Amplifiers – Having light-controlled or activated device
Patent
1990-10-09
1992-02-18
Mottola, Steven
Amplifiers
Having light-controlled or activated device
330308, 250214A, 359189, H03F 308
Patent
active
050897888
ABSTRACT:
Where a high bias voltage is required for a photo-element of a photo-receiver, a high voltage is applied to an amplifier which amplifies a photo-current created by the photo-element, when a power supply is turned on. In a prior art photo-receiver, the amplifier may be broken due to this high voltage. In the present invention, the photo-receiver is provided with a protection circuit comprising a diode connected between a power supply circuit and a photo-element, a resistor connected in parallel with the diode, and a first capacitor having one end thereof connected to an anode of the diode and the other end thereof connected to a reference potential. Constants of the circuit components are set such that a time constant of the supply of the power to the amplifier is smaller than a rising time constant of the supply of the power to the photo-element and larger than a falling time constant of the supply of the power to the photo-element. Accordingly, the supply of the power to the photo-element is started after the potential at the input terminal of the amplifier has been established and the potential at the input terminal of the amplifier floats after the supply of the power to the photo-element has been fully extinguished. As a result, the amplifier does not suffer breakdown at the time of power-on and a surge voltage is not applied to the input terminal of the amplifier at the time of power-off.
REFERENCES:
patent: 4188551 (1980-02-01), Iwasaki et al.
patent: 4620321 (1986-10-01), Chown
Mottola Steven
Sumitomo Electric Industries Ltd.
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