JPH07193220A - Photo thyristor - Google Patents

Abstract

PURPOSE:To provide a very reliable photo thyristor which can be reduced in size and is resistant to pulse noise. CONSTITUTION:In one and the same substrate wherein a photo thyristor 16 is formed, a normally-on type MOSFET 17 which is to be connected between the gate and the cathode of the photo thyristor 16 is formed and a photo transistor 18 to be connected to the gate of the normally-type MOSFET 17 is also formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high noise resistant photothyristor in which a photothyristor and a gate control element of the photothyristor are monolithically formed in the same substrate.

[0002]

2. Description of the Related Art Generally, a photothyristor is usually combined with an infrared light emitting diode and built in an optical coupling element called a photothyristor coupler, which is mainly used for switching an AC circuit and firing a high power triac. There is. A photothyristor that is a switching element,
It is important that it is turned on only when the light which is the input is input and is turned off in all cases when the light is not input.

However, when a voltage with a sharp rise is applied to the photothyristor or when a pulse-like high voltage is applied by lightning or the like, the photothyristor may be turned on even when there is no input. In order to avoid such malfunctions, conventionally, in addition to providing a snubber circuit consisting of a varistor, a resistor, and a capacitor in the entire circuit, a capacitor called a gate capacitor is externally attached between the gate and cathode of the photothyristor, and noise is applied to the gate. The photo thyristor was prevented from being erroneously shot.

Further, in a photothyristor with a zero-cross function provided for the purpose of preventing inrush current as shown in FIG. 3, the gate control circuit operates as a gate and a cathode except when the anode-cathode voltage is near 0V. Due to the short-circuiting between them, the structure is stronger against pulse-like noise than that without the zero-cross function. In FIG. 3, 100 is a photothyristor part,
101 is a normally-off type N-channel MOSFET section.

[0005]

By the way, as a method of preventing the false firing of the photothyristor, when a gate capacitor is used as described above, a large capacitance is required, so that it is not possible to build it in the same element. It is difficult and needs to be externally attached, the number of components is increased, and since it is placed between the gate and the cathode, there is a drawback that the switching response to input ON is deteriorated.

[0006] In addition, for those with a built-in zero cross,
The zero-cross function does not operate within the zero-cross voltage which is usually set to about 20 to 50V, and when a steep voltage is applied, the photothyristor turns on before the zero-cross circuit operates. .

Therefore, an object of the present invention is to reduce the size,
It is to provide a highly reliable photothyristor that is strong against pulse noise.

[0008]

In order to achieve the above object, the present invention provides a normally-on type which is connected between a gate and a cathode of the photothyristor in the same substrate on which the photothyristor is formed. A MOSFET is formed, and a phototransistor connected to the gate of the normally-on type MOSFET is formed.

[0009]

The present invention, as described above, is a normally-on type M
The OSFET is connected between the gate and cathode of the photothyristor, and when the phototransistor connected to the gate of the MOSFET does not receive light as an input signal, the gate and cathode of the photothyristor are short-circuited. Pulse-like noise does not enter the gate and cause the photothyristor to be misfired. This structure allows
Erroneous discharge within the zero-cross voltage generated in the conventional zero-cross type photothyristor is eliminated, and external parts such as a gate capacitor are also unnecessary.

Furthermore, this structure can also be used as a zero-cross circuit by setting the threshold voltage of the MOSFET to an arbitrary voltage.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. 1 and 2 are a sectional view and an equivalent circuit of a photothyristor according to this embodiment, respectively.

It should be noted that, in FIG. 1, parts other than the part related to the structure of the present invention, such as an oxide film other than the MOSFET part, are omitted. A method of manufacturing each element is a well-known technique and will be briefly described.

First, a P-type impurity which becomes the anode 2 of the photothyristor is formed on the N ⁻ substrate 1 from the back surface, and a P-type impurity which becomes the gate 4 of the photothyristor, the source 4 of the MOSFET, the drain 5 of the MOSFET and the base 7 of the phototransistor is formed on the surface. Spread more simultaneously.

Next, N-type impurities are diffused from the surface into the cathode 3 of the photothyristor and the emitter 8 of the phototransistor.

Finally, the photo-thyristor portion 16 and the normally-on type MOSFET portion 1 are diffused in the well 6 of the MOSFET by diffusing a P-type impurity having the same low concentration as the channel of the MOS called channel doping.
7, the phototransistor portion 18 is formed. here,
In each of the above-mentioned parts, a normally-on type MOSFET part 17 is connected between the gate and cathode of the photothyristor part 16, and a phototransistor part 18 is connected to the gate of the normally-on type MOSFET.

Then, each element is wired with Al or the like, and an anode electrode is formed on the back surface to complete the photothyristor of this embodiment. The gate electrode 12 of the MOSFET is provided via a gate oxide film 15 provided between the channels.

Next, the operation will be described. The phototriac chip formed by the above process becomes a photothyristor coupler when incorporated in the same package as the infrared light emitting diode. The light of the infrared light emitting diode is simultaneously applied to the photothyristor portion 16 and the phototransistor portion 18 formed on the same chip.

When the input is turned off, since the phototransistor section is not exposed to light, no voltage is applied to the gate of the MOSFET and the normally-on type FET is in the on state. For this reason, since the gate and cathode of the photothyristor are short-circuited, the photothyristor is never turned on even if noise enters between the A and K or the G and K of the photothyristor.

Next, when the input is turned on and the phototransistor portion is irradiated with light, the phototransistor is turned on and a voltage is applied to the gate of the MOSFET 17.

This voltage is a voltage obtained by subtracting the base-emitter forward voltage of the PNP Tr of the photothyristor portion 16 and the voltage drop of the photothyristor portion 18 from the voltage between A and K, and this voltage exceeds the threshold value of the MOSFET. And the MOSFET is turned off and the gate and cathode of the photothyristor are opened, so that the photothyristor irradiated with light is turned on. The threshold voltage of the MOSFET can be controlled by the amount of impurities for channel doping, and by setting the threshold voltage to about 5 V or less, a zero-cross function photothyristor is obtained.

As described above, according to the photothyristor of this embodiment, when the input is turned off, the gate and cathode of the photothyristor are always short-circuited by the MOSFET, so that even if pulsed noise is entered, the erroneous arc is surely caused. It can be prevented. Further, unlike the conventional case, it is not necessary to externally attach a capacitor having a large capacity, so that the size can be reduced. Furthermore, by setting the threshold voltage of the MOSFET to an appropriate value, it can be used as a photothyristor with a zero-cross function.

Although the vertical type photothyristor has been described in the above embodiments, a lateral type photothyristor and a phototriac can also obtain the same effect as a gate control element.

[0023]

As described above, according to the present invention, it is possible to realize a highly reliable photothyristor which can be miniaturized and can surely prevent erroneous firing even when pulsed noise is introduced.

[Brief description of drawings]

FIG. 1 is a sectional view of a photothyristor according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the photothyristor of FIG.

FIG. 3 is a circuit diagram of a photothyristor according to a conventional example.

[Explanation of symbols]

 1 common film 2 common connection pattern 101 LED chip 103 LED driver IC 105 substrate

Claims (1)

[Claims] 1. A normally-on type MOSFET connected between a gate and a cathode of the photothyristor is formed in the same substrate as the substrate on which the photothyristor is formed, and a gate of the normally-on type MOSFET. A photothyristor formed by forming a phototransistor connected to the.