Logic circuit capable of handling large input current

Details Logic circuit capable of handling large input current Logic circuit capable of handling large input current

1995-04-27

1996-07-16

Westin, Edward P.

Electronic digital logic circuitry

Function of and, or, nand, nor, or not

Bipolar transistor

326126, H03K 19082, H03K 1920

Patent

active

055370640

ABSTRACT:
A protection circuit for a semiconductor switch for switching a load is disclosed. Control circuitry is used for switching the semiconductor switch on in response to a switching signal and for switching the semiconductor switch off in response to a deactivation signal. A deactivation circuit is used for generating the deactivation signal. An overvoltage detector circuit responsive to a voltage at an output of the semiconductor switch that exceeds a predetermined value is used for generating an overvoltage signal. The overvoltage detector circuit includes a Zener diode that has its cathode coupled through a resistor to the output of the semiconductor switch and its anode coupled to the collector of the diode connected transistor. A first logic circuit is used for causing the deactivation circuit to generate the deactivation signal in response to the switching signal and the overvoltage signal. The first logic circuit includes a first npn transistor that has its base coupled through a resistor to receive the switching signal. A second npn transistor receives the overvoltage signal through a resistor at its base. The collector of the first npn transistor is coupled to the collector of the second npn transistor. A third npn transistor has its base coupled to the collector of the second npn transistor. A first pnp transistor has its base coupled to the collector of the third npn transistor. One of the two collectors is coupled to the deactivation circuit.

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