GB899354A - Improvements in or relating to time-lag electric relay devices employing transistors - Google Patents

Abstract

899,354. Protective cut-out arrangements. REYROLLE & CO. Ltd., A. Sept. 26, 1958 [Sept. 27, 1957], No. 30356/57. Class 38 (5). [Also in Group XL (c)] A time delay protective relay circuit comprises a capacitor arranged to be charged through the collector impedance of a transistor and connected through a rectifier to a transistor amplifier having a contact making relay in its output circuit, the arrangement being such that the capacitor charges until the voltage across its electrodes is sufficient to cause the rectifier to conduct and so apply a voltage to the transistor amplifier to cause the relay to operate. In Fig; 6, when the current through a conductor N rises above a predetermined value, the output voltage from a transformer N2, N3 is such that a relay N1 operates. Contact K3 accordingly changes over and connects a capacitor D in series with the collector electrode of a constant current charging transistor circuit A so that the capacitor commences to charge linearly. When the voltage across the capacitor exceeds the bias on rectifier D1, the rectifier conducts and applies a voltage to the input electrode of a transistor amplifier E, F causing the first transistor E to be cut off and the second F to become conducting so that a relay H is operated. Positive feedback may be applied between the collector of transistor F and the base of transistor E to improve the switching as, for example, in Fig. 4 (not shown). The charging time of the capacitor and thus the delay in operating the relay may be varied by varying a resistor in the emitter circuit of the charging transistor A and by varying the initial voltage across the capacitor D. This latter variation is effected by a potentiometer L connected to the capacitor when the relay contact K3 is in its normal position. The circuit is such that the delay varies inversely with the excess current in the conductor N since the output from the transformer N2, N3 is rectified and is used as the source of charging current supplied by transistor A. The characteristic may be changed from an inverse time-voltage characteristic to an inverse time-voltage-squared characteristic by inserting a shaping network O in series with the emitter current path. Such a shaping circuit may comprise a series of biased diodes (Fig. 8, not shown) or a series of non- linear resistors (Fig. 9, not shown). Alternatively, a characteristic in which the slope progressively increases instead of decreases may be obtained by means of a different arrangement of diodes (Fig. 10, not shown). When the delay is to be independent of the voltage, the current in the emitter circuit of transistor A may be derived from a battery of constant voltage or from a diode voltage stabilizing circuit. In an alternative embodiment (Fig. 7, not shown), the relay N1 and its contact K3 is replaced by a trigger circuit comprising two transistors cross-coupled, the base of the first transistor being fed from the output of the network O and the collector of the second transistor being connected to two diodes performing the function of contact K3. In a further embodiment (Fig. 4, not shown), the change-over contact K3 is replaced by a single contact which opens when operation is initiated, the capacitor being connected permanently in series with the charging transistor A. In Figs. 2 and 3 (not shown), the operation of the circuit is initiated by contacts in the base circuit of the charging transistor instead of in the collector circuit.