GB1308284A - Self-biased class c oscillators - Google Patents

Abstract

1308284 Supply systems for consuming devices THORN ELECTRICAL INDUSTRIES Ltd 25 Jan 1972 [25 Jan 1971] 3102/71 Heading H2H [Also in Division H3] A class-C oscillator driving a fluorescent tube 60 produces half-sinusoid collector current pulses in a transistor 11 whose two main path electrodes 12, 15 are connected to respective supply terminals, one connection being through a parallel tuned circuit 13 and also a series tuned circuit, the parallel tuned circuit having a lower frequency than the series one, and including an inductor 203 which is coupled to a feedback winding 18 connected between the base 17 and a bias capacitor 25, whose value is N1/N2.I B /I C .C; where C is the parallel lined circuit capacitance 22a, N1 and N2 are the numbers of turns on the said inductor and feedback windings 20a, 18, and I B and I C are the peak base and collector currents. The ratio I C /I B is between 3 and 10. The series tuned circuit is formed by an inductor 21, which could be the leakage inductance of the transformer 23 whose primary constitutes the parallel tuned circuit inductance 20a, and a capacitance formed by the effective capacitance presented by the parallel circuit between the collector and the point of connection of the inductor 21. For a parallel tuned frequency (output frequency) of 20 KHZ, a series tuned frequency of 30 KHZ is selected to give the best compromise between peak transistor current and optimum current pulse shape, the latter also being controllable (44b, 44d, 44f, Fig. 3, not shown) by selection of resistors 27, 31. Diodes 30, 32 protect the transistor, and a diode 28 discharges the negative voltage built up on C25 during each cycle. Transients are suppressed by L63, C64, C65, R66, and the ferrite cored transformer 23 drives the fluorescent tube 60, or an electroluminescent panel (68, Fig. 6, not shown), in the latter case a PNP transistor being used. An inductor (67, Fig. 6, not shown) in the base circuit produces a reverse bias at the base to compensate for storage time (t s , Fig. 4, not shown) in the transistor. A push-pull circuit (Fig. 7, not shown) employs two transistors whose collectors are connected to opposite ends of the transformer 23 primary (20b, 20c), and circuitry basically similar to Fig. 5.