Patent GB-1026173-A (GB)
Title: Electronic switching circuits
IPC: G01R33/24
Filed: 1962-10-15
Abstract: 1,026,173. Semi-conductor switching circuits; bi-stable and monostable circuits. VARIAN ASSOCIATES. Oct. 15, 1962 [Oct. 25, 1961], No. 39001/62. Heading H3T. A switching circuit for supplying current from a source 23 to a load 21 comprises two four-layer diodes 41, 43 connected in series with the source and the load, and a resistor 49 connected in parallel with the series combination of one four-layer diode 43 and the. load 21, the resistance of the resistor being greater than that of the diodes when conducting but considerably smaller than that of the diodes when not conducting. Thus, when the switch is " open " leakage current through diode 41 flows mainly through resistor 49 and leakage-current flow through the load 21 is reduced to a negligible value. In the circuit of Fig. 3 the "open" state of the switch is achieved, on first switching on, by applying a negative pulse or edge to the capacitor 51, which switches the further four-layer diode 44 on. A voltage substantially equal to the supply voltage is thus established across capacitor 52. Then when a positive edge is applied through capacitor 51 to switch diode 44 off, the cathode of diode 41 is sent negative so that approximately twice the supply voltage is established across diode 41, this being sufficient to switch diode 41 on. Conduction in diode 41 permits a voltage approximately equal to the supply voltage to be established across four-layer diode 43, this being sufficient to permit the diode to conduct. To switch the circuit off, a negative pulse to the cathode of diode 44 switches that diode on once more, the resultant positive pulse through capacitor 52 switching diode 41 and thus diode 43 off. Zener diode 54 and resistor 53 damp out overswings in the voltage established across the load 21 which in the embodiments described is inductive, being the signal head for a nuclearprecession magnetometer. Fig. 4 shows a monostable circuit which when switched on restores itself to the original condition after a predetermined delay. In this circuit the diode 44 is supplied from a separate power supply 55 rather than from source 23. Diode 44 is first made to conduct by the application of a negative pulse through the capacitor 51. The subsequent application of a positive pulse switching diode 44 off causes the cathode of diode 41 to go negative by approximately the voltage of source 55, thus switching diode 41 on, diode 43 thereafter also switching on. Capacitor 56 now charges through diode 41 and variable resistor 58 until a sufficient voltage is reached to cause diode 44 to conduct, the resultant positive pulse at the cathode of diode 41 switching this diode off and thereafter diode 43. The circuit then remains in this state until the next application of a positive pulse via capacitor 51. In a second monostable circuit, Fig. 5, diode 44 conducts in the quiescent state as before. While diode 44 conducts, capacitor 61 charges so that when diode 44 is switched off and diodes 41 and 43 are switched on by the application of a positive pulse via the capacitor 51, the emitter of transitor 64 moves negatively with respect to its base so that the transistor conducts. The potential difference across diode 44 is then insufficient to make the diode conduct. However, as capacitor 61 discharges, the potential at the junction of resistors 68, 69 rises, so eventually reversebiasing diode 70 as the voltage established by Zener diode 66 is exceeded. When the voltage has risen sufficiently diode 44 switches on, and the quiescent condition is restored.