CONTROL CIRCUIT FOR GENERATING A STEP-TYPE CONTROL SIGNAL AND A CONTINUOUSLY VARYING CONTROL SIGNAL WHOSE AMPLITUDE CHARACTERISTIC REPEATS AT THE STEP TRANSITION

摘要

CONTROL CIRCUIT FOR GENERATING A STEP-TYPE CONTROL SIGNALAND A CONTINUOUSLY VARYING CONTROL SIGNAL WHOSE AMPLITUDECHARACTERISTIC REPEATS AT THE STEP TRANSITIONABSTRACT OF THE DISCLOSUREA control circuit for use with an adjustable resistanceto generate a first control signal whose amplitude is a functionof the setting of the resistance, and which varies substantiallycontinuously as the resistance varies, and to generate a secondcontrol signal which appears as step-like signal whose levelis changed over from a first level to a second level at a predeter-mined setting of the resistance. A pair of transistors is providedwith their emitter electrodes connected in common to a referencepotential and with the variable resistance coupled to the collectorelectrode of one transistor. The adjustable output tap from whichthe first control signal is derived is connected to the base elec-trode of the one transistor. An impedance is coupled to thecollector circuit of the one transistor, and a current source isconnected in common to the variable resistance and to the impedancesuch that the variable resistance and impedance are coupled betweenthe collector circuit and the current source. An output of theimpedance is connected to the base electrode of the other transistor,and the second control signal is derived from the collector electrodeof the other transistor, whereby as the setting of the adjustableoutput tap changes, the voltage applied to the base electrode ofthe one transistor, as well as the first control signal, correspond-ingly changes from a first amplitude toward a second amplitude untilthe predetermined setting is reached, whereupon the relative conduc-tivities of the transistors is reversed and the first control signalchanges back to the first amplitude. Thus, if the setting of theadjustable resistance increases from, for example, an initialsetting, the first control signal correspondingly increases froma first amplitude. When the predetermined setting is reached,the second control signal undergoes a step-wise transition, andthe first control signal returns to its initial amplitude whichis further increased with additional increases in the setting ofthe adjustable resistance.This control circuit advantageously can be used toselectively control either of two devices, wherein one deviceis controlled as a function of the first control signal when thesecond control signal is at one level, and the other device iscontrolled as a function of the first control signal when thesecond control signal is at its other level. The control circuitalso can be used to control the operation of a device over firstand second operational ranges, the first range being selectedwhen the second control signal is at its first level, and thesecond range being selected when the second control signal is atits second level.