Patent GB-977153-A (GB)
Title: Improvements in or relating to automatic circuit breakers
Inventor: JACKETS ALBERT EDMUND
IPC: H02H3/087
Filed: 1961-03-20
Abstract: 977,153. Semi-conductor switching circuits. GENERAL ELECTRIC CO. Ltd. March 12, 1962 [March 20, 1961], No. 10054/61. Heading H3T. [Also in Division H2] An overload protective arrangement includes a semi-conductor controlled rectifier 14 connected in series between supply terminals 1, 2 and output terminals 12, 13, switch means 32 operable to cause a current pulse to be applied to the gate of the rectifier 14 to fire the rectifier and a switching circuit to render the rectifier quiescent in response to the initiation of overload conditions. In Fig. 1 on the closure of a retractive (" start " switch 32, current flowing through an initially discharged capacitor 18 and a Zener diode 37 applies a pulse to the gate of the rectifier 14 to fire it so that the protected load 39 is energized. To interrupt the supply, a retractive " stop " switch 33 is closed to apply a pulse to the gate of a further semi-conductor controlled rectifier 20. The rectifier 20 fires and current flows through the primary coil 16 of a transformer 11 and the capacitor 18 with the result that the voltage induced in the secondary coil 17 of the transformer drives the anode of the rectifier 14 negative and renders the rectifier 14 quiescent. When the capacitor 18 has become fully charged the rectifier 20 becomes quiescent. Should, however, the current in the load become excessive, the voltage drop across a series resistor 10 becomes sufficient to render a transistor 21 conducting and the resulting current through the primary winding 23 of a transformer 24 causes a current pulse to be applied from secondary winding 29 to the gate of the rectifier 20. The rectifier 20 fires and with result that the rectifier 14 becomes quiescent as described above. The Zener diode 37 prevents the rectifier 14 being fired by operation of the switch 32 until the capacitor 18 has become discharged through a resistor 19 and so enabled the rectifier 20 to be fired again should the overload condition persist. Fig. 2 shows a modified arrangement in which the capacitor 68 is normally charged by a battery 66 through a high resistor 67. In this case the rectifier 52 is fired by current flowing from the capacitor 68 through Zener diodes 74, 75 and transformer 73 when the " start" switch 69 is operated. To switch off the supply to the load 78, a " stop " switch 70 is operated to fire the further rectifier 63. The capacitor 68 is then connected across the rectifier 52 and renders it quiescent. The capacitor 68 becomes completely discharged and is then charged in the opposite sense by current from the main supply battery 42 through the load 78 and the rectifier 63. When the capacitor is fully charged in the opposite sense, the rectifier 63 becomes quiescent and the current through the load 78 is interrupted. The capacitor 68 then discharges and is recharged by the battery 66, so that the correct voltage across the Zener diodes 74, 75 for re-firing the rectifier 52 only appears when the arrangement has been restored to its initial condition. Specification 976,862 is referred to.