1,214,817. Electroluminescence. GENERAL ELECTRIC CO. 14 Dec., 1967 [6 Feb., 1967 (2)], No. 56931/67. Heading C4S. [Also in Divisions G1, H2 and H3] A silicon controlled rectifier is triggered by light from an injection luminescent junction device transmitted to a light sensitive junction of the rectifier by a fibre optic element. The light-emitting diode (or L.E.D.) may have a hemispherical surface (Fig. 1b, not shown) secured to an optic fibre bundle by clamping means (22) having the same index of refraction as the fibres. In Fig. 1 light emitting diodes 17, 18 may simultaneously cause light sensitive thyristors or triacs to conduct energy to the load during one half cycle under the control of a variable pulsing network 16. If one L.E.D. is reversed full wave control is obtained. Variation of the power and the load may be effected by varying the phase or frequency of the control pulses. Fig. 2 shows a circuit operable as an inverter or as a reversing switch controlled by switches 41 and 42. A capacitor 37 charges until L.E.D. 32 conducts and emits light to trigger thyristors 25, 28. Capacitor 37 is discharged by the diode and the thyristors are switched off by a comutating circuit C.C. Subsequently L.E.D. 33 conducts to switch on thyristors 26, 27, the wavelength of the two L.E.D's being different so that the desired thyristors only are switched on. The sequence of switching may alternatively be obtained by a phase-shift network (Fig. 3, not shown) or the L.E.D. may be such as to emit light of different wavelengths for forward and reverse bias so as to trigger the corresponding thyristors (Fig. 4, not shown) to provide the control sequence or reversing of the switch. The different wavelengths may be obtained, in a further alternative, by selectively operable light filters. If the D.C. power supply is replaced by an A.C. supply or relatively high frequency the circuit could be operated as a cycle-converter. In Fig. 5 (not shown) the lower arms of the bridge of Fig. 2 are replaced by diodes and a single L.E.D. (47) is phase controlled through a triac the L.E.D. emitting light of different wavelengths on the different half cycles to selectively operate the corresponding thyristor for inverter or reversing switch operation. The L.E.D. is also shown controlling thyristors (67SP1/SP, 68SP1/SP) in a transformer type four way rectifying system or reversing switch.
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