having a source, a drain, and a gate connected to an output terminal of a gate signal generating circuit, comprising:
- first voltage detection means for detecting a voltage between the drain and source of said BIFET; and
main switching means for instantaneously lowering a voltage between the gate and source of said BIFET according to the output of said voltage detection means and for preventing the failure of turn-on and the delay of turn-on of said BIFET, comprising;
a thyristor having an anode, a cathode and a gate, said anode connected to the gate of said BIFET;
a first zener diode connected to the gate of said thyristor;
a first MOSFET having a drain connected to the cathode of said thyristor, a source connected to the source of said BIFET, and a gate;
a first resistor means connected between the gate of said first MOSFET and said output terminal of said gate signal generating circuit, said first MOSFET having a gate capacitance which in combination with said first resistor means results in a delay in turn-on of said first MOSFET until after turn-on of said BIFET upon application of a turn-on signal to said output terminal of said gate signal generating circuit.
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Accused Products
Abstract
An overcurrent protective circuit for a modulated conductivity type MOSFET, i.e., a BIFET, which has a voltage detection circuit for detecting a voltage between the drain and source of the BIFET and a main switching circuit for lowering a voltage between the gate ad source of the BIFET and preventing the failure of the BIFET and delay of turn-on of the BIFET according to the output of the voltage detection circuit. The protective circuit produces a constant time delay before the main switching circuit becomes turned on during the initial turn-on period of the BIFET upon application of an ON-gate signal to the gate of the BIFET. The protection circuit thereby prevents, during the initial turn period of the BIFET, a situation where the main switching circuit is turned on but the BIFET is not turned on. The protective circuit further assures that after detection of an overvoltage across the source and drain of the BIFET as may be caused by a load failure, the BIFET gate is maintained at such a low voltage to assure at most a small current conduction through the BIFET even if a ringing voltage occurs across the BIFET.
28 Citations
14 Claims
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1. An overcurrent protective circuit including a BIFET having a source, a drain, and a gate connected to an output terminal of a gate signal generating circuit, comprising:
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first voltage detection means for detecting a voltage between the drain and source of said BIFET; and main switching means for instantaneously lowering a voltage between the gate and source of said BIFET according to the output of said voltage detection means and for preventing the failure of turn-on and the delay of turn-on of said BIFET, comprising; a thyristor having an anode, a cathode and a gate, said anode connected to the gate of said BIFET; a first zener diode connected to the gate of said thyristor; a first MOSFET having a drain connected to the cathode of said thyristor, a source connected to the source of said BIFET, and a gate; a first resistor means connected between the gate of said first MOSFET and said output terminal of said gate signal generating circuit, said first MOSFET having a gate capacitance which in combination with said first resistor means results in a delay in turn-on of said first MOSFET until after turn-on of said BIFET upon application of a turn-on signal to said output terminal of said gate signal generating circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An overcurrent protective circuit including a BIFET having a source, a drain, and a gate connected to an output terminal of a gate signal generating circuit, comprising:
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first voltage detection means for detecting a voltage between the drain and source of said BIFET; and main switching means for instantaneously lowering a voltage between the gate and source of said BIFET according to the output of said voltage detection means and for preventing the failure of turn-on and the delay of turn-on of said BIFET; wherein said main switching means comprises; a first MOSFET having a source, a drain, and a gate connected to the source of said BIFET; a first diode connected between the gate of said BIFET and the drain of said first MOSFET; first resistor means connected between the gate of said first MOSFET and the output terminal of said voltage detection means, said first MOSFET having a gate capacitance which in combination with said first resistor means results in a delay in turn-off of said first MOSFET after a lowering of the drain voltage of said BIFET; and short-circuiting means for short-circuiting the output terminal of said voltage detections means to a predetermined potential during an off-period and a specified intitial turn-on period of said BIFET under the control of an output of said gate signal generating circuit so that turn-on of said BIFET occurs before turn-on of said first MOSFET during said initial turn-on period. - View Dependent Claims (10, 11, 12, 13, 14)
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Specification