JP2001345685A - Semiconductor device and semiconductor relay - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device hard to break when an overvoltage is applied continuously. SOLUTION: The semiconductor device includes an output transistor 1, a detecting transistor 3 connected in parallel with the output transistor 1 and having a control terminal in which an input necessary for making continuity between the output terminals connected in parallel with the output transistor 1, a detecting impedance element 5 connected in series with the detecting transistor 3, and a control transistor 6 for closing or opening the individual output terminals of both the output transistor 1 and the detecting transistor 3 under control on the basis of a voltage across both sides of the detecting impedance element 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a semiconductor device having an overcurrent / overvoltage protection function and a semiconductor relay having the same.

[0002]

2. Description of the Related Art Conventionally, as a semiconductor device of this kind, FIG.
There are the following. This is an output transistor,
An overcurrent detection resistor and a control transistor are provided.

The output MOSFET 101 is of an enhancement type, and its source has an overcurrent detection resistor 102.
Is connected. The control transistor 103 is a bipolar transistor whose collector is an output MOS
The FET 101 is connected to the gate, and the base and the emitter are connected by an overcurrent detection resistor 102.

Next, the operation will be described. For example, the photoelectromotive force generated by a light receiving element (not shown) that has received an optical signal is
When the voltage is applied between the gate and the source of the output MOSFET 101, the output MOSFET 1
No. 01 is charged between the gate and the source, and conducts between the drain and the source. Here, when the photovoltaic power is no longer applied, the output MOSFET 101 is discharged from the charge charged between its gate and source, and cuts off between the drain and source.

When an overcurrent flows between the drain and the source of the output MOSFET 101, the voltage across the overcurrent detection resistor 102 increases, and the increased voltage becomes the base voltage. Control transistor 1
03 conducts between the collector and the emitter. Then, the electric charge charged between the gate and the source of the output MOSFET 101 is discharged through the collector and the emitter of the control transistor 103, the current flowing between the drain and the source is suppressed, and the destruction due to the overcurrent is prevented. You.

[0006]

In the conventional semiconductor device described above, when an overcurrent flows between the drain and the source of the output MOSFET 101, the output MOSFET
Although the current flowing between the drain and the source of the ET101 is suppressed, and the destruction of the output MOSFET 101 due to the overcurrent is prevented, under the condition that the overvoltage is continuously applied, the suppressed current continues to flow. The output MOSFET 101 may generate heat and be destroyed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to provide a semiconductor device which is hardly damaged even when an overvoltage is continuously applied, and a semiconductor device having the same. is there.

[0008]

In order to solve the above-mentioned problems, a semiconductor device according to the first aspect of the present invention has an output transistor and a control which is connected in parallel to the output transistor and which is required to conduct between output terminals. A detection transistor whose input value to the terminal is smaller than the output transistor, a detection impedance element connected in series to the detection transistor, and a detection transistor based on the voltage across the detection impedance element. And a control transistor for controlling opening and closing between the output terminals.

According to a second aspect of the present invention, in the semiconductor device of the first aspect, the detection impedance element is connected in series to a voltage division impedance element.

According to a third aspect of the present invention, in the semiconductor device according to the first or second aspect, the impedance element for detection includes one or more diodes.

A semiconductor device according to a fourth aspect of the present invention is the semiconductor device according to any one of the first to third aspects, wherein the output transistor and the detection transistor are:
Both are MOSFETs whose control terminals are connected to the control transistor so that the gate charge is controlled to charge and discharge, and by providing a potential difference between the control terminals of the output transistor and the detection transistor, The detection transistor has a configuration in which the input value is smaller than that of the output transistor.

According to a fifth aspect of the present invention, there is provided the semiconductor device according to the fourth aspect, further comprising a potential difference impedance element for controlling the potential difference between control terminals of the output transistor and the detection transistor. It is configured to be connected by a current element.

According to a sixth aspect of the present invention, in the semiconductor device according to the fifth aspect, the constant current element is a MOSFET for a constant current element and the potential difference connected between a gate and a source of the MOSFET for the constant current element. The configuration is made up of impedance elements.

According to a seventh aspect of the present invention, there is provided a semiconductor relay for emitting a light signal in response to an input signal, a light receiving element for generating a photoelectromotive force based on the light signal of the light emitting element, 7. The semiconductor device according to claim 1, wherein the semiconductor device according to claim 1 is connected to respective control terminals of the output transistor and the detection transistor such that an input for conducting between the output terminals is input. Configuration.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor device according to a first embodiment of the present invention will be described below with reference to FIG.

Reference numeral 1 denotes an output MOSFET (output transistor), which is in an enhancement mode, and whose drain (one output terminal) is connected to the output terminal 1 of the semiconductor device 10.
0a, and the source (the other output terminal) is connected to the output terminal 10b and the input terminal 10c of the semiconductor device 10.
And a gate (control terminal) is connected to an input terminal 10d of the semiconductor device 10 and a gate (control terminal) of a detection MOSFET 3 to be described later by a potential difference resistor (potential difference impedance) 2.

Reference numeral 3 denotes a detection MOSFET (detection transistor) in an enhancement mode in which the drain (one output terminal) is connected to the drain of the output MOSFET 1 and the source (the other output terminal) is connected to a voltage dividing resistor. It is connected in parallel to the output MOSFET 1 by being connected to the source of the output MOSFET 1 via a series circuit including a (voltage division impedance element) 4 and a detection resistor (detection impedance element) 5. The gate of the detection MOSFET 3 is connected to the input terminal 10 d of the semiconductor device 10, and the gate is connected to the potential difference resistor 2 as described above.
It is connected to the gate of the output MOSFET 1.

Since the gate of the detection MOSFET 3 is connected to the gate of the output MOSFET 1 by the potential difference resistor 2, an output corresponding to the potential difference between both ends of the potential difference resistor 2 will be described later in detail. MOS for
The potential of the gate is higher than that of the FET1, and the input value to the gate required to make the drain-source conductive, that is, the gate charge required to increase the gate potential is smaller than that of the output MOSFET 1. .

Reference numeral 6 denotes a control MOSFET (control transistor), which is in an enhancement mode. The drain of the control MOSFET is connected to the gate of the output MOSFET 1 and the detection MOSFET 3 is connected via the potential difference resistor 2.
And the source is connected to the source of the output MOSFET 1.

The control MOSFET 6 has the detection resistor 5 and the Zener diode 7 connected between its gate and source. Therefore, the potential difference between the gate and the source of the control MOSFET 6 does not exceed the Zener voltage of the Zener diode 7 and does not exceed the breakdown voltage of the gate oxide film even if the potential difference between both ends of the detection resistor 5 becomes large.

Next, the operation of the semiconductor device 10 will be described. For example, when a potential difference is input between the input terminals 10c and 10d based on an electromotive force generated by a photodiode array (not shown), both the output MOSFET 1 and the detection MOSFET 3 , And the drain and source respectively conduct. At this time, a current flows between the drain and the source of the detection MOSFET 3, so that the output terminals 10 a and 10 b
The voltage between them is divided by the on-resistance of the detection MOSFET 3, the voltage dividing resistance 4 and the detection resistance 5.

Here, for example, when an overcurrent flows or a load short circuit occurs, the protection operation starts. That is,
If an overcurrent flows or a load short circuit occurs, the output terminal 1
As described above, when the potential difference between the output terminals 10a and 10b increases, the voltage between the output terminals 10a and 10b becomes
Since the voltage is divided by the on-resistance of the FET 3, the voltage dividing resistor 4 and the detecting resistor 5, the potential difference between both ends of the detecting resistor 5 is also increased.

Then, the control MOSFET 6 whose gate and source are connected to both ends of the detection resistor 5 becomes conductive, thereby discharging the charge (gate charge) charged between the gate and source of the output MOSFET 1. ,
The charge (gate charge) charged between the gate and source of the detection MOSFET 3 is also discharged through the potential difference resistor 2. Therefore, the output MOSFET 1 and the detection MO
In the SFET 3, the state between the drain and the source shifts to the cutoff state.

As described above, in the semiconductor device 10, the control MOSFET 6 includes the output MOSFET 1 and the output MOSFET 1 based on the potential difference between both ends of the detection resistor 5.
The switching between the drain and the source of the detection MOSFET 3 connected in parallel to 1 is controlled.

When a potential difference is input between the input terminals 10c and 10d based on the electromotive force generated by the photodiode array, generally, the input terminals 10c and 10d
Since the potential difference inputted between d and d is smaller than that at the beginning of the input, the on-resistance of the detection MOSFET 3 increases, the current flowing between the drain and source of the detection MOSFET 3 decreases, and the voltage difference between both ends of the detection resistor 5 decreases. Is the control MOS
It is stabilized in a state where it matches the threshold value of the FET 6.

In order to maintain this state, the input terminal 1
Since the potential difference input between 0c and 10d may be smaller than before the start of the protection operation, the charge supplied from the input terminal 10d flows through the potential difference resistor 2 and corresponds to a voltage drop due to the potential difference resistor 2. MO for output
The potential of the gate of the SFET 1 becomes smaller than the potential of the input terminal 10d, that is, the gate potential of the detection MOSFET 3, and the gate-source voltage of the output MOSFET 1 is determined.

Therefore, the output MOSFET 1 always corresponds to the voltage between both ends of the potential difference resistor 2,
Since the voltage between the gate and the source is smaller than that of the FET 3, the voltage becomes closer to the cutoff state than the MOSFET 3 for detection.

Therefore, as a whole of the semiconductor device 10,
The current flowing between the output terminals 10a and 10b is
Only a small current flows between the drain and source of the SFET 3, and the substantially cutoff state continues.

On the other hand, in a normal state, the input terminals 10c, 1
When the potential difference is no longer input between 0d and 0d, the output MOSF
The charge charged between the gate and the source of the ET1 and the detection MOSFET 3 is discharged through the control MOSFET 6, and the drain and the source of the output MOSFET 1 and the detection MOSFET 3 gradually approach the cutoff state. When the on-resistance increases and the potential difference between the output terminals 10a and 10b exceeds a predetermined potential difference, the above-described protection operation is performed and the connection between the output terminals 10a and 10b is rapidly performed as in the case where an overvoltage occurs. It becomes a cutoff state.

Next, the semiconductor relay 20 to which the semiconductor device 10 is connected will be described with reference to FIG. The semiconductor relay 20 includes a light emitting diode (light emitting element) 21, a photodiode array (light receiving element) 22, a charge / discharge control MOSFET in addition to the semiconductor device 10.
23, a charge / discharge control resistor 24.

The light emitting diode 21 has an input terminal 20a,
An optical signal is emitted according to an input signal input during 20b. The photodiode array 22 includes a plurality of photodiodes 22a connected in series, receives a light signal from the light emitting diode 21, and generates a photoelectromotive force. The charge / discharge control MOSFET 23 is in a depletion mode. The drain is connected to the drain of the photodiode array 22, and the source is connected to one end of the charge / discharge control resistor 24, thereby being connected to the cathode of the photodiode array 22 via the charge / discharge control resistor 24. ing. The charge / discharge control M
The OSFET 23 has a gate connected to a charge / discharge control resistor 24.
Of the charge / discharge control resistor 24
Are connected between the gate and the source.

For each of the above-described elements, the present semiconductor device 1
0 is connected as shown below. That is, the anode of the photodiode array 22 and the charge / discharge control MO
The drain of the SFET 23 is connected to the gate of the output MOSFET 1 via the potential difference resistor 2,
The gate of the detection MOSFET 3 is connected.

An output MO is connected between the source of the charge / discharge control MOSFET 23 and one end of the charge / discharge control resistor 24.
The source of SFET1 is connected and the detection MO
The source of the SFET 3 is connected via the voltage dividing resistor 4 and the detecting resistor 5, and further connected to the anode of the Zener diode 7 and the source of the control MOSFET 6.

Next, the operation of the semiconductor relay 20 will be described. When an input signal is input between both input terminals 20a and 20b, the light emitting diode 21 emits an optical signal. This optical signal is received by the photodiode array 22.
The photodiode array 22 generates a photoelectromotive force by receiving an optical signal emitted by the light emitting diode 21. This photovoltaic voltage is applied between the respective gates and sources of the output MOSFET 1 and the detection MOSFET 3, and the output MOSFET 1 and the detection MOSFET 3
Are charged between the gate and the source of the IGBT.

The output MOSFET 1 and the detection MOSFET are based on the photovoltaic power generated by the photodiode array 22.
The current for charging between the gate and source of each FET 3 flows between the drain and source of the charge / discharge control MOSFET 23 via the control resistor 24.

Then, a voltage is generated between both ends of the charge / discharge control resistor 24, so that the charge / discharge control MOSFET 23
In this case, the gate has a negative bias voltage with respect to the source, and the state between the drain and source changes from a conductive state to a cutoff state. As a result, the respective gates and sources of the output MOSFET 1 and the detection MOSFET 3 are efficiently charged, and the output MOSFET 1 and the detection MOSFET
ET3 conducts.

If no input signal is input between the two input terminals 20a and 20b, the light emitting diode 21 does not emit a light signal, and the photodiode array 22 does not generate photovoltaic power. Current
The bias voltage that has stopped flowing between the drain and source of the charge / discharge control MOSFET 23 is no longer flowing to the charge / discharge control resistor 24, so that the charge / discharge control MOS
The conduction between the drain and source of the FET 23 is restored.

As a result, the electric charge charged between the gate and the source of the output MOSFET 1 is discharged through the potential difference resistor 2 and the drain and the source of the control MOSFET 6, so that the drain and the source are returned to the cutoff state. I do. In addition, since the charge charged between the gate and the source of the detection MOSFET 3 is discharged through the drain and the source of the control MOSFET 6, the state between the drain and the source is returned to the cutoff state.

On the other hand, in the normal state, the output terminals 10a, 1
When an overcurrent flows or a load short circuit occurs during the period 0b, the above-described protection operation by the semiconductor device 10
The current flowing between the output terminals 10a and 10b is
Only a small current flows between the drain and source of the SFET 3, and the substantially cutoff state continues.

In such a semiconductor device, the control MO
When the SFET 6 controls opening and closing between the drain and source of the output MOSFET 1 and the detection MOSFET 3 connected in parallel to the output MOSFET 1 based on the voltage between both ends of the detection resistor 5, the SFET 6 conducts between the drain and source. Input to the gate required for the operation, that is, the detection MO in which the gate charge is smaller than the output MOSFET 1
By making only the SFET 3 slightly conductive and in a substantially cut-off state, even if overvoltage is continuously applied, the output MO
SFET 1 is less likely to be destroyed.

Since the detection resistor 5 is connected in series with the voltage dividing resistor 4, the voltage applied to the detecting resistor 5 becomes a voltage divided by the voltage dividing resistor 4. By appropriately setting the resistance value of the resistance 4, the detection resistance 5
Can be set to a desired voltage.

The output MOSFET 1 and the detection M
By providing a potential difference between the respective gates of the OSFET 3, the detection MOSFET 3 outputs the input value to the gate necessary for conducting between the drain and source to the output M.
Since the output MOSFET is smaller than the OSFET 1, the output MOS is set so that the input value to the gate required for conducting between the drain and the source is smaller than the output MOSFET 1.
The fabrication becomes easier as compared with the case where the thresholds of the FET 1 and the detection MOSFET 3 are different.

In the above-described semiconductor relay,
The semiconductor device 10 is connected so that an input for conducting between the drain and the source is input to each gate of the output MOSFET 1 and the detection MOSFET 3 based on the electromotive force of the photodiode array 22.
The effects of the present semiconductor device 10 can be obtained.

Next, a semiconductor device according to a second embodiment of the present invention will be described below with reference to FIG. Elements that are substantially the same as those of the semiconductor device of the first embodiment are denoted by the same reference numerals, and only those parts that are different from the first embodiment are described. In the semiconductor device of the first embodiment, the detection impedance element is the detection resistor 5, whereas the present embodiment has a configuration including a plurality of diodes 5a connected in series along the forward direction. , The cathode is connected to the source of the control MOSFET 6 and the anode is connected to the control MOSFET 6.
It is connected to the gate of ET6.

The semiconductor device of the present embodiment is connected in the same manner as the semiconductor device of the first embodiment, so that a semiconductor relay 20 is formed.

In this semiconductor device, in addition to the effects of the semiconductor device of the first embodiment, a plurality of diodes 5a, whose detection forward elements are elements whose forward voltage is grasped in advance, are connected in series. Therefore, the voltage applied to the detection impedance element can be easily set to a desired voltage.

In the present embodiment, the detecting impedance element includes a plurality of diodes 5a connected in series, but may include a single diode 5a.

Next, a third embodiment of the semiconductor device of the present invention will be described below with reference to FIG. Elements that are substantially the same as those of the semiconductor device of the first embodiment are denoted by the same reference numerals, and only those parts that are different from the first embodiment are described. In the semiconductor device of the first embodiment, each gate of the output MOSFET 1 and the detection MOSFET 3 is connected to the potential difference resistor 2.
In the semiconductor device of this embodiment, the output MOSFET 1 and the detection MOSFET 3
Are connected by a constant current element 8 including a potential difference resistor 2. More specifically, the constant current element 8 includes a MOSFET 9 for a constant current element and a potential difference resistor 2 connected between the gate and the source of the MOSFET 9 for the constant current element.

The semiconductor device of the present embodiment is connected in the same manner as the semiconductor device of the first embodiment, whereby a semiconductor relay 20 is formed.

In this semiconductor device, in addition to the effects of the semiconductor device of the first embodiment, the output MOSFET 1
And the gate of the detection MOSFET 3 is connected by the constant current element 8 including the potential difference resistor 2, so that when the gate charge is discharged during the protection operation,
A constant current flows through the potential difference resistor 2 irrespective of the potential difference between the two gates, and the output MOSFET 1 is controlled by the output MOSFET 1 regardless of the discharge state of the gate charge of the detection MOSFET 3.
The gate charge can be discharged. Therefore, output M
The OSFET 1 does not need to wait for the detection MOSFET 3 to discharge before discharging.
Since the time required for the discharge can be shortened, the output MOSFET 1 can be cut off at a high speed, and the protection operation of preventing the output MOSFET 1 from being broken can be performed at a high speed.

The constant current element 8 is an MO for the constant current element.
Since it is composed of the SFET 9 and the potential difference resistor 2 connected between the gate and the source of the MOSFET 9 for the constant current element,
The configuration of the constant current element 8 can be simplified.

In the semiconductor device of the present embodiment, the detection impedance element is constituted by the detection resistor 5, but, similarly to the semiconductor device of the second embodiment, a plurality of serially connected in series in the forward direction. In this case, the voltage applied to the detection impedance element can be easily set to a desired voltage, similarly to the semiconductor device of the second embodiment.

Further, in the semiconductor devices of the first to third embodiments, the input value to the gate required for conducting between the drain and the source is determined by the potential difference between the gates of the output MOSFET 1 and the detection MOSFET 3. Is provided, the detection M is higher than the output MOSFET 1.
Although the OSFET 3 is made smaller, for example, by changing the threshold value, the detection MO
The SFET 3 may be made smaller.

[0054]

According to the semiconductor device of the present invention, the control transistor is configured to output the output transistor and the output of the detection transistor connected in parallel to the output transistor based on the voltage between both ends of the detection impedance element. When the switching between the terminals is controlled, by appropriately setting only the detection transistor whose input value to the control terminal necessary for conducting between the output terminals is smaller than the output transistor is set to be slightly conducting, the overvoltage is reduced. Even when the voltage is continuously applied, the output transistor is hardly damaged.

According to a second aspect of the present invention, in addition to the effect of the first aspect, the detection impedance element is applied to the detection impedance element by being connected in series with the voltage division impedance element. The voltage applied to the detection impedance element can be set to a desired voltage by appropriately setting the impedance of the voltage division impedance element because the divided voltage is a divided voltage with the voltage division impedance element.

According to a third aspect of the present invention, in addition to the effect of the semiconductor device according to the first or second aspect, in addition to the effect of the first or second aspect, the detecting impedance element is an element whose forward voltage is grasped in advance. Since one or more diodes are used, the voltage applied to the detection impedance element can be easily set to a desired voltage.

According to a fourth aspect of the present invention, in addition to the effects of the semiconductor device of the first aspect, a potential difference is provided between the control terminals of the output transistor and the detection transistor. This allows the detection transistor to have a smaller input value to the control terminal for conducting between the output terminals than the output transistor. The manufacturing becomes easier as compared with the case where the respective thresholds of the output transistor and the detection transistor are different so that the input value is smaller than that of the output transistor.

According to a fifth aspect of the present invention, in addition to the effects of the semiconductor device of the fourth aspect, a constant current element including a potential difference impedance element is provided between the control terminals of the output transistor and the detection transistor. When the gate charge is discharged, a constant current flows through the potential difference impedance element regardless of the potential difference between the control terminals when the gate charge is discharged, and the MOSFET serving as the output transistor is connected to the detection transistor. Eggplant MOSFE
The gate charge can be discharged regardless of the discharge state of the gate charge of T. Therefore, the MOSFET forming the output transistor is replaced by the MOSF forming the detection transistor.
It is not necessary to wait for the discharge of the ET before discharging, and the time required for the discharge can be shortened. The protection operation of destruction prevention is performed at high speed.

According to a sixth aspect of the present invention, in addition to the effect of the semiconductor device of the fifth aspect, the constant current element includes a MOSFET for a constant current element and a MOSFET for the constant current element.
, The configuration of the constant current element can be simplified.

According to a seventh aspect of the present invention, based on the electromotive force of the light receiving element, the control terminal of each of the output transistor and the detection transistor receives an input for conducting between the output terminals. Since the semiconductor device according to any one of claims 1 to 6 is connected, the effect of the semiconductor device according to any one of claims 1 to 6 can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a semiconductor relay having the same.

FIG. 3 is a circuit diagram of a second embodiment of the semiconductor device of the present invention.

FIG. 4 is a circuit diagram of a third embodiment of the semiconductor device of the present invention.

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

[Explanation of symbols]

 Reference Signs List 1 output MOSFET (output transistor) 2 potential difference impedance element (potential difference resistor) 3 detection MOSFET (detection transistor) 4 voltage division resistance (voltage division impedance element) 5 detection resistance (detection impedance element) 5a diode Reference Signs List 6 control MOSFET (control transistor) 7 constant current element 8 constant current element MOSFET 10 semiconductor device 20 semiconductor relay 21 light emitting diode (light emitting element) 22 photodiode array (light receiving element)

Continued on the front page F term (reference)

Claims (7)

[Claims] 1. An output transistor, a detection transistor connected in parallel to the output transistor and having a smaller input value to a control terminal required for conducting between output terminals than an output transistor, and connected in series to the detection transistor And a control transistor for controlling opening and closing between output terminals of the output transistor and the detection transistor based on a voltage between both ends of the detection impedance element. . 2. The semiconductor device according to claim 1, wherein said impedance element for detection is connected in series to an impedance element for voltage division. 3. The semiconductor device according to claim 1, wherein the impedance element for detection includes one or more diodes. 4. The output transistor and the detection transistor are MOSFETs each having a control terminal connected to the control transistor so that charging and discharging of gate charge are controlled. 4. The semiconductor device according to claim 1, wherein the detection transistor has a smaller input value than the output transistor by providing a potential difference between respective control terminals of the output transistor. 5. 5. The semiconductor device according to claim 4, wherein control terminals of said output transistor and said detection transistor are connected by a constant current element including a potential difference impedance element for said potential difference. 6. The constant current element is a constant current element MOS.
6. The semiconductor device according to claim 5, comprising an FET and the potential difference impedance element connected between the gate and the source of the constant current element MOSFET. 7. A light emitting element that emits an optical signal in response to an input signal, a light receiving element that generates a photoelectromotive force based on the optical signal of the light emitting element, an output transistor based on the electromotive force of the light receiving element, and a detection circuit. 7. The semiconductor device according to claim 1, wherein the semiconductor device according to any one of claims 1 to 6, wherein the semiconductor device according to any one of claims 1 to 6 is connected to each control terminal of the transistor for input so that an input for conducting between output terminals is provided. relay.