PT74682B - ELECTRONIC STARTER FOR FLUORESCENT TUBE HAVING COOPERATING TIMER CIRCUIT WITH OVERVOLTAGE CIRCUIT AND PREHEATING CIRCUIT - Google Patents

Abstract

1. An electronic starter for a fluorescent lamp powered by an a.c. source and consisting of : a. a preheating circuit comprising a series arrangement of at least : (1) the lamp filament ; (2) a switching element activated by means of a gate electrode ; b. a time-delay circuit comprising a series arrangement of at least : (3) a set of resistors constituting a bridge, for the control of the said gate electrode ; c. an overvoltage circuit comprising a series arrangement of at least : (4) an overvoltage capacitor, (5) an inductive element ; characterized in that : d. the switching element is unidirectional and in that the preheating circuit also comprises a series arrangement of : (6) a diode whose conductivity direction is the same as that of the switching element and which is intended to limit the operation of the preheating circuit to the positive half cycles of the supply voltage which correspond to the conduction of said diode, by means of the voltage charge of at least one capacitance in series with a resistor connected to the gate of the switching element ; e. the time-delay circuit also comprises a time-delay capacitor arranged in series with the supply source during the negative half cycles and in parallel with at least a fraction of the resistor bridge for applying a voltage to the gate, which voltage is increasingly negative during the periods when the switching element is non-conducting and thus progressively delays the closure of the switching element during each positive half cycle ; f. the overvoltage circuit is arranged in parallel with the switching element in order that as from the start of the positive half cycles the overvoltage capacitor is charged during the periods having an increasing delay time at the closure of the switching element, after which, at the closure of this element it is discharged across the switching element in the inductive element, which inductive element is the primary winding of an auto-transformer arranged in series in the pre-heating circuit.