Patent GB-909969-A (GB)
IPC: H02M7/5383
Abstract: 909,969. Transistor inverter-oscillator circuits. PHILIPS ELECTRICAL INDUSTRIES Ltd. July 23, 1959 [July 26, 1958; Feb. 17, 1959; July 3, 1959], No. 25320/59. Class 40 (6). [Also in Group XXXV] An inverter comprises two push-pull connected alternately conducting transistors having connected between the collector electrodes a tapped inductor and a capacitor for causing the frequency of operation of the inverter to be of the same order as the cut-off frequency of the transistors, the collector electrodes being crosscoupled to the base circuits and the bases by a circuit including resistance and capacitance such that a reverse pulse is applied to the bases prior to reversal of the alternating collector voltage so as to remove charge carriers from the base zones. Fig. 3 shows a self-oscillating inverter circuit comprising two alternately conducting transistors 1, 2 having a frequency determining tuned output circuit 319 and operating at a frequency close to the cut-off frequency of the transistor. The collector and base circuits are cross-coupled through resistance capacitor networks 21, 23 and 22, 24, the impedance of the capacitors at the operating frequency being considerably less than that of the resistors, whereby the trailing edge of the current pulse applied to the base leads the corresponding collector current pulse and whereby a reverse pulse is provided at the base to remove charge carriers from the base zone before the alternating collector potential reverses. The time constant of the resistance capacitor networks is greater than a period of the output wave so that a bias is developed across the networks which prevent the flow of base current until the next reversal of the alternating collector electrode potential takes place. The tuning capacitor 19 could alternatively be connected across a larger transformer winding 3 and the collector electrode or electrodes connected to tappings on the inductor (Fig. 5, not shown), or the resistors could be connected to a tertiary winding instead of to the collectors as illustrated in an alternative circuit (Fig. 1, not shown) producing a squarewave output and not in accordance with the invention. In Fig. 6, the feedback is provided by a transformer winding 4 and a single resistance-capacitance network 8, 25 is used in the base circuits to provide the desired shaping of the base current wave forms. In this embodiment, one of the secondary windings 12 is tuned instead of the primary winding and this winding feeds one of the heaters of a luminescent tube and also feeds the discharge path of the tube through a variable inductor 16. The second winding 11 feeds the second heater and also the. starting electrode 15. A similar discharge tube could be connected to the windings of the transformer shown in Fig. 3. Alternatively, the circuit could feed an electro-luminescent panel, the panel itself providing the tuning capacitor 19. The no-load output voltage of the inverter may be arranged to be many times more than the discharge voltage of the tube so as to ensure starting of the tube, improve the efficiency of operation and increase the light output at lower supply voltages. In a further alternative arrangement (Fig. 8), feedback windings 4, 4<SP>1</SP> feed the resistors 23 and 24 and the capacitors 21 and 22 are connected between taps on the collector winding or (as in Fig. 7, not shown) directly to the collectors. The capacitors in Fig. 8 are shunted by series tuned circuits 26, 27 which shape the feedback current wave to provide a sharp cut-off and a reverse current pulse. These series tuned circuits may alternatively be connected between a collector and the base of the second transistor (Fig. 9, not shown) so that a narrower base current wave is produced together with the reverse current pulse. The separate tuned circuits could alternatively be replaced by a single tuned circuit connected between the bases (Fig. 10, not shown). It is suggested that where the leakage inductance of the transformer is sufficient the choke 16 of Fig. 6 could be omitted.