Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1979-03-19
1981-01-27
Brigance, Gerald L.
Communications: electrical
Condition responsive indicating system
Specific condition
340662, 324126, G08B 2100
Patent
active
042478499
ABSTRACT:
A current limiting voltage sensing circuit especially suited as an annunciator input circuit is disclosed. It includes a radiation emitting device circuit, a current limiting circuit for maintaining the current supplied to the voltage sensing circuit at a substantially constant value while supplying the needed current to the radiation emitting device circuit, and a radiation sensitive device circuit coupled to the radiation emitting device and electrically isolated from it for converting from the radiation signal into an electrical signal. In one arrangement, the input to the voltage sensing circuit is a full-wave rectifier so that it can be used for detecting an ac voltage or a dc voltage in either direction. One arrangement of the current limiting circuit includes a field effect transistor with the drain-to-source forming a variable resistance current path for maintaining the current supplied to the voltage sensing circuit at a substantially constant value, and a circuit connecting the source of the field effect transistor in a feedback relationship to the gate. In one arrangement, the feedback circuit is a resistor in series with the radiation emitting device which is a light emitting diode. The radiation sensitive device in such an arrangement is a photodiode or phototransistor which forms an optical coupler with the light emitting diode.
REFERENCES:
patent: 3665442 (1972-05-01), Brooks
patent: 3991367 (1976-11-01), Chapman et al.
patent: 4025850 (1977-05-01), Spiteri
Alford John H.
Morris Phillip D.
Beta Products, Inc.
Brigance Gerald L.
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