GB1175895A - Improvements in or relating to Voltage Controlled Negative Resistance Circuits - Google Patents

Abstract

1,175,895. Protective arrangements. R. A. GIBLIN. 7 May, 1968 [8 March, 1967], No. 10788/67. Heading H2K. [Also in Division H3] For use as a self-actuating protective switch responsive to an excessive value of V, the negative resistance region of the circuit of Fig. 5 is made as nearly as possible parallel to the current axis by reducing R2, the switch being self-resetting upon reduction of the voltage V. In a current limiting circuit, two circuits as in Fig. 5, one having a negative resistance approaching infinity, are connected in parallel across the voltage V (giving characteristic of Fig. 7, not shown); and two such pairs may themselves be arranged in parallel with reverse biased protective diodes between them (to give the characteristic of Fig. 8, not shown). The voltage controlled negative resistance circuit, Fig. 5, has a transistor T1 across the control voltage V, a second transistor T2 in the emitter base circuit of Tl and deriving its own base current from the voltage V through a variable resistance R2 which controls the value of the negative resistance (R, Fig. 1, not shown), and a third transistor T3, connected in series with T2 and in the base-collector circuit of T1. Transistor T3 has in its base circuit an e.m.f. source and a variable resistance R3 which controls the current peak (Ip) of the voltage-current characteristic, and may also have a collector resistor to control the slope of the initial positive resistance part of the characteristic. Instead of the transistor T3, there may be a F.E.T. or a M.O.S.T. with its gate open-circuited, or a drift or diffusion transistor with its base open-circuited, the current peak (Ip) then being fixed. In a further modification, the transistor T3 together with its base resistor R3 and e.m.f. source, may be replaced by a second complete circuit as in Fig. 5 (i.e. Fig. 11, connected in Fig. 10, at XX, not shown). The circuit thus acts like a tunnel diode.