Mounting in order to apply two variable dc currents, whose sum is constant, at two different resistances, intended in particular to the controllers level pilots for telecommunication systems with a carrier frequency multichannel

摘要

992,663. Selective signalling. TELEFUNKEN PATENTVERWERTUNGS-G.m.b.H. Feb. 21, 1962 [March 10, 1961; Dec. 5, 1961], No. 6725/62. Heading G4H. [Also in Division H4] In an arrangement for regulating the current through a resistor R a in either direction in a stepwise manner, pulses from a lead k are applied to a counter comprising bi-stable circuits B1. . . B7 each comprising two amplifier members such as RS 1 , TS 2 and each of their amplifiers is connected via gates such as D1, 3; Dl, 4; D2, 3; D2, 4 to the succeeding bi-stable circuits. The left-hand amplifiers TS 1 , TS 3 ... are arranged to supply current, via resistors R 1 , R 2 . . . in parallel, to the resistance Ra. This resistance may be the heater for a thermistor in an adjustable cosine equalizer. Since the circuit counts in binary manner the resistances R1, R2... are arranged so that currents are provided through them in ratios 1:2:4... Forward stepping is arranged by applying blocking potential over lead z to block gates such as D1, 4; D1, 3 so that B 2 is changed over via D2, 4: D2, 3 only on TS 2 becoming conducting. In backward stepping, blocking potential is applied to lead w, so that B 2 is only changed over when TS 1 becomes conducting. Means may be provided for inhibiting the supply of pulses when the counter is saturated in either direction. Two resistances such as Ra may be provided one fed from the lefthand transistors and the other from the right hand transistors. With the use of a polarity sensitive device the arrangement may be made to step forwards or backwards according to the polarity of the input pulses. In a modification Fig. 4 (not shown) the bi-stable circuits comprise two transistors having a common emitter resistance the second having a condenser back coupling its collector to the base of the first, which latter is provided with voltage divider arrangement to provide two well-separated threshold potentials for the first transistor according as this transistor is conducting or not.