CIRCUIT ARRANGEMENT WHICH CONTROLS SERIES LOGIC CIRCUIT OF CLOCK CONTROL SOURCE

摘要

A circuit arrangement for the control of the series switching element of a clocked power supply unit has a pulse signal (Vt) delivered by a pulse generator. The pulse-interval ratio of the pulse signal can be varied as a function of a regulating signal (Vc) derived from the output side of the power supply unit and delivered by way of an optoisolator (13). The portion of the circuit employed as pulse generator (1) includes an operational amplifier (10) with feedback at both inputs. One feedback branch of the amplifier (10) contains at the amplifier input a capacitance (15) and a variable resistance. The variable resistance is formed by the parallel connection of a phototransistor (132) of an optoisolator (13) and an ohmic resistor (12). Accordingly, it becomes possible to produce a variation of the pulse-interval ratio of the pulse signal (Vt) either solely by modification of the pulse length or solely by modification of the pulse intervals. One input of the operational amplifier (10) may be connected with a start-stop switching stage (3), which also uses an op-amp ( 20). The two operational amplifiers (10, 20), which both are employed as open collector voltage comparators, can also be made as part of an integrated unit.