Patent GB-1053859-A (GB)
IPC: H02M1/40
Filed: 1962-11-09
Abstract: 1,053,859. Inverting. ROTAX Ltd. Nov. 28, 1963 [Nov. 9, 1962], No. 42366/62. Heading H2F. [Also in Divisions G3 and H3] In a parallel inverter which incorporates controlled rectifiers which are controlled by an oscillator means are provided to ensure reliable starting. Main circuit.-Rectifiers 11, 12 are connected to the ends of a primary winding 8 of a transformer whose secondary winding feeds a load 21 through suitable filter circuits. The D.C. input is supplied to the centre tap of the winding 8 through a winding 16 which serves to shape the output signal, and back e.m.f. in this winding is absorbed in a coupled winding 16a in series with a diode 16b. Commutating capacitors 17, 18 are provided, and to shut off a conducting rectifier 11 or 12 a further rectifier 13 is fired which discharges the capacitor 11 or 12 reversely through it. The rectifier 13 is itself shut off by oscillation through the circuit 66, 67. The rectifiers fire in the order 11, 13, 12, 13, 11, and the delay between the firing of 11 or 12 and subsequent firing of 13 determines the output voltage. Firing pulses for the rectifier 13 are derived from a voltage regulator 27 (Fig. 3, not shown) and the aforesaid delay is dependent on the charging of a capacitor 41. This charging is dependent on feedback through a transformer 42 so that automatic regulation is produced. Control signals to the gates of the rectifiers 11, 12 are derived from a square wave oscillator 22 (Fig. 2, not shown) and applied through lines 23, 24 and diodes 59, 61. Voltage regulator (Fig. 3).-Shut off pulses on line 28 arise when a unijunction transistor 35 is made conductive by the charge on a capacitor 36 reaching a predetermined value. A signal on line 25 derived from the oscillator 22 when either rectifier 11 or 12 is fired momentarily renders a transistor 37 conductive to discharge capacitor 36. This capacitor then charges through a transistor 38 which follows a transistor 39 whose conduction depends on the voltage across capacitor 41. Starting circuit.-Starting may be erratic because time is needed for the oscillator to build up to its normal amplitude. In consequence additional outputs from the oscillator on lines 43, 44 are returned to the line 6 through a series circuit of a diode 45, or 46, a resistor 47, a first normally-closed relay contact 48 and a capacitor 49. In its energized position 50 the relay contact short circuits the capacitor 49. A point intermediate the resistor 47 and contact 48 is connected through a Zener diode to the base of a transistor 52 which controls a further transistor 54 which is connected in series with the relay coil 57 across the D.C. supply. A second normally-closed relay contact 64 in series with a diode 62 or 63 series to short circuit the gate cathode circuits of rectifiers 11, 12. In operation the inverter does not operate until the oscillator amplitude is sufficient to charge the capacitor 49 to a voltage to break down the Zener diode 51, whereupon the relay coil 57 is energized opening contact 64 so that signals can pass to the gates of rectifiers 11, 12. Since the capacitor 49 is discharged through contact 50 on energization of relay coil 57, if the D.C. input falls the inverter will stop until capacitor 49 is recharged. On starting up the inverter would tend to operate at full power saturating the transformer core. To prevent this the capacitor 41 is charged up through a normally closed contact 41 which does not open until the coil 37 is energized.