GB1024542A - An over and under voltage protection device using semi-conductors - Google Patents

Abstract

1,024,542. Protective arrangements. HOUCHIN Ltd. Sept. 4, 1962 [Sept. 4, 1961], No. 31713/61. Heading H2K. [Also in Division H3] An under-voltage and over-voltage protective arrangement comprises a transistor CT having its emitter-base circuit connected to a potential dividing arrangement providing two non-linear paths of different resistance and effective at different voltage values to cause the transistor to change its state. As shown, one higher resistance path includes one or two Zener diodes 4, 5 connected between a tapping 6 on a potential divider 1 and the transistor base and a resistor 7. A lower resistance path includes two or three Zener diodes 10 ... 12 connected between a tapping 9 on the divider 1 and the transistor emitter and a resistor 8. The transistor is' non- conducting until the voltage applied to terminals 2, 3 reaches a lower value at which the diodes 4, 5 become conducting with the diodes 10 ... 12 remaining non-conducting. The resulting voltage drop across the resistor 7 biases the transistor CT into conduction and a relay RR in the collector-emitter circuit is operated. The transistor remains conducting until the voltage at the terminals 2, 3 reaches a higher value at which the diodes 10 ... 12 become conducting. The resulting voltages across the resistors 7, 8 are now such that the transistor is cut off and the relay RR is released. When the voltage at the terminals falls to an intermediate value the voltages across the resistors 7, 8 become such that the transistor again conducts. The complete drawing shows the use of the above arrangement, in conjunction with a frequency sensitive arrangement to protect a three-phase supply system.