Control circuit for generating a step-type control signal and a

Abstract

A control circuit uses an adjustable resistance to generate a first control signal whose amplitude varies with the setting of the resistance and a second, step-like control signal whose level changes from a first to a second level at a predetermined setting of the resistance. The variable resistance is coupled to the collector of one of a pair of transistors whose emitters are commonly connected to a reference potential. The adjustable resistance's tap, which provides the first control signal, is connected to the base of the one transistor. A collector impedance and the variable resistance are coupled between the collector circuit of the one transistor and a voltage source. An output of the impedance is connected to the base of the other transistor, whose collector provides the second control signal. As the setting of the adjustable tap increases, the first control signal and the voltage at the base of the one transistor correspondingly increase from a first toward a second amplitude until the predetermined setting is reached. Then the relative conductivities of the transistors are reversed, and the first control signal reverts to its first amplitude, while the second control signal undergoes a step-like transition. Additional increases in the setting of the adjustable resistance again raise the first control signal from its first amplitude.