JPH1154784A - Semiconductor relay - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect an output MOSFET against damage. SOLUTION: A semiconductor relay is composed of a light emitting device 1 which emits light according to input signals, a photodetector 2 which generates a photovoltaic power receiving light emitted from the light emitting device 1, output MOSFETs 3 and 3 where an impedance between a drain and a source becomes low when a voltage difference between a gate and a source exceeds a threshold value at the time when a photovoltaic power generated by the photodetector 2 is applied to charge them with electricity, a control means 40 which includes a control transistor 7 connected between the gate and source of the MOSFETs 3 and 3 and controls the electric charge and discharge of the MOSFETs 3 and 3, overcurrent detection resistors 5 and 5 connected to the sources of the MOSFETs 3 and 3 respectively, bipolar transistors 4 and 4 whose collectors are connected to the gates of the MOSFETs 3 and 3, and diodes 6 and 6 which form connection circuits 30 and 30 connected to the overcurrent detection resistors 5 and 5 in parallel together with the base-emitter parts of the bipolar transistors 4 and 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor relay for suppressing a current supplied to a MOSFET to a predetermined current or less.

[0002]

2. Description of the Related Art Conventionally, there is a semiconductor relay of this type shown in FIG. The light-emitting element A emits light in response to an input signal, the light-receiving element B receives light from the light-emitting element A to generate photovoltaic power, and the photovoltaic power generated by the light-receiving element B is applied. An output MOSFET C that changes from a high impedance state to a low impedance state between the drain and source when the voltage between the gate and the source exceeds the threshold value due to the charge;
Output MOSFET includes a control transistor D ₁ which in conjunction with the generation and disappearance of the photovoltaic by the connected light receiving element B between the gate and the source impedance state change of TC
C means for controlling the charge and discharge of the electric charge in C; an overcurrent detection resistor E connected to the source of the output MOSFET C; and a collector connected to the output MOSFET C and an overcurrent detection resistor connected between the base and the emitter. And a bipolar transistor F connected in parallel with E.

Next, the operation will be described. When the light emitting element A emits light according to the input signal, the light receiving element B receives the light of the light emitting element A and generates a photovoltaic voltage. Then, output M
OSFETC is charged by the application of photovoltaic voltage between its gate and source, the state between the drain and source changes from a high impedance state to a low impedance state, and a drain current flows.

When the drain current exceeds a predetermined current, the voltage across the overcurrent detecting resistor E connected to the source of the output MOSFET C increases, and the base E is connected to the overcurrent detecting resistor E. The base current of the bipolar transistor F flows, and the collector current of the bipolar transistor F flows. When the collector current of the bipolar transistor F flows in this way, the charge charged in the output MOSFET C is discharged, and the drain current of the output MOSFET C is suppressed to a predetermined current.

[0005]

In the above-described conventional semiconductor relay, when the drain current of the output MOSFET C exceeds a predetermined current, as described above, the drain current of the output MOSFET C becomes the predetermined current. Therefore, it is possible to prevent the drain current exceeding the predetermined current from continuing to flow through the output MOSFET C.

However, if the drain current of the output MOSFET C kept at a predetermined current continues to flow for a long time, the output MOSFET C may be damaged.

The present invention has been made in view of the above points, and an object of the present invention is to provide a semiconductor relay in which an output MOSFET is not damaged.

[0008]

In order to solve the above-mentioned problems, the present invention is directed to a light-emitting element which emits light in response to an input signal, and a photo-electromotive force generated by receiving light from the light-emitting element. And the drain-source changes from a high-impedance state to a low-impedance state when the voltage between the gate and the source exceeds a threshold value by applying a photoelectromotive force generated by the light-receiving element and charging the electric charge. An output MOSFET, and a control transistor connected between the gate and the source of the output MOSFET, the control state of which changes in impedance state in response to the generation and disappearance of photoelectromotive force by the light receiving element, and controls the charge and discharge of charges in the output MOSFET. Control means, an overcurrent detection resistor connected to the source of the output MOSFET, and a collector
The configuration includes a bipolar transistor connected to the gate of the FET, and a diode having a connection circuit connected in parallel with the overcurrent detection resistor between the base and the emitter of the bipolar transistor.

According to a second aspect of the present invention, in the first aspect of the present invention, the cathode of the diode is connected to a base of the bipolar transistor to form the connection circuit together with the bipolar transistor.

According to a third aspect of the present invention, in the first aspect of the present invention, the overcurrent detecting resistor and the diode are both provided on a silicon single crystal region of a silicon substrate. Wherein the overcurrent detecting resistor and the diode are provided on the same silicon single crystal region.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the overcurrent detecting resistor is made of polysilicon.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. This semiconductor relay includes a light emitting diode (light emitting element) 1, a photodiode array (light receiving element) 2, an output MOSFET 3, 3, an NPN bipolar transistor 4, 4, an overcurrent detecting resistor 5, 5, a temperature detecting diode 6, A control MOSFET 7 and a control resistor 8 are provided, and the photodiode array 2
PN bipolar transistors 4,4, overcurrent detection resistor 5,
5. The control MOSFET 7, the control resistor 8, and the temperature detecting diode 6 are provided on the same silicon substrate 10.

The light emitting diode (light emitting element) 1 emits an optical signal according to an input signal input between the input terminals 20a and 20b. The photodiode array (light receiving element) 2
A plurality of photodiodes 2a are provided on a silicon substrate 10 and are connected in series. The photodiodes 2a receive an optical signal from the light emitting diode 1 and generate a photoelectromotive force.

Each of the output MOSFETs 3, 3 is of an n-channel enhancement type, and has its gate connected to the anode of the photodiode array 2,
The drain is connected to the output terminal 20c on the power supply (not shown) side, and the source is connected via the overcurrent detection resistor 5 to the output terminal 20d on the load (not shown) side.

The overcurrent detecting resistors 5, 5 are made of polysilicon provided on a silicon single crystal region, and one end of each is connected to the source of the output MOSFET 3, 3, and the other end is controlled. Connected to the source of MOSFET7.

The bases of the NPN bipolar transistors 4, 4 are connected to one ends of overcurrent detecting resistors 5, 5 via a temperature detecting diode 6, respectively. For more information,
The respective bases of the NPN bipolar transistors 4, 4 are connected to the cathode of the temperature detecting diode 6. The emitters of the NPN bipolar transistors 4, 4 are connected to the other ends of the overcurrent detecting resistors 5, 5, respectively. In other words, the temperature detecting diode 6 forms a connection circuit 30 connected in parallel with the overcurrent detecting resistor 5 between the base and the emitter of the NPN bipolar transistors 4,4. Also, this NPN bipolar transistor
The collectors of 4,4 are connected to the gates of output MOSFETs 3,3.

The control MOSFET 7 is of an n-channel normally-closed type, and has an MO
The control means 40 controls charge and discharge of the SFET. The control MOSFET 7 has its gate connected to the source via the control resistor 8 and connected to the cathode of the photodiode array 2, and its source connected to the cathode of the photodiode array 2 via the control resistor 8. The drain is connected to the gates of the output MOSFETs 3,3.

The temperature detecting diode 6 is provided on the same silicon single crystal region as the overcurrent detecting resistors 5,5.

Next, the operation will be described. Light-emitting diode 1
Emits an optical signal according to the input signal, the photodiode array 2 receives the optical signal of the light emitting diode 1 and generates a photovoltaic voltage. With this photovoltaic power, the output MO
An electric charge is charged between the gate and the source of the SFET3, and a current flows between the drain and the source of the control MOSFET7. When a current flows through the control resistor 8 in this manner, a potential difference is generated between both ends of the control resistor 8, and the potential difference cuts off the drain and source of the control MOSFET 7 and the gate and source of the output MOSFET 3 In between the charge will be charged efficiently,
The state between the drain and the source of the output MOSFET 3 shifts from the high impedance state to the low impedance state. That is, the drain current of the output MOSFET 3 flows.

When no input signal is input to the light emitting diode 1 and light emission stops, the photodiode array 2 stops generating photovoltaic power. Then, the potential difference does not occur at both ends of the control resistor 8, the state between the drain and the source of the control MOSFET 7 changes to a conductive state, and the charge charged between the gate and the source of the output MOSFET 3 is discharged. , Is quickly discharged through the drain and source of the control MOSFET 7 and the output M
The state between the drain and the source of OSFET3 shifts to a high impedance state. That is, the output MOSFET 3
No drain current flows.

When the drain current of the output MOSFET 3 exceeds a predetermined current, the output MOSFET 3
Both ends of the overcurrent detection resistor 5 connected to the source of
The connection circuit 30 connected in parallel to the overcurrent detecting resistor 5 is connected to the NPN bipolar transistor 4 by a potential difference for causing the base current to flow enough to allow the collector current to flow by changing the emitter-collector of the NPN bipolar transistor 4 to a low impedance state. A potential difference is generated by adding a potential difference for flowing a current in the forward direction of the temperature detecting diode 6 formed between the base and the emitter of the NPN bipolar transistor.
4 collector current starts to flow. Thus, NP
When the collector current of the N bipolar transistor 4 flows, the charge charged between the gate and the source of the output MOSFET 3 is discharged, and the drain current of the output MOSFET 3 is suppressed to a predetermined current.

In such a semiconductor relay, as described above, when a current exceeding a predetermined current flows through the overcurrent detection resistor 5, the voltage across the overcurrent detection resistor 5 increases, and the NPN bipolar transistor 4, the electric charge charged in the output MOSFET 3 is discharged, and the drain current of the output MOSFET 3 is suppressed to a predetermined current. At this time, since the overcurrent detection resistor 5 generates heat, the temperature detection diode 6 forming the connection circuit 30 together with the base and emitter of the NPN bipolar transistor 4 also generates heat, and a current flows in the forward direction of the temperature detection diode 6. Since the potential difference for flowing decreases, the overcurrent detection resistor
5, the drain current becomes smaller than a predetermined current in conjunction with the decrease of the voltage across the overcurrent detection resistor 5, and the output MOSFET 3 is hardly damaged.

The temperature detecting diode 6 has its cathode connected to the base of the NPN bipolar transistor 4, its anode connected to the emitter of the NPN bipolar transistor 4, and the collector current of the NPN bipolar transistor 4. Does not affect the flow of the collector current and does not affect the discharge of the charge between the gate and the source of the output MOSFET 3.

Further, since the temperature detecting diode 6 is provided on the silicon single crystal region on which the overcurrent detecting resistor 5 is provided, the heat of the overcurrent detecting resistor 5 generated by energization is reduced. Conduction is facilitated, and the second potential difference for flowing a current in the forward direction of the temperature detecting diode 6 is easily reduced, so that the drain current is easily reduced and the output MOSFET 3 is less likely to be damaged. Become.

The overcurrent detecting resistor 5 is not a diffusion resistor whose resistance decreases with a rise in temperature, but is made of polysilicon whose resistance increases with a rise in temperature. In conjunction with the decrease in the voltage between both ends, the drain current is easily reduced, and the effect that the output MOSFET 3 is hardly damaged is easily exerted.

In this embodiment, the temperature detecting diode 6 has its cathode connected to the base of the bipolar transistor. However, even if its anode is connected to the emitter of the bipolar transistor, the output MOSF
This has the effect of making it difficult for the ET3 to be damaged.

In this embodiment, the overcurrent detecting resistor is used.
5 and the temperature detecting diode 6 are provided on the same silicon single crystal region.For example, when the heat generated by the overcurrent detecting resistor 5 is sufficiently transmitted to the temperature detecting diode 6, a different silicon is used. It may be provided on a single crystal region.

In this embodiment, the overcurrent detecting resistor is used.
5 is made of polysilicon, but is not limited to polysilicon.

In this embodiment, the bipolar transistor is an NPN bipolar transistor. However, the connection circuit may be appropriately changed to a PNP bipolar transistor.

In this embodiment, an output MOSFET is used.
3, an NPN bipolar transistor 4 and an overcurrent detection resistor 5 are two AC semiconductor relays each provided with two output MOSFETs 3, one NPN bipolar transistor 4 and one overcurrent detection resistor 5. The same effect can be achieved with the provided DC semiconductor relay.

[0031]

According to the first aspect of the present invention, when a current exceeding a predetermined current flows through the overcurrent detection resistor, the voltage across the overcurrent detection resistor increases, and the voltage across the overcurrent detection resistor is increased. The connection circuit connected in parallel to the overcurrent detection resistor is connected to the base-emitter of the bipolar transistor with the potential difference for flowing the base current sufficient to flow the collector current by changing the emitter-collector state of the bipolar transistor to a low impedance state. A potential difference is generated by adding a potential difference for causing a current to flow in the forward direction of the diode, and the collector current of the bipolar transistor flows.
Thus, when the collector current of the bipolar transistor flows, the charge charged in the output MOSFET is discharged, and the drain current of the output MOSFET is suppressed to a predetermined current. At this time, since the overcurrent detection resistor generates heat, the diode that forms the connection circuit together with the base and emitter of the bipolar transistor also generates heat, and the potential difference for flowing the current in the forward direction of the diode decreases. The voltage across the resistor for use also decreases, and in conjunction with the decrease in the voltage across the resistor for overcurrent detection, the drain current becomes smaller than a predetermined current, so that the output MOSFET is not damaged.

According to a second aspect of the present invention, in addition to the effect of the first aspect, the diode has a cathode connected to the base of the bipolar transistor and an anode connected to the emitter of the bipolar transistor. Since it is not connected to form an electric path through which the collector current of the bipolar transistor flows, it does not affect the flow of the collector current and does not affect the discharge of the charge between the gate and the source of the output MOSFET. .

According to the third aspect of the present invention, since the diode has the overcurrent detecting resistor provided on the silicon single crystal region provided thereon, the heat of the overcurrent detecting resistor generated by energization is reduced. This facilitates conduction and decreases the second potential difference for flowing a current in the forward direction of the diode, so that the drain current tends to decrease and the output MOSFE
The effect of the invention described in claim 1 that T is hardly damaged is easily exerted.

According to a fourth aspect of the present invention, since the overcurrent detecting resistor is not a diffusion resistor whose resistance decreases as the temperature rises, but is made of polysilicon whose resistance increases as the temperature rises, the resistance value increases when current is applied. The voltage at both ends decreases, and in conjunction with the decrease of the voltage at both ends, the drain current is easily reduced, and the output MOSFET is less likely to be damaged, so that the effect of the invention according to claim 1 is easily exerted.

[Brief description of the drawings]

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

FIG. 2 is a layout diagram of each element on a dielectric isolation substrate of the above.

FIG. 3 is a sectional view of the dielectric isolation substrate of the above.

FIG. 4 is a circuit diagram of a conventional example.

[Explanation of symbols]

 1 light emitting diode (light emitting element) 2 light receiving element (photodiode array) 3 output MOSFET 4 NPN bipolar transistor 5 overcurrent detection resistor 6 temperature detection diode 7 control MOSFET (control transistor) 30 connection circuit 40 control means

Claims (4)

[Claims] A light emitting element that emits light in response to an input signal;
A light-receiving element that receives light from the light-emitting element to generate photovoltaic power; and a photo-electromotive force generated by the light-receiving element is applied to charge the electric charge. Output MOSFET that changes from high impedance state to low impedance state between sources
A control means connected between the gate and the source of the output MOSFET for controlling charge and discharge of the electric charge in the output MOSFET, the control means including a control transistor for changing the impedance state in accordance with the generation and disappearance of the photoelectromotive force by the light receiving element; , An overcurrent detection resistor connected to the source of the output MOSFET, a bipolar transistor whose collector is connected to the gate of the output MOSFET, and a connection circuit connected in parallel to the overcurrent detection resistor. A semiconductor relay, comprising: a diode formed along with the diode. 2. The semiconductor relay according to claim 1, wherein said diode has a cathode connected to a base of said bipolar transistor to form said connection circuit together with said bipolar transistor. 3. The overcurrent detection resistor and the diode are both provided on a silicon single crystal region of a silicon substrate, and the overcurrent detection resistor and the diode are provided on the same silicon single crystal region. The semiconductor relay according to claim 1, wherein the diode is provided. 4. The semiconductor relay according to claim 1, wherein said overcurrent detecting resistor is made of polysilicon.