JP2007135081A - Semiconductor relay device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact semiconductor relay device with high-voltage resistance, and high-heat resistance. <P>SOLUTION: The semiconductor relay device includes an LED 1 which outputs an optical signal in response to an input signal, a photo diode array 2 which receives the optical signal from the LED 1 to generate a prescribed voltage, a charging/discharging circuit 3 which charges/discharges the voltage generated by the photo diode array 2, and a MOSFET 4 for output which is turned on/off by a control voltage from the charging/discharging circuit 3 and is made of silicon carbide. Since an output part is improved in voltage resistance, heat resistance, and efficiency, the compact high-performance semiconductor relay device can be obtained with higher voltage resistance, higher heat resistance, and less loss than conventional semiconductor relay devices using MOSFETs of Si semiconductors. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor relay device that opens and closes based on an optical signal output in response to an input signal, and more particularly to a semiconductor relay device having a MOSFET made of SiC material as an output semiconductor element.

  In recent semiconductor relay devices, characteristics such as high voltage, high temperature operation, and low loss have been demanded in sophisticated automotive equipment and power saving household appliances. The characteristics required for such a semiconductor relay device largely depend on the high breakdown voltage, high temperature, and low loss characteristics of the semiconductor relay device, particularly the output semiconductor element portion.

  Conventionally, as a semiconductor relay device of this type, for example, as disclosed in Patent Document 1, a light emitting element that converts an electric signal into an optical signal by an input signal and a light signal from the light emitting element are received and a predetermined start is made. And a light receiving element that generates electric power, and an output MOSFET is turned on and off based on the electromotive force. This semiconductor relay device has one silicon MOSFET as an output semiconductor. However, with this configuration, it has been difficult to realize a high breakdown voltage relay exceeding 1000 V due to the breakdown voltage characteristics of the MOSFET.

  On the other hand, as a semiconductor relay device for high withstand voltage, for example, as shown in Reference Document 2, two LEDs that emit an optical signal according to an input signal and an electromotive force are generated by receiving the optical signal. Eight photodiode arrays, eight control circuits connected to both ends of the light receiving element, and eight withstand voltage 750 V class double diffusion field effect type transistors (Double-diffused Metal Oxide Semiconductor Fielder) controlled by the control circuit 2. Description of the Related Art A semiconductor relay device is known that includes an effect transistor (hereinafter simply referred to as a DMOSFET) and a protective diode for protecting the gate of each DMOSFET.

  In the semiconductor relay device of this configuration, eight sets of four DMOSFET coupling circuits connected in series are provided using eight MOSFETs, and their sources are connected to each other so that these DMOSFET coupling circuits are in reverse series with each other. The semiconductor relay output is taken out from both drains. A protective diode, a control circuit, and a photodiode array are connected in parallel between the gate and source of each DMOSFET. As described above, the semiconductor relay of Reference Document 2 has a breakdown voltage of 3000 V by connecting four DMOSFETs having a breakdown voltage of 750 V in series.

  However, this semiconductor relay requires four DMOSFETs each in the DMOSFET coupling circuit, and accordingly, each DMOSFET requires a photodiode array, a control circuit, and a protection diode, increasing the number of parts and making the circuit configuration complicated. At the same time, a large amount of mounting space is required, resulting in high costs.

As another conventional example, as shown in Reference 3, it is composed of two LEDs and two dielectric separation chips, and each dielectric separation chip is connected in series to the peripheral portion of the dielectric separated substrate. The four DMOSFETs formed in this manner and the same number of photodiode arrays as the DMOSFETs formed in the central portion of the substrate for receiving the output light of the LED, and the photodiode arrays and the shunt resistors are respectively connected to the source and source of the DMOSFETs. A semiconductor relay connected in parallel between gates is known. In this semiconductor relay, the number of mounting parts is reduced by forming each part on two dielectric isolation chips, but in this case as well, the DMOSFET, the photodiode array connected to each of them, and the shunt resistor are reduced. The number of necessary circuit elements in the chip did not change, and there was a limit in reducing the size of the dielectric isolation chip. In addition, a cooling device such as a heat radiating plate for heat generation needs to be installed as the high voltage circuit with a high withstand voltage is reduced, and there is a problem that the entire relay device is enlarged by this cooling device.
U.S. Pat. No. 4,268,883 JP 2005-65150 A Japanese Patent Laid-Open No. 2005-252909

  The present invention has been made in order to solve the above-described problem. A MOSFET that is an output element of a semiconductor relay uses a MOSFET made of a SiC material instead of a MOSFET made of a Si material that has been used so far. The purpose of the present invention is to provide a semiconductor relay device that can be used at a higher temperature and realizes a high voltage characteristic with a smaller number of output semiconductor elements, and is compact, has a high withstand voltage, and has an extremely excellent high temperature characteristic. .

  In order to achieve the above object, the invention of claim 1 includes a light emitting element that outputs an optical signal in response to an input signal, a photodiode array that receives the optical signal from the light emitting element and generates a predetermined voltage, In a semiconductor relay device comprising a charge / discharge circuit for charging / discharging a voltage generated by the photodiode array, and an output MOSFET controlled by the charge / discharge circuit, and opening / closing the output MOSFET in response to the input signal, The output MOSFET is made of silicon carbide (SiC).

  According to a second aspect of the present invention, in the semiconductor relay device according to the first aspect, 20 or more photodiode arrays are connected in series.

  According to a third aspect of the present invention, in the semiconductor relay device according to the first aspect, one or more diodes connected in series are formed in parallel with the photodiode array in the opposite direction.

  According to a fourth aspect of the present invention, in the semiconductor relay device according to the third aspect, the series-connected diodes are connected in parallel between the photodiode array and the charge / discharge circuit.

  According to a fifth aspect of the present invention, in the semiconductor relay device according to the third aspect, the series-connected diodes are connected in parallel between the charge / discharge circuit and the output MOSFET.

  According to a sixth aspect of the present invention, in the semiconductor relay device according to any one of the third to fifth aspects, a diode connected in parallel to the photodiode array is formed of polysilicon, and the diode, the photodiode array, and The charge / discharge circuit is integrated and formed.

  According to a seventh aspect of the present invention, in the semiconductor relay device according to any one of the first to sixth aspects, the output MOSFET is a MOSFET in which two MOSFETs are connected in reverse series.

  According to the invention of claim 1, since an output MOSFET composed of silicon carbide (SiC), which is a power device with high breakdown voltage, high thermal conductivity, and high efficiency, having performance exceeding the performance limit of Si material is used. Compared to a conventional semiconductor relay device using a Si semiconductor MOSFET, a compact, high-performance semiconductor relay device with higher withstand voltage, high heat resistance, and low loss can be obtained.

  According to the invention of claim 2, since a large predetermined voltage is obtained, the SiC-MOSFET that requires a high control voltage can be reliably driven by this predetermined voltage.

  According to the invention of claim 3, since the control voltage applied to the SiC-MOSFET is limited by the Zener action of the diode so that it is not higher than necessary, a large electric field stress is not applied to the SiC-MOSFET, and the output device The SiC-MOSFET can be protected from overvoltage, and the reliability of the semiconductor relay device can be improved.

  According to the invention of claim 4, in the photodiode array, the output voltage of the photodiode array is immediately limited by the Zener action of the directly connected diodes, so that the output from the photodiode array becomes a constant value at a higher speed. The SiC-MOSFET can also be stabilized more quickly.

  According to the fifth aspect of the present invention, the gate voltage of the SiC-MOSFET is limited by the Zener action of the diode directly connected to the gate, so that a safe voltage can be more reliably applied to the gate.

  According to the invention of claim 6, since the diode connected in parallel with the photodiode array can be planarly formed on the semiconductor substrate by forming it with polysilicon, it is necessary to form it in the semiconductor substrate. This eliminates the influence of parasitic elements or the like that normally occur when elements are formed on the same semiconductor substrate, thereby improving the reliability of the operation characteristics of each circuit element. In addition, since the diode, the photodiode array, and the charge / discharge circuit are integrally formed, the chip size can be reduced, the process can be simplified, and the circuit configuration of the semiconductor relay device can be made compact.

  According to the invention of claim 7, since both drain terminals of the two output SiC-MOSFETs which are output terminals of the semiconductor relay device are symmetric when viewed from the load side, one output SiC-MOSFET is an output terminal. Since it is necessary to connect the drain and the source corresponding to the high potential side and the low potential side of the load, the semiconductor relay device that can only switch the DC load can also switch the AC load in this configuration. Thereby, there is no polarity in the connection between the semiconductor relay device and the load, the degree of freedom of connection is increased, and the convenience for the user is improved.

  Hereinafter, a semiconductor relay device according to an embodiment of the present invention will be described with reference to FIG. The semiconductor relay device in this embodiment includes a light emitting diode 1 (LED, light emitting element) that outputs an optical signal in response to an input signal, and a photodiode array 2 that receives the optical signal from the LED 1 and generates a predetermined voltage. (Light receiving element), charge / discharge circuit 3 for charging / discharging the voltage generated by the photodiode array 2, and silicon carbide (SiC) that is turned on / off by a control voltage from the charge / discharge circuit 3 for output MOSFET 4 (referred to as SiC-MOSFET).

  The LED 1 emits an optical signal in response to input signals from the input terminals 11 and 12. The photodiode array 2 is a solar cell, receives an optical signal from the LED 11, induces an electromotive force, and generates a predetermined voltage. This predetermined voltage is supplied to the charge / discharge circuit 3 that charges and discharges the predetermined voltage.

  The charging / discharging circuit 3 includes a depletion type MOSFET 31 and an enhancement type MOSFET 32 for voltage control, and a resistor 33. The drain and gate of the MOSFET 31 are connected to the high potential side and the low potential side of the photodiode array 2, respectively. The The drain and source of the MOSFET 32 are connected to the source and gate of the MOSFET 31, respectively, and are short-circuited by the resistor 33, and the drain and gate are short-circuited.

  In the charge / discharge circuit 3, when a predetermined voltage from the photodiode array 2 is applied to the drain and gate of the MOSFET 31, the MOSFET 32 is turned on from off and the MOSFET 31 is turned off from on. At this time, a potential difference is generated between the gate and the source of the SiC-MOSFET 4, the gate is charged, and the SiC-MOSFET 4 is driven. Next, when the optical signal from the LED 11 is cut off, the MOSFET 32 is turned off and the MOSFET 31 is turned on from off in the same manner as described above. As a result, the potential difference between the gate and source of the SiC-MOSFET 4 disappears, the gate is discharged, and the SiC-MOSFET 4 is turned off. By providing this charging / discharging circuit 3, switching of charging / discharging of the SiC-MOSFET 4 is performed smoothly.

  When the control voltage from the charge / discharge circuit 3 is applied between the gate and the source of the SiC-MOSFET 4 based on the predetermined voltage generated when the input signal is turned on, the SiC-MOSFET 4 becomes conductive, and the external terminal 41 , 42 are conducted, and the relay is closed. When the input signal is turned off, the control voltage from the charging / discharging circuit 3 is lost, the SiC-MOSFET 4 is turned off, the external terminals 41 and 42 are cut off, and the relay is opened.

  By the way, the SiC-MOSFET 4 uses silicon carbide (SiC), which is a kind of compound semiconductor made of carbon and silicon, as a semiconductor material. This silicon carbide (SiC) has many excellent features such as a dielectric breakdown electric field of 10 times or greater, Si thermal conductivity 3 times, and saturation electron velocity 2 times greater than Si. In addition, since SiC has a band gap that is about three times that of Si, the operating temperature of SiC devices reaches about 400 ° C, and it is used at a temperature that is much higher than the operating temperature limit of 140 ° C for Si devices. Is possible. Further, since the SiC-MOSFET 4 has a high dielectric breakdown electric field, it has an extremely high breakdown voltage characteristic (for example, 1200 V or more) compared to a silicon MOSFET (referred to as Si-MOSFET), and has an on-resistance that is two orders of magnitude smaller than that of a Si semiconductor element. Since the speed is high, it is suitable for a switching element.

  As described above, the semiconductor relay device of the present embodiment uses a high breakdown voltage, high heat resistance, high efficiency, low loss SiC-MOSFET 4 having features superior to Si-MOSFET as an output MOSFET. The number of output MOSFETs connected in series can be reduced as compared with Si-MOSFETs, and the circuit configuration can be simplified and reduced in size. In addition, when operating at high temperatures, the operating temperature range can be up to about 400 ° C. compared to the operating temperature limit of 140 ° C. for Si semiconductors that are normally used. It can be eliminated and the entire device can be downsized. As described above, by using the SiC-MOSFET 4 as the output MOSFET, the semiconductor relay device can be remarkably increased in breakdown voltage, increased in temperature resistance, reduced in power consumption, and reduced in size.

  FIG. 2 shows a configuration of a semiconductor relay device according to the second embodiment of the present invention. In the present embodiment, in the first embodiment, the photodiode array 2 is configured by connecting 20 photodiodes in series, and further, between the photodiode array 2 and the charge / discharge circuit 3, a photodiode is arranged. A zener diode 5 is connected in parallel with the array 2 in the opposite direction. In FIG. 2, the same members as those of the first embodiment are denoted by the same reference numerals.

  The semiconductor relay device of this embodiment includes a light emitting diode 1 (LED) that outputs an optical signal in response to an input signal, a photodiode array 2 that receives an optical signal from the LED 1 and generates an electromotive force, A voltage limiting Zener diode 5 for limiting the output voltage of the photodiode array 2; a charging / discharging circuit 3 for charging / discharging the output voltage from the Zener diode 5; and a control voltage from the charging / discharging circuit 3; The output SiC-MOSFET 4 is turned off. Further, the Zener diode 5 is made of polysilicon and is formed integrally with the photodiode array 2 and the charge / discharge circuit 3.

  In this SiC-MOSFET 4, the bulk resistance component is small, but the channel resistance component is large. Therefore, in order to reduce the total resistance of the SiC-MOSFET 4, the channel is driven by a gate voltage larger than that of the Si-MOSFET. It is necessary to reduce the resistance component. Further, in order to reduce the channel resistance component, a gate voltage that reliably drives the SiC-MOSFET 4 of the output element of the semiconductor relay device is required, and thus a solar cell that can generate a large output voltage is required. For example, in the case of driving a Si-MOSFET, a gate voltage of about 5V is sufficient, but for driving a SiC-MOSFET, a gate voltage of 10V or more is required.

  Therefore, the photodiode array 2 is composed of solar cells in which 20 or more photodiodes are connected in series in order to obtain a gate voltage of 10 V or more. Usually, a photodiode generates an electromotive force of about 0.7 V at room temperature. Therefore, the photodiode array 2 generates an electromotive force of about 14 V by connecting 20 photodiodes in series, and the SiC-MOSFET 4 is reliably connected. To drive.

  The voltage of the photodiodes constituting the photodiode array 2 generally increases at a low temperature and decreases at a high temperature (generally, Si has a temperature gradient of about −2.3 mV / ° C.). For this reason, the difference in electromotive force greatly changes between high temperature and low temperature, and at low temperature, the output voltage of the photodiode array 2 increases, and an excessive voltage is applied to the gate of the SiC-MOSFET 4 to generate a large electric field at the gate. Risk of stress and problems with reliability. Further, when the temperature is high, the gate voltage becomes too low, and there is a possibility that the SiC-MOSFET 4 cannot be driven reliably.

  Therefore, in order to limit the gate voltage that rises at a low temperature, a Zener diode 5 that limits the voltage in parallel in the reverse direction is connected to the photodiode array 2. The relationship between the output voltage Eo of the photodiode array 2 and the temperature T in this case is shown in FIG. In FIG. 3, a line L1 indicates a temperature change of the output voltage Eo of the photodiode array 2, a dotted line L2 indicates an extension of the line L1 when the voltage of the line L1 is not limited, and a line L3 is 15V at the Zener diode 5. Is a voltage-limited output voltage Eo, and becomes a line at a constant level from the point A where the output voltage Eo of the line L1 indicates 15 V to the low temperature side.

  As shown in FIG. 3, the output voltage Eo is about 14 V at room temperature Ta, and at a low temperature Tb (about 130 ° C. lower than room temperature Ta), the zener diode 5 is used as shown by the dotted line L2 on the extension of the line L1. When not limited, the output voltage Eo rises to a voltage of about 20 V at the intersection B between the temperature Tb and the line L2. Here, by introducing the Zener diode 5, the output voltage Eo is limited to about 15V or less, so that the SiC-MOSFET 4 can be safely driven. On the other hand, at a high temperature Tc (about 90 ° C. higher than the room temperature Ta), the voltage drops to about 10 V. However, since the drive gate voltage of the SiC-MOSFET 4 only needs to be about 10 V, the SiC-MOSFET 4 can be driven reliably. In this way, the output voltage of the photodiode array 2 at room temperature is set to about 14V, and is set higher than the driveable gate voltage 10V of the SiC-MOSFET 4, and the Zener diode 5 is provided, so that the output voltage is high or low. However, the drive voltage range is ensured, and the SiC-MOSFET 4 can be driven reliably and stably.

  Further, the Zener diode 5 may be any diode as long as it has a voltage limiting action, and a plurality of diodes connected in series may be used. In addition, the Zener diode 5 can form a Zener voltage with higher accuracy than single crystal silicon by using polysilicon with good workability as a material. Further, since the Zener diode 5 is formed of polysilicon and is formed in a plane on the semiconductor substrate, it is not necessary to form it in the semiconductor substrate, and is usually used when forming an element in the same semiconductor substrate. The influence of the parasitic element which becomes a problem is eliminated, and the reliability in the relay operation characteristics can be improved. Further, by integrating the Zener diode 5, the photodiode array 2, and the charge / discharge circuit 3, the chip size can be reduced and the process can be simplified, and the circuit configuration of the relay device can be made compact.

  As described above, according to the present embodiment, 20 or more photodiodes are formed in series in the photodiode array 2 and connected to the Zener diode 5 in parallel in the opposite direction to the photodiode array 2. Even when the temperature is high, the output SiC-MOSFET 4 can be reliably driven, and a highly reliable semiconductor relay device can be formed.

  FIG. 4 shows a configuration of a semiconductor relay device according to the third embodiment of the present invention. In the second embodiment, the Zener diode 5 is connected in parallel in the opposite direction between the charge / discharge circuit 3 and the output SiC-MOSFET 4 in the second embodiment.

  The semiconductor relay device of this embodiment includes a light emitting diode 1 (LED) that outputs an optical signal in response to an input signal, a photodiode array 2 that receives the optical signal from the LED 1 and generates a predetermined voltage, ON / OFF by a charge / discharge circuit 3 for charging / discharging a predetermined voltage generated by the photodiode array 2, a voltage limiting Zener diode 5 for limiting the control voltage from the charging / discharging circuit 3, and a voltage limited control voltage, And an SiC-MOSFET 4 which is an output MOSFET to be turned off.

  With the above configuration, in the semiconductor relay device of the present embodiment, the gate voltage of the SiC-MOSFET is directly limited by the diode connected in parallel to the gate in the reverse direction, so that the gate voltage can be more reliably limited, -The MOSFET can be stably controlled, and a more reliable semiconductor relay device can be formed.

  FIG. 5 shows a configuration of a semiconductor relay device according to the fourth embodiment of the present invention. This embodiment is the same as the second embodiment except that the output MOSFETs are two SiC-MOSFETs connected in anti-series.

  The semiconductor relay device of this embodiment includes an LED 1 that outputs an optical signal in response to an input signal, a photodiode array 2 that receives an optical signal from the LED 1 and generates an electromotive force, and the photodiode array 2. A voltage limiting Zener diode 5 for limiting the generated electromotive force, a charging / discharging circuit 3 for charging / discharging the output of the Zener diode 5, and an output for turning on / off by a control voltage from the charging / discharging circuit 3. The SiC-MOSFET 4 includes two SiC-MOSFETs 4a and 4b connected in reverse series.

  In the SiC-MOSFETs 4a and 4b connected in reverse series, both source terminals are connected to be a common terminal, and each drain is connected to the external terminals 41 and 42 of the semiconductor relay device. The high potential side of the charge / discharge circuit 3 is connected to both gate terminals of the SiC-MOSFETs 4a and 4b, and the low potential side of the charge / discharge circuit 3 is connected to both source terminals. With this configuration, both ends 41 and 42 of the relay device are both connected to the drain terminal side of the SiC-MOSFETs 4a and 4b, and are symmetric as viewed from the load side, as compared with the case where there is one output SiC-MOSFET. Therefore, this semiconductor relay device can switch an AC load.

  According to the semiconductor relay device according to the various embodiments described above, the use of the SiC-MOSFET 4 having the characteristics of high breakdown voltage, high heat resistance, high efficiency, and low loss superior to that of the Si-MOSFET as the output MOSFET results in high breakdown voltage. In the relay, the number of output semiconductor elements can be reduced, and the circuit configuration can be simplified and reduced in size. In addition, when operating at high temperatures, the operating temperature range can be significantly increased compared to the operating temperature limits of Si semiconductors that are normally used. This makes it possible to simplify or eliminate the cooling device and to reduce the size of the entire device. . As described above, by using the SiC-MOSFET 4, the semiconductor relay device can be remarkably increased in breakdown voltage, increased in temperature, reduced in power consumption, and reduced in size.

  In addition, by forming 20 or more photodiodes in series in the photodiode array and connecting a Zener diode in parallel to the photodiode array in the reverse direction, the SiC-MOSFET for output can be reliably output at low and high temperatures. A highly reliable semiconductor relay device can be formed.

  In addition, by forming the Zener diode with polysilicon, the Zener diode is planarly formed on the semiconductor substrate, thereby eliminating the influence of parasitic elements and the like that cause problems when forming circuit elements on the same semiconductor substrate. The reliability in the relay operation characteristics is improved. In addition, the integrated formation of the Zener diode, the photodiode array, and the charge / discharge circuit can reduce the chip size and simplify the process, and can make the circuit configuration of the relay device compact.

  Further, by configuring the output SiC-MOSFETs to be connected in two anti-series, the AC load can be switched, the polarity between the connection of the semiconductor relay and the load is eliminated, and the degree of freedom of connection is increased. .

  The present invention is not limited to the above embodiment, and various modifications can be made. The Zener diode may be a diode other than the Zener diode as long as it is a voltage-limiting diode, and the optical signal can be enhanced by using a plurality of LEDs. In addition, by forming a plurality of SiC-MOSFETs in series, a semiconductor relay device having a higher breakdown voltage can be formed.

The circuit block diagram of the semiconductor relay apparatus which concerns on the 1st Embodiment of this invention. The circuit block diagram of the semiconductor relay apparatus which concerns on the 2nd Embodiment of this invention. The figure which shows the temperature characteristic of the output voltage of the photodiode array in the said apparatus. The circuit block diagram of the semiconductor relay apparatus which concerns on the 3rd Embodiment of this invention. The circuit block diagram of the semiconductor relay apparatus which concerns on the 4th Embodiment of this invention.

Explanation of symbols

1 Light-emitting diode (light-emitting element)
2 Photodiode array (light receiving element)
3 Charge / Discharge Circuit 4, 4a, 4b SiC-MOSFET (Output MOSFET)
5 Zener diode (diode)

Claims (7)

A light emitting element that outputs an optical signal in response to an input signal, a photodiode array that receives an optical signal from the light emitting element and generates a predetermined voltage, and a charge / discharge circuit that charges and discharges a voltage generated by the photodiode array And an output MOSFET controlled by the charge / discharge circuit, and a semiconductor relay device that opens and closes the output MOSFET in response to the input signal,
The output MOSFET is made of silicon carbide (SiC), and is a semiconductor relay device.   The semiconductor relay device according to claim 1, wherein the photodiode array includes 20 or more photodiodes connected in series.   2. The semiconductor relay device according to claim 1, wherein one or more diodes connected in series are connected in parallel in the opposite direction to the photodiode array.   4. The semiconductor relay device according to claim 3, wherein the series-connected diodes are connected in parallel between the photodiode array and the charge / discharge circuit.   The semiconductor relay device according to claim 3, wherein the series-connected diodes are connected in parallel between the charge / discharge circuit and the output MOSFET.   6. The diode connected in parallel with the photodiode array is formed of polysilicon, and the diode, the photodiode array, and a charge / discharge circuit are formed integrally. The semiconductor relay apparatus in any one.   The semiconductor relay device according to claim 1, wherein the output MOSFET is two MOSFETs connected in anti-series.