Half current switch with feedback

Details Half current switch with feedback Half current switch with feedback

1988-02-17

1989-02-21

Shoop, Jr., William M.

Electrical transmission or interconnection systems

Switching systems

Condition responsive

307254, 307448, 307246, 307454, 307443, H03K 1908

Patent

active

048067857

ABSTRACT:
A half current switch comprising: at least one input transistor, a load resistance connected between a first voltage reference and the collector of the input transistor, a constant-current resistance connected between the emitter of the input transistor and a second voltage reference, and a feedback means including at least one feedback connected to the constant-current resistance. The feedback means further includes means for biasing the feedback transistor to drive a current through the constant current resistance which, when flowing, increases with an increasing main current and decreases with a decreasing main current through the input transistor. The feedback means thus causes a constant current to be drawn by the input transistor when it is conducting, thereby controlling the capacitance of the input transistor while maintaining the output level constant.
In a preferred embodiment, the feedback means comprises a PNP transistor with its base connected to the collector of the input transistor, with its emitter connected to the first voltage reference, and with its collector connected to the emitter of the input transistor. The PNP transistor not only acts as a feedback device to control current, but also acts to prevent oscillations when a speed-up capacitor is used in the circuit.

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patent: 4641046 (1987-02-01), Becker et al.
patent: 4701642 (1987-10-01), Pricer
patent: 4725743 (1988-02-01), Anderson

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