Photocoupler apparatus capable of shortening switching time of o

Details Photocoupler apparatus capable of shortening switching time of o Photocoupler apparatus capable of shortening switching time of o

1990-05-16

1991-05-07

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Signal isolator

307311, G02B 2700

Patent

active

050139266

ABSTRACT:
A photocoupler apparatus comprises an output MOSFET, a series circuit of a first photoelectromotive force diode array and a diode and connected to the gate and substrate of the MOSFET, a series circuit of a second photoelectromotive force diode array and a resistor and connected between both ends of the diode, and a normally-ON drive transistor. The diode is connected in a forward bias direction to the direction of a light current generated by the first diode array. When a charge current to be supplied to the MOSFET is large, most of the light current flows through the forward-biased diode to the output MOSFET and is not influenced by the current limitation by the resistor. When the charge current decreases, the diode is reverse-biased and the gate-substrate voltage of the MOSFET is higher than a voltage generated across the first diode array. The transistor is driven by a voltage produced across the resistor and is kept at a state between ON and OFF, thus preventing charges accumulated between the gate and substrate of the MOSFET from being discharged. When then first and second diode arrays stop generating photoelectromotive force, the charges accumulated between the gate and substrate of the MOSFET are discharged through the resistor.

REFERENCES:
patent: 4227098 (1980-10-01), Brown et al.
patent: 4390790 (1983-06-01), Rodriguez
patent: 4655316 (1987-05-01), Hodges
patent: 4931656 (1990-06-01), Ehalt et al.
patent: 4939375 (1990-07-01), Walters et al.

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