| 摘要 |
<p>A photocoupler apparatus comprises an output MOSFET (18), a series circuit of a first photoelectromotive force diode array (32) and a diode (34) and connected to the gate and substrate of the MOSFET (18), a series circuit of a second photoelectromotive force diode array (36) and a resistor (38) and connected between both ends of the diode (34), and a normally-ON drive transistor (26). The diode (34) is connected in a forward bias direction to the direction of a light current generated by the first diode array (32). When a charge current to be supplied to the MOSFET (18) is large, most of the light current flows through the forward-biased diode (34) to the output MOSFET (18) and is not influenced by the current limitation by the resistor (38). When the charge current decreases, the diode (34) is reverse-biased and the gate-substrate voltage of the MOSFET (18) is higher than a voltage generated across the first diode array (32). The transistor (26) is driven by a voltage produced across the resistor (34) and is kept at a state between ON and OFF, thus preventing charges accumulated between the gate and substrate of the MOSFET (18) from being discharged. When then first and second diode arrays (32, 36) stop generating photoelectromotive force, the charges accumulated between the gate and substrate of the MOSFET (18) are discharged through the resistor (34).</p> |
