Patent GB-978787-A (GB)
Title: Improvements in or relating to self-generating controlled semi-conductor inverters
IPC: H02M7/516
Filed: 1962-02-09
Abstract: 978,787. Semi-conductor inverting circuits. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. Feb. 9, 1962 [Feb. 13, 1961], No. 5070/62. Heading H3T. [Also in Division H2] In a self-generating invertor including at least one controlled semi-conductor rectifier, one main current circuit electrode of the or each rectifier being connected to one terminal of a D.C. supply through a series resonant circuit of which the capacitive part is coupled with a load circuit, the rectifier or rectifiers are periodically rendered conducting by a pulse produced under the control of the current passing through a subcritically damped second resonant circuit connected across the capacitive part of the first resonant circuit. The second resonant circuit includes at least one resistive component and one non-linear element which changes from one saturation state to its other saturation state just after the zero passage of current through or of the voltage across one of the reactive elements of the second resonant circuit so as to produce the pulse which renders the rectifier conducting. As shown in Fig. 1, the emitters of two silicon controlled rectifiers 1, 2 are connected to one terminal of a D.C. supply 3 and the collectors to the other terminal through a series resonance circuit comprising capacitor 4, centre tapped primary winding 5 of output transformer 7 and inductor 6. When the invertor is connected across the supply 3 a current pulse is produced across resonant circuit 4, 5, 6 by capacitive network 26, 27 such that one of the rectifiers, e.g. 2, becomes conducting for a time determined by the natural frequency of the resonant circuit 4, 5, 6. The current passing through the main current circuit of the rectifier and this resonant circuit passes through zero after one half period of the series resonance frequency with the result that rectifier 2 is cut off. The voltage across capacitor 4 produces through resistor 15 and inductor 20 a voltage drop across the parallel combination of inductor 13 and capacitor 14 which circuit elements together with primary winding 16 on a saturable core 17 form a subcritically damped resonant circuit across capacitor 4. The voltage drop across inductor 13 and capacitor 14 results in a current flowing through capacitor 14 and the primary winding 16 which leads in phase with respect to the voltage across capacitor 4. Thus after each zero passage of the current through capacitor 14 and winding 16 the core 17 abruptly changes over from one magnetic saturation state to the opposite one so that a current pulse is produced in the appropriate secondary winding 18, 19. If initially rectifier 2 is conducting then the diode 22 is opened and the current pulse will flow through winding 18 and this diode towards resistor 24 and the parallel emitter controlelectrode of rectifier 1 causing this rectifier to commence conducting. On the next passage through zero of the current through winding 16 a current pulse will pass through winding 19 and diode 23 to rectifier 2 so that this rectifier again conducts and rectifier 1 will be switched off. The switching frequency of the invertor is determined by the values of the reactive and resistive elements 13 to 16 and 20, 21 of the second resonant circuit and is independent of the voltage of source 3 and the load connected to winding 8. The load circuit may consist of the parallel combination of four fluorescent gas discharge lamps 9, 9<SP>1</SP>, 10 and 101 each connected in series with a control impedance 11, 11<SP>1</SP> and 12, 12<SP>1</SP> respectively. Specifications 226,216, 935,235 and 940,669 are referred to.