Patent
1990-07-05
1992-08-11
James, Andrew J.
357 13, 357 38, 357 51, H01L 2714, H01L 2990, H01L 2974
Patent
active
051384159
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a photo-semiconductor device with a zero-cross function, in which a photo-trigger thyristor (including a photo-trigger triac, etc.) to be driven by an optical trigger signal, a MOS field effect transistor (hereinafter referred to as MOSFET) for controlling the gate sensitivity of the photo-trigger thyristor and a Zener diode for protecting a gate oxidized film of the MOSFET, are all formed monolithic in the same semiconductor substrate.
BACKGROUND ART
Recently, photo-trigger thyristors having a built-in zero-cross circuit using a MOSFET are widely used as an ON/OFF switching element for AC control for use in an home electric appliance, an electronic copying machine or the like. Such a photo-semiconductor device is disclosed in, for example, Published Unexamined Japanese Patent Application No. 59-151463 and its corresponding U.S. patent application Ser. No. 451,792, and U.S. patent application Ser. No. 555,025.
FIG. 1 is a general equivalent circuit of a photo-trigger thyristor with a zero-cross function. A photo-trigger thyristor 11 is ignited by an optical trigger signal. A resistor 12 is connected between the gate and cathode K of the photo-trigger thyristor 11. A current path between the source and drain of a MOSFET 13 is connected in parallel to the resistor 12, or is connected between the gate and cathode K of the thyristor 11. The MOSFET 13 has its back gate connected to the cathode K. A Zener diode 14 has its anode connected to the cathode K and its cathode connected to the gate of the MOSFET 13. A voltage pickup circuit 15 comprising capacitors C1 and C2 serves to apply to the gate of the MOSFET 13 a gate bias voltage corresponding to a voltage applied between the anode A and cathode K of the thyristor 11, and this function is equivalently represented by the capacitors C1 and C2. The capacitor Cl has its one electrode connected to the anode A of the thyristor 11, and the other electrode connected to one electrode of the capacitor C2 and the gate of the MOSFET 13. The other electrode of the capacitor C2 is connected to the cathode K. The capacitor Cl is the capacitance of a PN junction formed to pick up a voltage between the anode A and cathode K of the thyristor 11. The capacitor C2 is the combined capacitance of the capacitance of the depletion layer of the PN junction of the Zener diode 14 and the gate capacitance of the MOSFET 13, i.e., it equivalently represents a parasitic capacitance.
A gate current generated by an optical trigger signal supplied to the gate of the photo-trigger thyristor 11 has a smaller value as compared with the gate trigger current of an ordinary thyristor, so that the thyristor 11 is required to have a high gate sensitivity. With the photo-trigger thyristor 11 designed to have a high gate sensitivity, however, the dV/dt withstandability decreases. Like this, the gate sensitivity and the dV/dt withstandability have a trade-off relation. Accordingly, the MOSFET 13 for controlling the gate sensitivity is provided to improve the relation between the gate sensitivity and the dV/dt withstandability so as to prevent the dV/dt withstandability even for the thyristor 11 with a high gate sensitivity from decreasing.
The MOSFET 13 is in an OFF state when the gate voltage is less than the threshold voltage Vth of the MOSFET 13, and the photo-trigger thyristor 11 can operate with its original high gate sensitivity, i.e., it can be turned on by a minute current such as an optical trigger signal current. When the gate voltage becomes equal to or greater than the threshold voltage Vth, the MOSFET 13 is turned on and the gate and cathode K of the photo-trigger thyristor 11 are short-circuited. With the MOSFET 13 rendered on, the thyristor 11 produces the same effect as a thyristor with the cathode and emitter short-circuited. This reduces the gate sensitivity of the photo-trigger thyristor 11 s that it will not be turned on by a minute optical trigger signal current, thus improving the dV/dt withstandability. In order to perform the ab
REFERENCES:
patent: 4224634 (1980-09-01), Svedberg
patent: 4295058 (1981-10-01), Lade et al.
patent: 4396932 (1983-08-01), Alonas et al.
patent: 4779126 (1988-10-01), Herman
James Andrew J.
Kabushiki Kaisha Toshiba
Ngo Ngan Van
LandOfFree
Photo-semiconductor device with a zero-cross function does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photo-semiconductor device with a zero-cross function, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photo-semiconductor device with a zero-cross function will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-350504