Patent GB-1321111-A (GB)
Title: Solid-state relay
IPC: H03K17/56
Filed: 1970-05-29
Abstract: 1321111 Transistor relay circuits NORTH AMERICAN PHILIPS CORP 29 May 1970 [2 June 1969 29 April 1970] 26121/70 Heading H3T A solid state relay comprises (A) a pulse generating circuit energizable by an actuating signal and having a capacitor shunted by a negative resistance device and chargeable via at least one field effect transistor arranged as a constant current device, and (B) a circuit having terminals for connection to a load and a source of power and having controllable solid state means switchable from a high impedance state to a low impedance state by the pulses generated in (A). Oscillators.-As shown in Fig. 1, an A.C. or D.C. actuating signal is applied to a rectifier bridge 16 comprising two Zener and two ordinary diodes, connected to charge a capacitor 26 via field effect transistors 23, 24 acting as a constant current source until discharged by a breakdown device 27 which may be a unilateral four-layer diode, an avalanche transistor, a double base diode or a tunnel diode. This produces pulses in a transformer primary 28. In Fig. 2 (not shown) A.C. input is applied via a constant current device to the capacitor which is discharged through the transformer primary at a greater frequency than the supply by a bilateral breakdown diode, thus producing trains of pulses of alternate polarity.  Coupling.-As shown in Fig. 1, the oscillator is coupled to operate the switching section by a transformer 29, but in Fig. 7 (not shown) the breakdown device in the oscillator is light emissive and co-operates with a photo-field effect transistor in the switching section. A similar arrangement is used in Fig. 8 (not shown) but in this case it is the capacitor in the oscillator which is light emissive. In Fig. 9 (not shown) the oscillator breakdown device is in series with a piezo-electric crystal, cemented to a similar crystal in the switching section. Switching section.-As shown in Fig. 1, this comprises back-to-back thyristors 33, 34 triggered by pulses induced in transformer secondaries 31, 32 to switch an A.C. load on terminals 36, 37. Fig. 2 (not shown) is similar but the triggering pulses change polarity, so are connected to the gates via a pair of diodes. In Fig. 3 (not shown) two S.C. circuits are switched by triacs, and in Fig. 4 (not shown) a single A.C. or D.C. circuit is switched by a bilateral transistor controlled by pulses from a single secondary winding applied to its base via a diode. In Fig. 5 (not shown) A.C. or D.C. is switched by a back-to-back pair of junction transistors, controlled by separate secondary windings, with a protective diode in series with each collector. In Fig. 6, an A.C. supply 84 is switched either to a load 86 by a "normally closed" triac 76 (oscillator off) or to a load 87 by a "normally open" triac 81. This is triggered on by pulses in transformer secondary 72; another secondary winding turns on a third triac 83 which short circuits the gate of 76 to turn it off. The transformer core is of "square loop" material and has a further winding 73 in series with triac 76, which biases the transformer so that 81 cannot be triggered on until 76 is off (i.e. "break before make").