JP2007281934A - Semiconductor relay - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor relay in which even when the impurity concentration of a base is increased for reducing a leak current between the drain and source of an output stage MOSFET, a gate threshold voltage Vt or ON resistance Ron is not increased and a switching time is not increased or ON resistance is not increased, as a result. <P>SOLUTION: A semiconductor relay 101 of the present invention comprises an LED 17 which converts an electric signal into an optical signal, a first photodiode array 18 which generates a first output voltage corresponding to the optical signal, and output stage MOSEFET 102, 103 of which a first output voltage is applied between a gate and a source to switch to a conducted/non-conducted state between the drain and the source, wherein a switching means 104 is provided for switching the gate threshold voltage of the output stage MOSFET 102, 103 between the conducted and non-conducted states. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor relay, and more particularly to a semiconductor relay including a double diffusion MOSFET as a switching element for turning on and off the semiconductor relay.

  As a relay that replaces the conventional electromagnetic relay, an electrical signal is converted into an optical signal by a light emitting element, and the optical signal is converted into an output voltage by a photovoltaic element optically coupled to the light emitting element, and this output voltage is used as a switching element. 2. Description of the Related Art A semiconductor relay that drives a MOSFET is known.

  An example of a conventional semiconductor relay will be described with reference to FIG. 6 showing a circuit diagram.

  In FIG. 6, 10 is a normally-off type semiconductor relay, 17 is an LED as a light emitting element, 16a and 16b are power terminals of the LED 17, 18 is a photodiode array as a photovoltaic element, 20 is a discharge circuit, and 20a and 20b are Diodes, 20c are thyristors, 21a and 21b are output terminals of the discharge circuit 20, 22 and 23 are double diffusion type enhancement type n-channel MOSFETs (hereinafter referred to as output stage MOSFETs) as switching elements, and 24a and 24b are semiconductors. This is an output terminal of the relay 10.

  A photodiode array 18 is disposed so as to be optically coupled to the LED 17. The photodiode array 18 is composed of k photodiodes connected in series.

  The output voltage of the photodiode array 18 generates an output voltage (DC voltage; A × k [V]) k times the electromotive voltage A [V] of each photodiode.

  The anode / cathode of the photodiode array 18 is connected to the discharge circuit 20.

  One output terminal 21a of the discharge circuit 20 is connected to a commonly connected gate of the two output stage MOSFETs 22 and 23, and the other output terminal 21b is a commonly connected source of the two output stage MOSFETs 22 and 23. It is connected to the.

  The drains of the two output stage MOSFETs 22 and 23 are connected to the output terminals 24a and 24b of the semiconductor relay 10, respectively.

  The discharge circuit 20 includes diodes 20a and 20b and a thyristor 20c.

  The anode of the diode 20 a is connected to the anode of the photodiode array 18, and the cathode of the diode 20 a is connected to the commonly connected gates of the output stage MOSFETs 22 and 23.

  The cathode of the diode 20 b is connected to the cathode of the photodiode array 18, and the anode of the diode 20 b is connected to the commonly connected sources of the output stage MOSFETs 22 and 23.

  The anode of the thyristor 20c is connected to the cathode of the diode 20a, the cathode of the thyristor 20c is connected to the anode of the diode 20b, the N-pole gate is connected to the anode of the diode 20a, and the P-pole gate is connected to the cathode of the diode 20b. Yes.

  In the discharge circuit 20 configured as described above, when the photodiode array 18 generates an output voltage, the thyristor 20c is in an off state, and the charge is applied to the gates of the output stage MOSFETs 22 and 23 through the diodes 20a and 20b.

  When the output voltage of the photodiode array 18 disappears, the gate voltages of the output stage MOSFETs 22 and 23 are held as they are by the diodes 20a and 20b and the thyristor 20C, but the voltage in the photodiode array 18 decreases due to self-discharge.

  Due to this voltage drop, the voltage difference between the anode / cathode of the diodes 20a, 20b becomes large, the N-pole gate or the P-pole gate is biased in the forward direction, and the thyristor 20c is turned on.

  Due to the self-holding characteristics of the thyristor 20c, the ON state is maintained until the potential between the anode and the cathode drops to about 1V. For this reason, the electric charge accumulated in the gate is quickly discharged through the thyristor 20C. However, the discharge circuit is not limited to this.

  Here, as shown in FIG. 7, the bases and sources of the output stage MOSFETs 22 and 23 are normally short-circuited. This is to prevent a parasitic transistor composed of drain (n), base (p), and source (n) from operating when a high voltage is applied between the drain and the source, thereby reducing the breakdown voltage when turned off. It is. FIG. 7 is a schematic cross-sectional view of the output stage MOSFETs 22 and 23.

  In addition, since a parasitic diode (not shown) is generated between the base and drain of the double diffusion type MOSFET, the two MOSFETs are reversely connected so that a complementary switching operation is possible for bidirectional energization. ing.

  In the above description, the semiconductor relay 10 is described as an example for bidirectional energization in which the two output stage MOSFETs 22 and 23 are reversely connected (source / source connection, gate / gate connection, connection form in which each drain is an output). As shown in FIG. 8, there is also a unidirectional energization semiconductor relay 30 constituted by one output stage MOSFET 22.

  Further, the output stage MOSFETs 22 and 23 may be horizontal MOSFETs or vertical MOSFETs.

  In the above description, the semiconductor relay is described as an example of a normally-off type, but a normally-on type semiconductor relay may be used. However, the output stage MOSFET is a depletion type n-channel MOS, and the connection of the first photodiode array 17 is inverted so that the gate-source voltage application direction is negative on the gate side and positive on the source side.

  Next, the operation of the semiconductor relay 10 for bidirectional energization will be described with reference to FIG. Note that the semiconductor relay 30 for unidirectional energization is the same as the semiconductor relay 10 for bidirectional energization except that there is only one output stage MOSFET, and is omitted.

  First, when an electric signal is applied between the power supply terminals 16a and 16b, the LED 17 emits light.

  This optical signal is received by the photodiode array 18 and an output voltage (DC voltage; A × k [V]) is generated at both ends thereof.

  This output voltage is supplied between the gate and source of the two output stage MOSFETs 22 and 23 that are commonly connected via the output terminals 21a and 21b.

  As a result, the two output stage MOSFETs 22 and 23 become conductive.

  When the two output stage MOSFETs 22 and 23 are both in a conductive state, the output terminals 24a and 24b of the semiconductor relay 10 are in a conductive state, that is, the semiconductor relay 10 is in an on state.

  Next, when an electric signal is no longer applied between the input terminals 16a and 16b, the LED 17 stops emitting light.

  As a result, the photodiode array 18 does not receive light, and the output voltage (DC voltage; A × k [V]) generated at both ends thereof is eliminated.

  For this reason, there is no voltage between the output terminals 21a and 21b.

  Also, the voltage between the gate and source connected in common to the two output stage MOSFETs 22 and 23 is eliminated.

  As a result, the two output stage MOSFETs 22 and 23 become non-conductive.

  When the two output stage MOSFETs 22 and 23 are both in a non-conductive state, the output terminals 24a and 24b of the semiconductor relay 10 are in a non-conductive state, that is, the semiconductor relay 10 is in an off state.

The discharge circuit 20 quickly discharges the electric charge accumulated between the gate and the source of the two output stage MOSFETs 22 and 23 that are commonly connected in the ON state of the semiconductor relay 10. Thereby, the semiconductor relay 10 is quickly switched from the on state to the off state. (For example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 2004-6778 FIG.

  In the conventional semiconductor relay 10, the leakage current between the drain and source of the output stage MOSFETs 22 and 23 as switching elements mainly becomes the leakage current between the output terminals 24 a and 24 b of the semiconductor relay 10. In applications such as thousands of semiconductor testers (not shown) connected in parallel, there was a problem that the leakage current increased several thousand times and adversely affected the measurement accuracy of the semiconductor tester (not shown). .

  Usually, in order to reduce the leakage current between the drain and source of such a MOSFET, there are methods such as increasing the impurity concentration of the base of the output stage MOSFET, increasing the channel length, and narrowing the channel width. It is well known.

  However, if the impurity concentration of the base is increased, the channel length is increased, or the channel width is decreased, the gate threshold voltage Vt of the output stage MOSFET increases, and accordingly, the switching time of the semiconductor relay 10 increases, The on-resistance Ron of the output stage MOSFET increased, and the on-resistance of the semiconductor relay 10 increased accordingly. The gate threshold voltage Vt is a voltage applied to the gate when a predetermined current value flows between the drain and the source.

  The problem of the present invention is that the gate threshold voltage Vt and the on-resistance Ron do not increase even if the impurity concentration of the base is increased in order to reduce the leakage current between the drain and source of the output stage MOSFET. It is an object of the present invention to provide a semiconductor relay that does not increase or increase on-resistance.

  The semiconductor relay of the present invention includes a light emitting element that converts an electrical signal into an optical signal, a first photovoltaic element that generates a first output voltage corresponding to the optical signal, and a first output voltage that is a gate / source. A semiconductor relay including a double diffusion type MOSFET that is applied between and switched between a drain and a source in a conductive / non-conductive state, and includes a switching means for switching the gate threshold voltage of the MOSFET in a conductive / non-conductive state This is a semiconductor relay characterized by that.

  According to the semiconductor relay of the present invention, the gate threshold voltage Vt and the on-resistance Ron do not increase even if the base impurity concentration is increased in order to reduce the drain-source leakage current of the output stage MOSFET. It is possible to provide a semiconductor relay in which switching time does not increase and on-resistance does not increase.

  The present invention provides a semiconductor relay that does not increase switching time or increase on-resistance even if the impurity concentration of the base is increased to reduce the leakage current between the drain and source of the output stage MOSFET. This object has been realized by providing switching means for switching the gate threshold voltage of the MOSFET between a conductive state and a non-conductive state.

  An example of the semiconductor relay of the present invention will be described with reference to FIG. The same parts as those in FIG.

  In FIG. 1, 101 is a normally-off type semiconductor relay of the present invention, 17 is an LED as a light emitting element, 16a and 16b are power terminals of the LED 17, 18 is a first photodiode array as a first photovoltaic element, 20 is a discharge circuit, 20a and 20b are diodes, 20c are thyristors, 21a and 21b are output terminals of the discharge circuit 20, and 102 and 103 are double diffusion type enhancement type n-channel MOSFETs (hereinafter referred to as the first switching elements). 24a and 24b are output terminals of the semiconductor relay 101, 104 is a switching means that is a feature of the present invention, 105 is a second photodiode array as a second photovoltaic element, and 106 is a first output element. 2 is a depletion type MOSFET as a switching element.

  A first photodiode array 18 is arranged in optical coupling with the LED 17. The first photodiode array 18 is configured by k photodiodes connected in series.

  The output voltage of the first photodiode array 18 generates a first output voltage (DC voltage; A × k [V]) that is k times the electromotive voltage A [V] of each photodiode.

  The anode / cathode of the first photodiode array 18 is connected to the discharge circuit 20.

  One output terminal 21 a of the discharge circuit 20 is connected to a commonly connected gate of the two output stage MOSFETs 102 and 103, and the other output terminal 21 b is a commonly connected source of the two output stage MOSFETs 102 and 103. It is connected to the.

  The drains of the two output stage MOSFETs 102 and 103 are connected to the output terminals 24a and 24b of the semiconductor relay 101, respectively.

  The discharge circuit 20 includes diodes 20a and 20b and a thyristor 20c.

  The anode of the diode 20a is connected to the anode of the first photodiode array 18, and the cathode of the diode 20a is connected to the commonly connected gates of the output stage MOSFETs 102 and 103.

  The cathode of the diode 20 b is connected to the cathode of the first photodiode array 18, and the anode of the diode 20 b is connected to the commonly connected sources of the output stage MOSFETs 102 and 103.

  The anode of the thyristor 20c is connected to the cathode of the diode 20a, the cathode of the thyristor 20c is connected to the anode of the diode 20b, the N-pole gate is connected to the anode of the diode 20a, and the P-pole gate is connected to the cathode of the diode 20b. Yes.

  The discharge circuit 20 configured as described above applies charges to the gates of the output stage MOSFETs 102 and 103 when the photodiode array 18 generates an output voltage. When the output voltage is lost, the charge accumulated in the gates is transferred to the thyristor. Discharge quickly through 20C. However, the discharge circuit is not limited to this.

  Further, the switching means 104 which is a feature of the present invention is connected to the subsequent stage of the discharge circuit 20.

  The switching means 104 includes a second photodiode array 105 as a second photovoltaic element and a depletion type MOSFET 106 as a second switching element.

  The second photodiode array 105 includes m photodiodes connected in series, and a second output voltage (DC voltage; A × m [V] that is m times the electromotive voltage A [V] of each photodiode. ]).

  If the first photodiode array 17 and the second photodiode array 105 are photodiode arrays having the same response speed, good synchronization may be obtained.

  Further, the second output voltage (A × m [V]) is a gate threshold voltage Vt generated by increasing the impurity concentration of the base in order to reduce the drain-source leakage current of the output stage MOSFET. Set to offset the increase.

  The cathode of the second photodiode array 105 is connected to the commonly connected base of the two output stage MOSFETs 102 and 103, and the anode is connected to the commonly connected source of the two output stage MOSFETs 102 and 103, respectively. .

  The depletion type MOSFET 106 has its gate connected to the output terminal 21 a and is connected to the commonly connected gates of the two output stage MOSFETs 102 and 103.

  The source (or drain) is connected to the cathode of the second photodiode array 105 and is connected to the commonly connected bases of the two output stage MOSFETs 102 and 103.

  Further, the drain (or source) is connected to the anode of the second photodiode array 105 and is connected to the commonly connected sources of the two output stage MOSFETs 102 and 103.

  The depletion type MOSFET 106 connected in this way is turned off when there is a gate input signal, and the output voltage generated by the second photodiode array 105 is connected to the bases of the two output stage MOSFETs 102 and 103 connected in common. When it is applied between the sources and there is no gate input signal, it is turned on to short-circuit between the base and the source connected in common to the two output stage MOSFETs 102 and 103, respectively.

  In the above description, the semiconductor relay 101 is described as an example for bidirectional energization in which the two output stage MOSFETs 102 and 103 are reversely connected (source / source connection, gate / gate connection, connection form in which each drain is an output). As shown in FIG. 2, the semiconductor relay 201 for unidirectional energization may be composed of a single output stage MOSFET 102.

  The output stage MOSFETs 102 and 103 may be horizontal MOSFETs or vertical MOSFETs.

  In the above description, the semiconductor relay is described as an example of a normally-off type, but a normally-on type semiconductor relay may be used.

  However, the output stage MOSFET is a depletion type n-channel MOS, and the connection of the first photodiode array 17 is reversed so that the gate-source voltage application direction is negative on the gate side and positive on the source side. The connection of the photodiode array 105 is inverted so that the voltage application direction between the base and source is negative on the source side and positive on the base side.

  Next, the operation of the semiconductor relay 101 for bidirectional energization will be described with reference to FIGS. The semiconductor relay 201 for unidirectional energization is the same as the semiconductor relay 101 for bidirectional energization except that there is only one output stage MOSFET, and is omitted.

  First, the on state of the semiconductor relay 101 will be described with reference to FIG.

  When an electric signal is applied between the power supply terminals 16a and 16b, the LED 17 emits light.

  This optical signal is received by the first photodiode array 18 and a first output voltage (DC voltage; A × k [V]) is generated at both ends thereof.

  This output voltage is supplied between the gate and the source of the two output stage MOSFETs 102 and 103 that are commonly connected via the output terminals 21a and 21b.

  As a result, the two output stage MOSFETs 102 and 103 become conductive.

  When the two output stage MOSFETs 102 and 103 are both in a conductive state, the output terminals 24a and 24b of the semiconductor relay 101 are in a conductive state, that is, the semiconductor relay 101 is in an on state.

  At this time, since the input signal (DC voltage) generated in the first photodiode 18 is also applied to the gate of the depletion type MOSFET 106 of the switching means 104, the depletion type MOSFET 106 is turned off.

  The second photodiode array 105 of the switching unit 104 also receives the light simultaneously with the first photodiode array 18 to generate a second output voltage (DC voltage; A × m [V]).

  The voltage application state of the output stage MOSFETs 102 and 103 at this time will be described with reference to a schematic cross-sectional view shown in FIG. That is, the second output voltage (DC voltage; A × m [V]) is the base connected to each of the two output stage MOSFETs 102 and 103 in common because the depletion type MOSFET 106 is in a non-conductive state (off state). • Applied between sources. The voltage application direction is positive on the source side and negative on the base side, and a voltage in a direction to reduce the gate threshold voltage Vt is applied.

  Next, the off state of the semiconductor relay 101 will be described with reference to FIG.

  When the electric signal is no longer applied between the input terminals 16a and 16b, the LED 17 stops emitting light.

  As a result, the first photodiode array 18 does not receive light, and the first output voltage (DC voltage; A × k [V]) generated at both ends thereof is eliminated.

  For this reason, there is no voltage between the output terminals 21a and 21b.

  Further, the voltage between the gate and the source connected in common to each of the two output stage MOSFETs 102 and 103 is also eliminated.

  As a result, the two output stage MOSFETs 102 and 103 are turned off.

  When the two output stage MOSFETs 102 and 103 are both in a non-conducting state, the output terminals 24a and 24b of the semiconductor relay 101 are in a non-conducting state, that is, the semiconductor relay 101 is in an off state.

  The discharge circuit 20 quickly discharges the electric charge accumulated between the gate and the source connected in common to the two output stage MOSFETs 102 and 103 when the semiconductor relay 101 is on. Thereby, the semiconductor relay 101 is quickly switched from the on state to the off state.

  At this time, the input signal (DC voltage) generated in the first photodiode 18 is not applied to the gate of the depletion type MOSFET 106 of the switching means 104, and the depletion type MOSFET 106 becomes conductive.

  The voltage application state of the output stage MOSFETs 102 and 103 at this time will be described with reference to a schematic cross-sectional view shown in FIG. That is, when the depletion type MOSFET 106 becomes conductive, the base and source connected in common to the two output stage MOSFETs 102 and 103 are short-circuited.

  As described above, when the semiconductor relay 101 is in the OFF state, the base and source of each of the output stage MOSFETs 102 and 103 are short-circuited, and when a high voltage is applied between the drain and source, the drain (n) and base (p ). A parasitic transistor composed of the source (n) operates to prevent the breakdown voltage at the time of OFF from being lowered.

  The present invention can be applied to a semiconductor relay that can reduce the leakage current between output terminals without increasing the switching time or increasing the on-resistance.

Circuit diagram of an example of the semiconductor relay of the present invention Circuit diagram of another example of semiconductor relay of the present invention The circuit diagram which shows the ON state of the semiconductor relay of this invention The circuit diagram which shows the OFF state of the semiconductor relay of this invention Schematic sectional view of an output stage MOSFET of a semiconductor relay of the present invention Circuit diagram of an example of a conventional semiconductor relay Schematic cross-sectional view of a conventional semiconductor relay output stage MOSFET Circuit diagram of another example of conventional semiconductor relay

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Conventional semiconductor relay 16a, 16b Power supply terminal of light emitting element 17 LED
18 (first) photodiode array 20 discharge circuit 20a, 20b diode 20c thyristor 21a, 21b output terminal of discharge circuit 22, 23, 102, 103 output stage MOSFET
24a, 24b Semiconductor relay output terminal 30 Conventional semiconductor relay for unidirectional energization 101 Semiconductor relay 104 of the present invention 104 Switching means 105 Second photodiode array 106 Depletion type MOSFET
201 Semiconductor relay for unidirectional energization of the present invention A Electromotive voltage of individual photodiodes k Number of second photodiode arrays m Number of first photodiode arrays Ron On resistance Vt Gate threshold voltage

Claims (8)

  A light emitting element that converts an electrical signal into an optical signal, a first photovoltaic element that generates a first output voltage corresponding to the optical signal, and the first output voltage applied between a gate and a source A semiconductor relay including a double diffusion type MOSFET in which a drain and a source are switched to a conductive / non-conductive state, and includes a switching means for switching a gate threshold voltage of the MOSFET in the conductive / non-conductive state. A featured semiconductor relay.   The switching means applies a voltage in a direction to reduce the gate threshold voltage between the base and the source when the drain and the source are conductive, and shorts the base and the source when the drain and the source are not conductive. The semiconductor relay according to claim 1.   The switching means switches between application / non-application of the second photovoltaic element connected between the base and the source and the second output voltage generated by the second photovoltaic element between the base and the source. The semiconductor relay according to claim 1, further comprising a second switching element.   The semiconductor relay according to claim 3, wherein the first and second photovoltaic elements are photovoltaic elements having the same response speed.   The semiconductor relay according to claim 3 or 4, wherein the first and second photovoltaic elements are both photodiode arrays.   The semiconductor relay according to claim 3, wherein the second switching element is a normally-on type FET.   7. A normally-off type semiconductor relay, wherein when the MOSFET is an enhancement-type n-channel MOS, the voltage application direction for reducing the gate threshold voltage is positive on the source side and negative on the base side. The semiconductor relay in any one of.   3. A normally-on type semiconductor relay, wherein when the MOSFET is a depletion type n-channel MOS, the voltage application direction for reducing the gate threshold voltage is negative on the source side and positive on the base side. The semiconductor relay according to any one of 6.

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