Current switch with bipolar switching transistor and .beta. comp

Details Current switch with bipolar switching transistor and .beta. comp Current switch with bipolar switching transistor and .beta. comp

1993-03-31

1994-09-13

Stephan, Steven L.

Electricity: power supply or regulation systems

Self-regulating

Using a three or more terminal semiconductive device as the...

323312, 3072966, G05F 316

Patent

active

053472101

ABSTRACT:
A current switch (30) includes a switching transistor (Q1) having a collector electrode for coupling to a first voltage source (Vcc), an emitter electrode, and a base electrode for receiving a control signal (V.sub.IN1). Switching transistor (Q1) is responsive to the control signal (V.sub.IN1) to turn on to produce a collector current (I.sub.CQ1). A bias circuit (26) is coupled to the emitter electrode of the switching transistor (Q1) for causing the collector current (I.sub.CQ1) of the switching transistor (Q1) to have a predetermined value. The bias circuit includes first and second transistors (Q3 and Q4) having base electrodes coupled in common. The first transistor (Q3) has a collector electrode coupled to the emitter electrode of the switching transistor (Q1) and an emitter electrode for coupling to a second voltage source (Vss). The second transistor has a collector electrode for coupling to a current source (24) and an emitter electrode for coupling to the second voltage source (Vss). A third transistor (Q6) has a collector electrode coupled to the emitter electrode of the switching transistor (Q1), a emitter electrode coupled to the base electrode of the first transistor (Q3), and a control electrode coupled to the collector electrode of the second transistor (Q4). The third transistor (Q6) reduces the dependance of the collector current (I.sub.CQ1) on the .beta. of the switching transistor (Q1) to make the collector current (I.sub.CQ1) less sensitive to process variations.

REFERENCES:
patent: 4528496 (1985-07-01), Naokawa et al.
patent: 4730124 (1988-03-01), Metz
patent: 4879505 (1989-11-01), Barrow et al.

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