Patent GB-1046754-A (GB)
Title: Improvements in or relating to self-generating invertors including controllable semiconductor rectifiers
IPC: H03L5/00
Filed: 1964-09-21
Abstract: 1,046,754. Semi-conductor rectifier inverter oscillator circuits. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. Sept. 21, 1964 [Sept. 24, 1963], No. 38385/64. Addition to 978,787. Heading H3T. [Also in Division H2] The operating frequency of, and thus the output voltage of an S.C.R. type self-oscillating inverter supplying, for example, fluorescent lamps is controlled by a parallel tuned circuit including a temperature dependent resistor which increases the damping on the circuit as the current increases and so increases the frequency. Controlled rectifiers 1, 1<SP>1</SP> are connected in push-pull to an output transformer 3 tuned by a capacitor 6 such that the reactance of the output circuit is capacitive. This reactance series resonates with the windings of transformer 7, the secondaries 9, 9<SP>1</SP> of which are connected to rectifier circuits 14, 14<SP>1</SP>, 15, 15<SP>1</SP> to provide in operation a reverse bias for the gate electrodes. Connected across the output circuit, through an inductor 21, is a parallel tuned circuit 19, 20, arranged such that each time the circulating current passes beyond zero it changes the saturation state of the core 24 of a feedback transformer producing pulses in secondary windings 25, 25<SP>1</SP>. The pulse in one winding renders conducting the non-conductive SCR and this renders the other non-conductive. In this way the inverter self-oscillates. The output feeds a number of lamps 12 connected in series with respective inductors 11 so that if one lamp is not required it may be shortcircuited without unduly changing the frequency of operation. During the starting-up period of the circuit the load may be small and changing as the lamps ignite. To maintain the output more constant the frequency determining tuned circuit 20, 19 includes a positive temperature coefficient resistor such as a lamp 22 which, when the circuit is first switched on, has a lowresistance value causing the circuit to be lightly damped and the frequency to be low. This causes a fall in the output voltage of the inverter. The lamp is heated by the circulating current allowing the output to rise. Further, a series of reversely connected pairs of Zener diodes or an alternative non-linear resistor is connected across the lamp so that if the circulating current rises above a safe value the Zener diodes greatly increase the damping, lowering the frequency and so reducing the output voltage. Zener diodes alternatively or in addition could be connected across the impedance 21 if it is replaced by a capacitor. Starting may be ensured by connecting a capacitor across one of the SCR's to provide an initial current flow through the output circuit. 1,046,758. Transistor switching circuits. CSEPELI SZERSZAMGEPGYAR. July 21, 1965, No. 31132/65. Heading H3T. [Also in Division H2] The initial energization of the coil of an electromagnet or relay is accelerated by applying a high voltage to the coil through a capacitor and the de-energization is accelerated by discharging the capacitor through the coil. In Fig. 1a the electromagnet or relay coil L 1  is initially energized by rendering Tr 1  conducting so that charging current flows from a high voltage source UT 2 , maintenance of the desired current being effected by the flow of current from a lower voltage source UT 1 . To de-energize the coil, Tr 1  is rendered non-conducting and Tr 3  conducting with the result that the capacitor C e  is now connected reversely across the coil so as rapidly to de-energize it. A diode D 1  provides a discharge current path for L 1  should Tr 1  and Tr 3  both be non-conducting, while diode D 2  prevents the higher voltage source discharging into the lower voltage source. Transistor Tr 1  may be replaced by simultaneously operated separate transistors for the two voltage sources. By exchanging the positions of Tr 3  and C e  the upper point of the coil L 1  may be grounded with the negative supply voltage terminals.