JPH04271515A - Solid-state relay - Google Patents

Abstract

PURPOSE:To set an off-time at current switching longer and to prevent noise production by connecting a resistor composed of a polycrystal silicon resistor between the cathode of a thyristor and the anode of a diode constituting a discharge circuit. CONSTITUTION:A 1st resistor 9a consisting of a polycrystalline silicon resistor whose resistance is 2M ohms and which is connected between the cathode of a thyristor 6 and the anode of a diode 5 is provided. When an input current flowing between input terminals 1 and 1a is interrupted, the lighting of a light emitting diode 2 is stopped and the voltage of a photovoltaic element 3 is dropped. Thus, the thyristor 6 is turned on as the discharge operation and the electric charge stored in the gate of an NMOSFET 7 is discharged. In this case, the NMOSFET 7 is turned off at an OFF time of 300musec by delaying the discharge time through the polycrystal silicon resistor whose resistance is 2M ohms. That is, the OFF operation is relaxed, the OFF time is set longer and the influence of noise at current switching is prevented.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention converts an input signal into an optical signal using a light emitting diode, converts the optical signal into an electrical signal using a photovoltaic diode array optically coupled with the light emitting diode, and outputs the electrical signal. It is used in solid-state relays that use optical coupling to drive field-effect transistors and obtain output contact signals.

0002

2. Description of the Related Art FIG. 5 is a circuit diagram showing an example of a conventional solid state relay. The light-emitting diode 2 lights up due to the voltage applied between the input terminals 1-1a, and the emitted light generates an electromotive force in the photovoltaic element 3 to which the photodiode 10 is cascade-connected. Both ends of the thyristor 6 are connected to both ends of the photovoltaic element 3 via diodes 4 and 5, respectively. Furthermore, the N-pole gate 6a of the thyristor 6 is connected to the connection point between the anode of the photovoltaic element 3 and the anode of the diode 4, and the P gate of the thyristor 6 is connected to the connection point between the cathode of the photovoltaic element 3 and the cathode of the diode 5. Pole gate 6b is connected. The thyristor 6 has two anodes and two cathodes each, each of which is an enhancement type NMOSFET.
It is connected to the gate electrode 7a and back gate electrode (source electrode here) 7b of (field effect transistor) 7. As a result, when an electromotive force is generated in the photovoltaic element 3, the NMOSFET 7 is turned on, and the NM
The load between the output terminals 8-8a connected to the drain 7c of the OSFET 7 is closed.

In this conventional solid state relay, when the light emitting diode 2 is lit, the thyristor 6 is in the "off" state, and the resistance value is extremely high, and the electric charge due to the electromotive force generated in the photovoltaic element 3 is transferred to the diode 4. and 5, and is immediately applied to the gate 7a of the output NMOSFET 7.

Next, when the voltage applied between the input terminals 1 and 1a disappears and the light emitting diode 2 turns off, the voltage generated by the photovoltaic element 3 disappears, but the output voltage is generated by the diodes 4 and 5 and the thyristor 6. NM for
The gate voltage of OSFET7 is maintained as it is. In this state, the voltage of the photovoltaic element 3 decreases due to self-discharge. This voltage drop initially causes diodes 4 and 5 to be in the "off" state. Therefore, the impedance of the N-pole gate 6a and the P-pole gate 6b of the thyristor 6 becomes extremely high, and the thyristor is turned on with an extremely small amount of current. When the voltage further decreases, the N-pole gate 6a or the P-pole gate 6b is biased in the forward direction. Since the sensitivity of the gate is extremely high, the thyristor 6 is turned on by a slight self-discharge current of the photovoltaic element 3.

Since the thyristor 6 has a self-holding characteristic,
Once turned on, the potential between the anode and cathode is 1
It remains "on" until the voltage drops to about V. Therefore, the charge accumulated in the gate 7a of the output NMOSFET 7 is quickly discharged through the thyristor 6, and the NMOSFET 7 is quickly discharged.
ET7 is "off".

[0006]

SUMMARY OF THE INVENTION When the conventional solid state relay described above is used as a power switch element in a power supply circuit, it has the disadvantage that noise is generated during power switching when the switch is turned "off."

FIG. 6 is an input signal waveform diagram and an output signal waveform diagram showing the dynamic characteristics of such a conventional solid state relay. The "on" time of a conventional solid-state relay varies in proportion to the input current of the light emitting diode and the photodiode's photosensitive area, but the "off" time depends on the discharge circuit that discharges the charge accumulated at the gate of the NMOSFET. Since the thyristor's "on" state quickly becomes low resistance, it can turn "off" quickly regardless of the input current. Figure 6 shows a 100V load switching at an input current of 10mA, and the “on” time
The operation time is 300 μsec, and the "off" time is 10 μsec, and when used for power switching, the "off" operation is fast and noise is generated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a solid-state relay that eliminates the above-mentioned drawbacks, slows down the "off" operation during current switching, and prevents noise generation.

[0009]

[Means for Solving the Problems] The present invention provides a photovoltaic device composed of a light emitting device and a cascade connection of a photodiode that generates an electromotive force using light from the light emitting device;
a first diode whose anode is connected to the anode of the photovoltaic element; a second diode whose cathode is connected to the cathode of the photovoltaic element; a thyristor having a polar gate and an anode connected to each other and a polar gate and a cathode connected to the cathode and anode of the second diode, respectively; and the photovoltaic element having a gate and a back gate connected to the anode and cathode of the thyristor, respectively. a field-effect transistor that becomes conductive upon receiving a voltage generated by the thyristor at its gate; Features. Further, the present invention may include a second resistor connected between the anode of the photovoltaic element and the anode of the first diode. Further, in the present invention, it is preferable that the first and second resistors are polycrystalline silicon resistors. Further, in the present invention, it is preferable that the first and/or second resistors made of polycrystalline silicon are formed on the photovoltaic element.

0010

[Operation] Since the first resistor is connected between the cathode of the thyristor, which is a discharge circuit, and the anode of the second diode, the rising operation of the thyristor becomes gradual, and as a result, the charge accumulated at the gate of the NMOSFET is reduced. The discharge time becomes longer and the "off" operation becomes more gradual and the "off"
It takes longer.

[0011] Furthermore, by connecting a second resistor between the anode of the photovoltaic element and the anode of the first diode, the current from the photovoltaic element is controlled, and the NMOSFE
The on operation of the T is controlled and the "on" time can be controlled.

That is, by inserting a first resistor or a first and a second resistor, one can control the "off" and "on" times of the switch, in particular increasing the "off" time and reducing noise when switching currents. This makes it possible to prevent the effects of

Furthermore, by using polycrystalline silicon resistors as the first and second resistors and forming them on the photovoltaic element, the solid state relay of the present invention can be realized without increasing the chip area. can.

[0014]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. In the first embodiment, a photovoltaic element 3 is constructed of a light emitting element 2 connected between input terminals 1-1a, and a photodiode 10 which generates an electromotive force by the light from the light emitting element 2. , a first diode 4 whose anode is connected to the anode of the photovoltaic element 3, a second diode 5 whose cathode is connected to the cathode of the photovoltaic element 3, and an anode and a cathode of the diode 4, respectively. A thyristor 6 has an N-pole gate 6a and an anode connected to it, and a P-pole gate 6b and a cathode connected to the cathode and anode of the diode 5, respectively, and a gate 7a and a back gate (source here) to the anode and cathode of the thyristor 6, respectively. 7b
A solid state relay including two NMOSFETs 7 as field-effect transistors, each having a drain 7c connected to each output terminal 8 and 8a, and becoming conductive upon receiving a voltage generated from the photovoltaic element 3 at its gate. In,

The present invention is characterized by a first resistor 9a made of a 2MΩ polycrystalline silicon resistor connected between the cathode of the thyristor 6 and the anode of the diode 5.
Contains.

Next, the operation of the first embodiment will be explained using FIG. FIG. 2 is an input signal waveform diagram and an output signal waveform diagram showing dynamic characteristics in the first embodiment. When input current is passed between input terminals 1 and 1a, light emitting diode 2
emits light, and the photovoltaic element 3 receives this light and generates a voltage. This voltage is an enhancement type NMOSFET.
7 between the gate 7a and the back gate 7b,
300μ between the drain electrodes 7c of NMOSFET 7
The operation is similar to the conventional example shown in FIG. 5, which closes the load between the output terminals 8 and 8a for an "on" time of sec.

Next, when the input current between the input terminals 1-1a is cut off, the light emitting diode 2 stops emitting light, the voltage of the photovoltaic element 3 decreases, and the thyristor 6 is activated as a discharge operation.
becomes “on” and discharges the charge accumulated in the gate of NMOSFET 7. At this time, by passing the 2MΩ polysilicon resistor 9a and delaying the discharge time, N
It becomes possible to operate the MOSFET 7 "off" with an "off" time of 300 μsec.

Furthermore, if the resistor 9a made of a 2MΩ polycrystalline silicon resistor is formed on a semiconductor chip, there is a concern that the chip area will increase; however, since the polycrystalline silicon resistor has the property of transmitting light, , can be formed on the photovoltaic element 3 which is a photodiode array,
It is possible to prevent an increase in chip area.

FIG. 3 shows the circuit shown in FIG. 1 surrounded by dotted lines.
FIG. 2 is a schematic plan view of a chip showing an example in which a photodiode array and a discharge circuit are integrated into one chip. This chip has gate 7a - back gate 7b of NMOSFET 7 for output.
Wiring pads 11, 12 and 13 connected between
Diodes 4 and 5 and a thyristor 6 are arranged as discharge circuits, and a resistor 9a is formed on the photovoltaic element 3.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention. In the first embodiment shown in FIG. 1, a second resistor 9b made of a polycrystalline silicon resistor is connected between the anode of the photovoltaic element 3 and the anode of the diode 4, which is a feature of the present invention. . Here, the resistor 9b is formed on the photovoltaic element 3 similarly to the resistor 9a.

In the second embodiment, by controlling the current generated by the photovoltaic element 3 using the resistor 9b, it is possible to delay the "on" time of the solid state relay.

[0023]

As explained above, the present invention can delay the "off" operation time of the relay by connecting a polycrystalline silicon resistor in series with the thyristor of the discharge circuit, thereby reducing noise caused by power switching. This has the effect of realizing a solid-state relay that can operate slowly and can be applied to devices that are susceptible to the effects of Furthermore, forming a polycrystalline silicon resistor on the photovoltaic element has the effect of preventing an increase in the area of the chip.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram of the input signal waveform and output signal waveform.

FIG. 3 is a schematic plan view showing the main parts of the chip.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a conventional example.

FIG. 6 is an input signal and output signal waveform diagram.

[Explanation of symbols]

1, 1a Input terminal 2 Light emitting diode 3 Photovoltaic element 4, 5 Diode 6 Thyristor 6a N-pole gate 6b P-pole gate 7 NMOSFET 7a Gate electrode 7b Back gate electrode (source electrode) 7c
Drain electrodes 8, 8a Output terminals 9a, 9b Resistor (polycrystalline silicon resistance) 1
0 Photodiode 11, 12, 13 Wiring pad 14 Chip

Claims (4)

[Claims] 1. A photovoltaic device comprising a light emitting device and a photodiode that generates an electromotive force by light emitted from the light emitting device, and a photovoltaic device having an anode connected to the anode of the photovoltaic device. a second diode whose cathode is connected to the cathode of the photovoltaic element; and a N-pole gate and an anode connected to the anode and cathode of the first diode, respectively, and the cathode of the second diode. and a thyristor having a P-pole gate and a cathode connected to its anode, respectively, and an electric field whose gate and back gate are connected to the anode and cathode of the thyristor, respectively, and which becomes conductive when the gate receives the voltage generated from the photovoltaic element. effect type transistor, the solid state relay comprising a first resistor connected between the cathode of the thyristor and the anode of the second diode. 2. The solid state relay according to claim 1, further comprising a second resistor connected between the anode of the photovoltaic element and the anode of the first diode. 3. The solid state relay according to claim 1, wherein the first and second resistors are polycrystalline silicon resistors. 4. The solid state relay according to claim 3, wherein the first and/or second resistors made of polycrystalline silicon are formed on the photovoltaic element.