Patent GB-935235-A (GB)
Title: Improvements in or relating to self-generating inverters having controlled semi-conductor rectifiers
IPC: H05B41/282
Filed: 1962-01-19
Abstract: 935,235. Inverting; supply systems for fluorescent lamps. PHILIPS ELECTRICAL INDUSTRIES Ltd. Jan. 19, 1962 [Jan. 23, 1961], No. 2051/62. Classes 38 (2) and 38 (4). [Also in Group XL (c)] In a self-generating inverter comprising one or more controlled semi-conductor rectifiers, the rectifiers are rendered periodically conducting and non-conducting under the control of a reverse current pulse produced in the control electrode circuit of one of the rectifiers in the non-conducting state, said reverse current pulse providing a forward current pulse in the circuit of the control electrode of the same rectifier or a following one in order to render it conducting again. In the embodiment of Fig. 1, a pair of silicon-controlled rectifiers are connected with push-pull inputs to a parallel circuit comprising capacitor 6 and primary winding 4 of output transformer 5, a centre tap of the primary winding being connected to the D.C. supply through inductor 14. The control electrodes of the two receifiers 1, 2 are connected to the negative supply through windings 15, 16 respectively wound on an annular ferrite core 17, such that if a current pulse is passed through a winding 18 on the core a forward current pulse passes to rectifier 1 and a reverse current pulse to the control electrode of rectifier 2 with the result that rectifier 1 conducts and rectifier 2 remains non-conducting. The current flowing through the rectifier 1, the upper half of the winding 4 and inductor 14 impulses the oscillatory circuit 4-6 causing the latter to ring, and a series circuit is completed through rectifier 1 and the D.C. supply which series circuit includes the inductor 14 and that part of the impedance of circuit 4-6 effective between the centre tapping of the winding 4 and the anode electrode of rectifier 1, the series resonance frequency of this circuit being chosen that the current through rectifier 1 is pulsatory and has a pulse duration equal to or less than half a cycle of the generated alternating voltage. When the pulsatory current passes through zero rectifier 1 is rendered non-conducting and a very short reverse current pulse flows through its control electrode circuit and winding 15, resulting in a forward current pulse being produced in winding 16 passing through the control electrode circuit of rectifier 2 and causing it to conduct whereby the cyclic operation is repeated. The core 17 may be saturated by the starting pulse 18 so that it can be brought into opposite saturation condition by the following reverse current pulse. An A.C. or switching pulses of alternating polarity may be supplied to the winding 18 as a result of which the rectifiers 1, 2 would be rendered conducting in turn. In a second embodiment, Fig. 3 (not shown), a single controlled rectifier has its main current path connected through an oscillatory circuit and an inductor to a D.C. supply and its control electrode circuit connected to a delay line having its other end short circuited. The reverse current pulse in the control electrode circuit when the rectifier is cut off is reflected by the short circuit of the delay line with reversed polarity to the control electrode of the rectifier so that it is rendered conducting again by this forward current pulse. In a third embodiment, Fig. 4, three controlled rectifiers 1, 1<SP>1</SP>, 1<SP>11</SP> are arranged in a ring with the control electrode of each rectifier connected to a circuit including the primary winding 21 of a first coupling transformer and a secondary 22 of a second coupling transformer, winding 22 being shunted by a diode 23 which passes reverse current pulses through the corresponding control electrode circuit and the secondary winding 24 of the first coupling transformer being shunted by a diode 28 which is cut off with respect to the reverse current pulses. Winding 24 is connected through autotransformer 26 to delay line 19, which delays the reverse pulses with a time interval of one third of the cycle of oscillation and is terminated by the primary winding of the second coupling transformer of rectifier 1<SP>1</SP> such that a forward current pulse is passed to the control electrode of this circuit. The control electrode circuit of rectifier 1<SP>1</SP> is similarly coupled to rectifier 1<SP>11</SP> and so on, so that each rectifier conducts for one-third of the cycle of operation. The load circuit fed by the self-generating oscillator may be a combination of fluorescent lamps 10-13 provided with capacitors 9 or inductors 8 acting as power factor correction impedances. Specification 226,216 is referred to.