GB959777A - Improvements in or relating to transistor current switching apparatus - Google Patents

Abstract

959,777. Transistor timing circuits. A. KUCKENS. Aug. 19, 1960 [Sept. 23, 1959], No. 28857/60. Heading H3T. [Also in Division G1] A transistor unit for operating a switching device for a given time comprises a normally charged capacitor which upon closing a switch causes a transistor to be cutoff until the capacitor has discharged, the transistor being coupled to a second transistor which conducts when the first is non-conducting and so operates a switch. In Fig. 5, transistor 17 normally conducts due to the current through resistors 5, 5<SP>1</SP> and 6 and a capacitor 4 is charged through a resistor 7. On making a contact such as 105 the potential at point A is brought to the reference potential and transistor 17 is cut-off so that a relay 3 is operated. The capacitor 4 however discharges through resistors 5, 5<SP>1</SP> and 6 so that after a time delay transistor 17 again becomes conducting and relay 3 released. A contact of relay 3 such as 104 may be connected across terminals A and B so that the timing sequence will occur even if contact 105 is only momentarily made. The relay is also operable by shining a light on a photodiode 103 so as to produce a pulse at terminal A, a condenser 102 preventing slow changes in the lighting from operating the circuit. The circuit may be operated by a sudden decrease in lighting if the photodiode 103 and resistor 101 are interchanged in position. Stabilization of the operation is obtained by maintaining the two transistors at the same temperature as by embedding them in synthetic resin of high heat-conductivity. The points A, B and C may alternatively be connected to a circuit such as is shown in Fig. 6 comprising two photodiodes 103 and 106. These diodes are arranged in a balanced bridge circuit so that variations, such as those due to temperature, are cancelled out. If diode 106 is shaded it may be arranged that the change in voltage across 103 at dusk causes transistor 109 to conduct and produce an output at A. Alternatively, if 103 is shaded the diode 106 may operate the circuit at dawn. Fig. 7 shows a sequence timer in which the momentary operation of a switch causes relay 3 to operate. This steps on a contact 33 so that capacitors 4 commences to charge, the charging current causing transistor 2 to be conducting and causing the relay 3 to be released. When capacitor 4 is charged transistor 2 becomes non-conducting and relay 3 is operated so that the switch 33 steps on one further position. Transistor 2 now remains cut-off until the charge on condenser 4 has returned to its original discharged condition when the transistor again conducts. Thus the relay may be made to operate and release intermittently at predetermined intervals. It is stated that the circuit may be arranged to recycle when the first sequence is complete. In an alternative embodiment (Fig. 4, not shown), the circuit automatically goes through a sequence of cycles on switching on the starting circuit and without the operation of switch F.