GB840907A - Improvements in or relating to quick-acting cut-out devices - Google Patents

Abstract

840,907. Protective cut-out arrangements. SOC. DE CONSTRUCTION D'APPAREILS BARDON. March 13, 1958 [April 26, 1957], No. 8091/58. Class 38 (5). [Also in Group XL (c)] A solenoid R3 is energized to trip open contacts C when the current I in a D.C. circuit exceeds a predetermined value and causes a transistor N1 to become conductive. In Fig. 3 a rectifier G is protected by the tripping of the contacts C in the A.C. supply to the rectifier when the voltage produced by the D.C. load current across a shunt R1 exceeds a value determined by an opposing bias derived from a transformer T, rectifiers E1 and a resistor R2, the base of the transistor N1 being biased by the difference between these voltages. In Fig. 4 the bias normally applied to the base of a transistor N2 is such that this transistor conducts and causes the potential at a terminal 5 of a resistor R4 to bias the transistor N1 to its non-conducting state. When the current through the shunt R1 exceeds a predetermined value, the voltage drop across the shunt tends to make the base b 2 of transistor N2 positive with respect to the emitter e 2 and the resulting reduction in the emitter-collector current reduces the potential at terminal 5. This renders the base b 1 of transistor N1 negative with respect to the emitter e 1 so that current starts to flow in the emitter-collector circuit and the resulting change in potential at a terminal 8 of the resistor R7 makes the base b 2 of the transistor N2 more positive, so that an abrupt change to the state in which the transistor N2 is non-conducting and the transistor N1 is conducting occurs and the solenoid R3 is fully energized to trip open the contacts C.