Transistor protection circuit

An arrangement for protecting a semiconductor device from electrical stress damage due to spurious high voltage transients, said semiconductor device comprising a semiconductor junction coupled to a circuit point at which said transients may appear and susceptible of damage from electrical stress when said transients exceed a given level, said protecting arrangement comprising:

• a protection transistor with a collector electrode coupled to an operating potential, a base electrode, and an emitter electrode coupled to said circuit point;
• means for applying a reference bias voltage to said base electrode for reverse biasing the collector-base junction of said protection transistor, and to provide reverse biasing of the base-emitter junction of said protection transistor in the absence of said transients so as to render said protection transistor normally nonconductive, the level of said reference bias voltage being such that the base-emitter junctionof said protection transistor is forward biased in response to transients exceeding a threshold level below said given level to permit conduction in the emitter-collector path of said protection transistor to divert transient currents away from said semiconductor device;
• and wherein
• said emitter of said protection transistor is connected to said semiconductor device with substantially zero offset voltage between said circuit point and said semiconductor device.

An arrangement for protecting a semiconductor device from electrical stress damage due to spurious high voltage transients, said semiconductor device comprising a semiconductor junction coupled to a circuit point at which said transients may appear and susceptible of damage from electrical stress when said transients exceed a given level, said protecting arrangement comprising:

• a protection transistor with a collector electrode coupled to an operating potential, a base electrode, and an emitter electrode coupled to said circuit point;
• means for applying a reference bias voltage to said base electrode in such manner that the bias of said base electrode is determinable independent of bias of said semiconductor device and bias at said circuit point, said reference bias voltage being operative to reverse bias the collector-base juncition of said protection transistor and to provide reverse biasing of the base-emitter junction of said protection transistor in the absence of said transients so as to render said protection transistor normally conductive, the level of said reference bias voltage being such that the base-emitter junction of said protection transistor is forward biased in response to transients exceeding a threshold level below said given level to permit conduction in the emitter-collector path of said protection transistor to divert transient currents away from said semiconductor device;
• and wherein
• said emitter of said protection transistor is connected to said semiconductor device with substantially zero offset voltage between said circuit point and said semiconductor device.

In a television receiver including an image reproducing kinescope;

• a source of operating supply voltage including high voltage for said kinescope;
• a video signal processing circuit comprising a semiconductor device including a semiconductor junction coupled to a circuit point at which high voltage transients caused by kinescope arcing may appear, said semiconductor junction being susceptible of damage from electrical stress when said transients exceed a given level;
• a protection circuit arrangement comprising:
• a protection transistor with a collector electrode coupled to an operating potential, a base electrode, and an emitter electrode connected to said circuit point;
• and
• means for applying a reference bias voltage to said base electrode in such manner that the bias of said base electrode is determinable independent of bias of said semiconductor device and bias at said circuit point, said reference bias boltage being operative to reverse bias the collector-base junction of said protection transistor and to provide reverse biasing of the base-emitter junction of said protection transistor in the absence of said transients so as to render said protection transistor normally nonconductive, the level of said reference bias voltage being such that the base-emitter junction of said protection transistor is forward biased in response to transients exceeding a threshold level below said given level to permit conduction in the emitter-collector path of said protection transistor to divert transient currents away from said semiconductor device.