JP2014053771A - Semiconductor relay device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a readily inexpensive and compact semiconductor relay device.SOLUTION: A charge/discharge control circuit 10 is disposed in parallel with a photodiode array 2 to control an electrical charge/discharge of a gate of an output MOSFET 3. The charge/discharge control circuit 10 has a FET 11 having a drain and source connected to a gate and source of the output MOSFET 3, respectively, and a gate connected to one end of the photodiode array 2. An impedance element disposed between the gate and source of the FET 11 does not include any resistor but includes a diode 12 having an anode and a cathode connected to the gate of the FET 11 and the source of the FET 11, respectively.

Description

  The present invention relates to a semiconductor relay device including a photodiode array that receives an optical signal and generates a photovoltaic force.

  2. Description of the Related Art Conventionally, there is a semiconductor relay device that uses a photodiode array that receives an optical signal and generates a photovoltaic force as a photoelectric conversion device for operation. The photodiode array is formed by connecting a plurality of photodiodes in series. In this semiconductor relay device, the photodiode array has an anode and a cathode connected to the gate and source of the output FET. A depletion mode FET for charge / discharge control is provided between the gate and source of the output FET, and the gate and source of this FET is a resistor for generating a bias voltage provided in series with the photodiode array. Connected to both ends. (For example, FIG. 5 of patent document 1).

Japanese Patent Laying-Open No. 2003-46116 (FIG. 5)

  In recent years, semiconductor relay devices are required to be reduced in cost and size. For this purpose, for example, a method of downsizing the photodiode array can be considered. However, the conventional semiconductor relay device is configured such that when the photodiode array generates photovoltaic power, the voltage generated across the resistor is higher than the threshold voltage of the charge / discharge control FET. There is a need. For this reason, when the photodiode array is reduced in size, the generated photocurrent is reduced accordingly, so that it is necessary to increase the resistance. An increase in resistance leads to an increase in cost, which is not preferable. Conversely, if the resistance is reduced, it is necessary to increase the size of the photodiode array so that the generated photocurrent increases.

  In view of such a problem, an object of the present invention is to provide a semiconductor relay device that can be easily reduced in cost and reduced in size.

  A semiconductor relay device according to one embodiment of the present invention includes a photodiode array in which photodiodes are connected in series, and a photovoltage of the photodiode array is applied between a gate and a source, and the drain and the source are controlled on and off. An output MOSFET, and a charge / discharge control circuit that controls charge / discharge of charges to and from the gate of the output MOSFET, the charge / discharge control circuit comprising: an impedance element provided in series with the photodiode array; A drain and a source are connected to a gate and a source of the output MOSFET, respectively, and the gate includes an FET connected between the impedance element and the photodiode array, and the impedance element includes a resistor. And the anode is connected to the gate of the FET. Sword is connected to the source of the FET, comprising one or a plurality of serially connected, a diode.

  The diode preferably has a breakdown voltage higher than the threshold voltage of the FET.

  The diode is preferably a Zener diode.

  In addition, the impedance element is provided in parallel with the diode, and has one or a plurality of series-connected first electrodes having an anode connected to a source of the FET and a cathode connected to a gate of the FET. Preferably two diodes are included.

  A semiconductor relay device according to another aspect of the present invention includes a photodiode array in which photodiodes are connected in series, and a photovoltage of the photodiode array is applied between a gate and a source, and on / off control is performed between the drain and the source. An output MOSFET, and a charge / discharge control circuit for controlling charge / discharge of charges to and from the gate of the output MOSFET, the charge / discharge control circuit comprising an impedance element provided in series with the photodiode array; , A drain and a source are connected to a gate and a source of the output MOSFET, respectively, and a gate is connected between the impedance element and the photodiode array, and the impedance element includes a resistor. Does not contain and the anode is connected to the source of the FET One or a plurality of diodes connected in series with the cathode connected to the gate of the FET, and the diode; the drain and the gate are connected to the source of the FET; And a second FET connected to the gate of the FET.

  The second FET preferably has a threshold voltage higher than the threshold voltage of the FET.

  According to the present invention, since the impedance element provided between the gate and source of the charge / discharge control FET does not include a resistor, it is easy to reduce the size of the semiconductor relay device.

1 is a circuit diagram illustrating a configuration of a semiconductor relay device according to a first embodiment. FIG. 6 is a circuit diagram illustrating a configuration of a semiconductor relay device according to a second embodiment. FIG. 6 is a circuit diagram illustrating a configuration of a semiconductor relay device according to a third embodiment.

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

(Embodiment 1)
FIG. 1 is a circuit diagram showing a configuration of a semiconductor relay device according to the first embodiment. The semiconductor relay device of FIG. 1 is light-coupled to a light-emitting element 1 configured by an LED element that outputs an optical signal in response to an input signal, and the light-emitting element 1, and receives an optical signal output from the light-emitting element 1. A photodiode array 2 that generates photovoltaic power, an output MOSFET 3, and a charge / discharge control circuit 10 that controls charging / discharging of the gate charge of the output MOSFET 3.

  The photodiode array 2 has a plurality of photodiodes connected in series. The charge / discharge control circuit 10 includes a depletion type MOSFET 11 for charge / discharge control, and a Zener diode 12 as an impedance element provided between the gate and source of the MOSFET 11. MOSFET 11 has a drain and a source connected to the gate and source of output MOSFET 3, respectively, and the gate is connected between Zener diode 12 and photodiode array 2. The Zener diode 12 has an anode connected to the gate of the MOSFET 11 and a cathode connected to the source of the MOSFET 11. The Zener diode 12 has a breakdown voltage higher than the threshold voltage of the MOSFET 11, and has a role of charging the gate-source capacitance of the output MOSFET 3 by the breakdown current when the breakdown occurs. .

  The anode of the photodiode array 2 is connected to the gate of the output MOSFET 3 and the drain of the MOSFET 11. The cathode of the photodiode array 2 is connected to the gate of the MOSFET 11 and the anode of the Zener diode 12. The source of the MOSFET 11 is connected to the cathode of the Zener diode 12 and the source of the output MOSFET 3. The drain and source of the output MOSFET 3 are output terminals 4a and 4b of the semiconductor relay device, respectively. With such a configuration, the photovoltage of the photodiode array 2 is applied between the gate and source of the output MOSFET 3, and the drain and source of the output MOSFET 3 are on / off controlled. As a result, the output terminals 4a and 4b can be electrically connected or opened.

  The operation of the semiconductor relay device of FIG. 1 will be described.

  When an input signal is applied to the light emitting element 1, the light emitting element 1 emits light, and the photodiode array 2 receives this optical signal and generates photovoltaic power. At this time, in the charge / discharge control circuit 10, the drain and source of the MOSFET 11 are in a conductive state, and therefore, a potential difference is generated between both ends of the Zener diode 12. However, when this potential difference is lower than the breakdown voltage of the Zener diode 12, no current flows through the Zener diode 12. When the potential difference generated at both ends of the Zener diode 12 becomes larger than the threshold voltage of the MOSFET 11, the drain and source of the MOSFET 11 become nonconductive.

  When the drain and source of the MOSFET 11 become non-conductive and the Zener diode 12 breaks down, the voltage generated at both ends of the photodiode array 2 is applied to the gate of the output MOSFET 3 and the gate and source of the output MOSFET 3 Charges are charged in between. Eventually, when the gate-source potential exceeds the threshold value of the output MOSFET 3, the drain-source of the output MOSFET 3, that is, the output terminals 4a and 4b become conductive.

  When the input signal is no longer applied to the light emitting element 1, the light emitting element 1 stops emitting light and no photoelectromotive force is generated in the photodiode array 2. Then, in the charge / discharge control circuit 10, there is no potential difference between both ends of the Zener diode 12, that is, the gate and source of the MOSFET 11, and the drain and source of the MOSFET 11 shift from the non-conductive state to the conductive state. Then, the charge charged between the gate and source of the output MOSFET 3 is discharged through the MOSFET 11, so that the potential between the gate and source of the output MOSFET 3 becomes lower than the threshold value, and the drain and source of the output MOSFET 3 are drained. That is, the output terminals 4a and 4b are opened.

  In the configuration of FIG. 1, the impedance element for controlling the on / off state of the MOSFET 11 does not include a resistor and is configured by a Zener diode 12. Since the diode can generally be formed with an area smaller than the resistance, the configuration of FIG. 1 facilitates miniaturization of the semiconductor relay device.

  When the impedance element is constituted by a resistor as in the prior art, the voltage generated at both ends of the resistor when the photodiode array 2 generates photovoltaic power is higher than the threshold voltage of the MOSFET 11. Thus, it is necessary to configure a semiconductor relay device. For this reason, in order to reduce the cost of the semiconductor relay device, for example, when the photodiode array 2 is reduced in size, the generated photocurrent is reduced, so that it is necessary to increase the size of the resistor. On the other hand, when the resistor is downsized, it is necessary to enlarge the photodiode array 2 so that the generated photocurrent increases.

  On the other hand, in the configuration of FIG. 1, the Zener diode 12 is used as the impedance element, so that the semiconductor relay device can be easily downsized. In FIG. 1, one Zener diode 12 is used, but a plurality of Zener diodes 12 may be connected in series. In this case, the number of Zener diodes 12 may be determined based on the breakdown voltage and the threshold voltage of MOSFET 11.

  Here, the Zener diode 12 having a stable breakdown voltage is used as the diode constituting the impedance element. However, the present invention is not limited to this, and other types of diodes may be used. However, the use of a Zener diode with a stable breakdown voltage enables more stable operation.

(Embodiment 2)
FIG. 2 is a circuit diagram showing a configuration of the semiconductor relay device according to the second embodiment. The basic configuration of the semiconductor relay device of FIG. 2 is substantially the same as that of FIG. However, in the charge / discharge control circuit 10A, the configuration of the impedance element provided between the gate and the source of the MOSFET 11 is different from that in FIG. That is, as an impedance element, a Zener diode 13 and a plurality of second diodes 14 connected in series are provided in parallel and in opposite directions. The Zener diode 13 has an anode connected to the gate of the MOSFET 11 and a cathode connected to the source of the MOSFET 11. The zener diode 13 has a breakdown voltage higher than the threshold voltage of the MOSFET 11 as in the zener diode 12 of FIG. 1, and when the breakdown occurs, the gate of the output MOSFET 3 is generated by the breakdown current. -Has the role of charging the capacity between sources. On the other hand, the second diode 14 has an anode connected to the source of the MOSFET 11 and a cathode connected to the gate of the MOSFET 11.

  The operation of the semiconductor relay device of FIG. 2 will be described.

  When an input signal is applied to the light emitting element 1, the light emitting element 1 emits light, and the photodiode array 2 receives this optical signal and generates photovoltaic power. The generated photocurrent flows to the second diode 14 through the MOSFET 11 which is in a conductive state. At this time, no current flows through the Zener diode 13. When the voltage generated across the second diode 14 exceeds the threshold voltage of the MOSFET 11, the drain and source of the MOSFET 11 become non-conductive.

  When the drain and source of the MOSFET 11 are in a non-conductive state, electric charge is efficiently charged between the gate and source of the output MOSFET 3. At this time, if the Zener diode 13 is broken down, the charging efficiency is further improved. Eventually, when the gate-source potential exceeds the threshold value of the output MOSFET 3, the drain-source of the output MOSFET 3, that is, the output terminals 4a and 4b become conductive.

  When the input signal is no longer applied to the light emitting element 1, the light emitting element 1 stops emitting light and no photoelectromotive force is generated in the photodiode array 2. Then, in the charge / discharge control circuit 10, there is no potential difference between both ends of the second diode 14, that is, the gate and source of the MOSFET 11, and the drain and source of the MOSFET 11 shift from the non-conductive state to the conductive state. Then, the charge charged between the gate and source of the output MOSFET 3 is discharged through the MOSFET 11, so that the potential between the gate and source of the output MOSFET 3 becomes lower than the threshold value, and the drain and source of the output MOSFET 3 are drained. That is, the output terminals 4a and 4b are opened.

  In the configuration of FIG. 2, the impedance element for controlling the on / off state of the MOSFET 11 does not include a resistor, and includes a Zener diode 13 and a second diode 14. Therefore, it becomes easy to reduce the size of the semiconductor relay device. In addition, since the second diode 14 is provided in parallel with the Zener diode 13, the charging path for the gate-source capacitance of the output MOSFET 3 is increased as compared with the first embodiment. The response time can be increased.

  Here, the Zener diode 13 having a stable breakdown voltage is used as the diode constituting the impedance element. However, the present invention is not limited to this, and other types of diodes may be used. However, the use of a Zener diode with a stable breakdown voltage enables more stable operation.

(Embodiment 3)
FIG. 3 is a circuit diagram showing a configuration of the semiconductor relay device according to the third embodiment. The basic configuration of the semiconductor relay device of FIG. 3 is substantially the same as that of FIG. However, in the charge / discharge control circuit 10B, the configuration of the impedance element provided between the gate and the source of the MOSFET 11 is different from that in FIG. That is, as the impedance element, a plurality of diodes 15 connected in series and the second FET 16 are provided in parallel. The diode 15 has an anode connected to the source of the MOSFET 11 and a cathode connected to the gate of the MOSFET 11. In the second FET 16, the drain and the gate are short-circuited and connected to the source of the MOSFET 11, and the source is connected to the gate of the MOSFET 11. The second FET 16 has a threshold voltage higher than the threshold voltage of the MOSFET 11 and, when conducting, plays a role of charging the gate-source capacitance of the output MOSFET 3 with its drain current. have.

  Since the drain and the gate of the second FET 16 are short-circuited, the drain-source is brought into conduction only when the voltage between the drain and the source exceeds the threshold voltage. For this reason, the second FET 16 performs substantially the same operation as the Zener diode 13 of FIG. 2, and the operation of the circuit of FIG. 3 is substantially the same as that of FIG. Here, the overlapping operation description is omitted.

  In the configuration of FIG. 3, the impedance element for controlling the on / off state of the MOSFET 11 does not include a resistor, and is configured by the diode 15 and the second FET 16. Therefore, it becomes easy to reduce the size of the semiconductor relay device. Moreover, since there are a plurality of charging paths for the gate-source capacitance of the output MOSFET 3, the time required for charging is shortened, and the response time can be increased.

  In each of the above-described embodiments, the depletion type MOSFET 11 is provided as the charge / discharge control FET. However, the present invention is not limited to this, and for example, a junction type FET (JFET) may be used. .

  In each of the above-described embodiments, the configuration in which one output MOSFET 3 is provided is shown. However, two output MOSFETs 3 may be connected in parallel.

  The present invention is effective in reducing the cost and size of a device using a semiconductor relay device.

2 Photodiode array 3 Output MOSFET
10, 10A, 10B Charge / Discharge Control Circuit 11 Depletion Type MOSFET (FET)
12, 13 Zener diode (diode)
14 Second diode 15 Diode 16 Second FET

Claims (6)

A photodiode array in which photodiodes are connected in series;
An output MOSFET in which the photovoltage of the photodiode array is applied between the gate and the source and the drain and the source are controlled to be turned on and off;
A charge / discharge control circuit for controlling charge / discharge of charge to and from the gate of the output MOSFET,
The charge / discharge control circuit includes:
An impedance element provided in series with the photodiode array;
A drain and a source connected to a gate and a source of the output MOSFET, respectively, and a gate connected between the impedance element and the photodiode array;
The impedance element does not include a resistor, and
A semiconductor relay device including one or a plurality of diodes connected in series, each having an anode connected to a gate of the FET and a cathode connected to a source of the FET. The semiconductor relay device according to claim 1,
The semiconductor relay device, wherein the diode has a breakdown voltage higher than a threshold voltage of the FET. The semiconductor relay device according to claim 1,
The semiconductor relay device, wherein the diode is a Zener diode. The semiconductor relay device according to claim 1,
The impedance element is
One or a plurality of second diodes connected in series, provided in parallel with the diode, having an anode connected to the source of the FET and a cathode connected to the gate of the FET. A semiconductor relay device. A photodiode array in which photodiodes are connected in series;
An output MOSFET in which the photovoltage of the photodiode array is applied between the gate and the source and the drain and the source are controlled to be turned on and off;
A charge / discharge control circuit for controlling charge / discharge of charge to and from the gate of the output MOSFET,
The charge / discharge control circuit includes:
An impedance element provided in series with the photodiode array;
A drain and a source connected to a gate and a source of the output MOSFET, respectively, and a gate connected between the impedance element and the photodiode array;
The impedance element does not include a resistor, and
One or a plurality of diodes connected in series with an anode connected to the source of the FET and a cathode connected to the gate of the FET;
A semiconductor relay device comprising: a second FET provided in parallel with the diode, having a drain and a gate connected to the source of the FET, and a source connected to the gate of the FET. The semiconductor relay device according to claim 5,
The semiconductor relay device, wherein the second FET has a threshold voltage higher than that of the FET.

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