JP2001028437A - Overcurrent protective device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overcurrent protective device structure, which is reduced in cost and equipped with a PTC(positive temperature coefficient) thermistor, that is operates on a low rated voltage and is small in size. SOLUTION: An overcurrent protective device used for a MOSFET 101 is equipped with a PTC thermistor 104, disposed between the source electrode 102 and source terminal 103 of the MOSFET 101 and a bipolar transistor 106, which is connected between the gate electrode 105 and the source terminal 103 for reducing the gate voltage of the MOSFET 101 due to a rise in a potential difference across the thermistor 104.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection device for limiting an overcurrent when an abnormality such as a load short circuit occurs.

[0002]

2. Description of the Related Art FIG. 6 shows a circuit of a conventional overcurrent protection device using a PTC thermistor. In the circuit shown in FIG.
One end of a PTC thermistor is connected to the drain of the SFET, and a load and a load power supply are connected in series between the source of the MOSFET and the other end of the PTC thermistor. Also,
A signal source of a gate signal for driving the MOSFET is connected between the gate and the source of the MOSFET. The positive temperature coefficient thermistor used in the circuit of FIG. 6 has characteristics as shown in FIG. In the graph of FIG. 7, the horizontal axis represents the temperature of the positive temperature coefficient thermistor, and the vertical axis represents the resistance value of the positive temperature coefficient thermistor. As shown in FIG. 7, the positive temperature coefficient thermistor is an element having a property that its resistance value rapidly increases when its temperature exceeds a predetermined temperature.

In the circuit shown in FIG. 6, when a load short circuit occurs, an overcurrent flows through the PTC thermistor and the MOSFET, and the temperature of the PTC thermistor rises due to self-heating of the PTC thermistor, thereby increasing the resistance value. As a result, the current flowing through the PTC thermistor and the MOSFET decreases, and the voltage applied to the PTC thermistor and the current flowing through the circuit cause the PTC thermistor to self-heat, so that the current flowing through the circuit remains low. Circuit destruction due to current can be prevented.

Further, another example of the overcurrent protection device will be described with reference to FIG. The circuit illustrated in FIG. 8 includes a light-emitting element that generates an optical signal based on an electric signal input to an input unit,
An overcurrent detection resistor (detection resistor) is provided for a circuit including a light receiving element array that receives an optical signal of a light emitting element and generates an electric signal, and a MOSFET that is driven by a signal output from the light receiving element array. It incorporates an overcurrent protection circuit including a latch circuit. In the circuit shown in FIG. 8, a thyristor is used to configure the latch circuit. The overcurrent detection resistor (detection resistor) consists of a light receiving element and a MOSFE
The anode, cathode, and gate of the thyristor are inserted between the sources of T, and are connected to the gate of the MOSFET, the connection point between the light receiving element and the detection resistor, and the connection point between the source of the MOSFET and the detection resistor, respectively.

When a short circuit occurs in the circuit shown in FIG. 8, an overcurrent flows through the detection resistor, the latch circuit operates, the thyristor is turned on, and the gate potential of the MOSFET becomes substantially equal to the source potential. When the current flowing through the circuit decreases, the voltage across the sensing resistor also decreases.
Since the gate and the source of T are substantially short-circuited by the latch circuit, the MOSFET is kept in the cut-off state, and the circuit is prevented from being damaged by an overcurrent.

[0006]

However, in the configuration shown in FIG. 6, since a load current flows through the PTC thermistor when the load is short-circuited, it is necessary to use a PTC thermistor having a rated voltage higher than the load voltage of the load power supply. is there. The higher the rated voltage, the larger the size of the positive temperature coefficient thermistor and the higher the cost.

In the configuration shown in FIG. 8, since the latch circuit is connected between the gate and the source of the MOSFET, it is necessary to supply a current to the latch circuit.
It is necessary to increase the gate current for driving the OSFET. In order to increase the gate current, it is necessary to increase the area of the light receiving element array, and there is a problem that the cost increases.

Further, since the current limiting action of the positive temperature coefficient thermistor is generally caused by an increase in resistance value due to self-heating of the thermistor, the operating speed of the current limiting is limited to an overcurrent protection device composed of only semiconductor elements. Therefore, there is a risk that the MOSFET may be destroyed earlier than the current limit operation speed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to use a positive characteristic thermistor having a low rated voltage and a small shape.
An object of the present invention is to provide a structure of an overcurrent protection device capable of reducing costs.

[0010]

The overcurrent protection device according to the present invention is used for an insulated gate semiconductor device in which a drain electrode can be turned on and off by a gate electrode formed through a gate oxide film. An overcurrent protection device, wherein the PTC thermistor is disposed between a source electrode and a source terminal of the insulated gate semiconductor device; and the PTC thermistor is connected between the gate electrode and the source terminal of the insulated gate semiconductor device. And a driving element for lowering the gate voltage of the insulated gate semiconductor device by increasing the voltage between both ends. With this configuration, it is possible to use a PTC thermistor having a low rated voltage regardless of the load voltage of the circuit.
The latch function can be realized without increasing the gate current of the OSFET.

Further, the overcurrent protection device according to claim 2 is
A light-emitting element that generates an optical signal based on an electric signal from the input unit; and a light-receiving element array that receives the optical signal of the light-emitting element and generates an electric signal, and is driven by the electric signal from the light-receiving element array. An overcurrent protection device used for an insulated gate semiconductor device, wherein a positive temperature coefficient thermistor disposed between a source electrode and a source terminal of the insulated gate semiconductor device, and between a gate electrode and a source terminal of the insulated gate semiconductor device. A driving element connected to the gate of the insulated gate semiconductor device, the drive element being connected to the gate of the insulated gate semiconductor device by increasing the voltage across the positive temperature coefficient thermistor.

The overcurrent protection device according to claim 3 is
A light-emitting element that generates an optical signal based on an electric signal from the input unit; and a light-receiving element array that receives the optical signal of the light-emitting element and generates an electric signal, and is driven by the electric signal from the light-receiving element array. An overcurrent protection device used for first and second insulated gate semiconductor devices for output, wherein a source electrode of the first insulated gate semiconductor device for output is connected to the second output via a positive temperature coefficient thermistor. The source electrodes of the output insulated gate semiconductor device are connected to each other and are connected between the gate electrode of the first output insulated gate semiconductor device and the source electrode of the second output insulated gate semiconductor device. A first drive element for lowering a gate voltage of the first output insulated gate semiconductor device by an increase in a voltage between both ends of the PTC thermistor; and a second output insulated gate. The gate of the second output insulated gate semiconductor device is connected between the gate electrode of the semiconductor device and the source electrode of the first output insulated gate semiconductor device. A second driving element for lowering a voltage; and a series circuit for voltage division composed of a plurality of high resistances connected in parallel with the positive temperature coefficient thermistor. It is characterized in that it is connected to a predetermined voltage dividing point of the voltage series circuit.

Further, the overcurrent protection device according to claim 4 is
2. The overcurrent protection device according to claim 1, wherein the PTC thermistor is thermally coupled to the insulated gate semiconductor device. As described above, by thermally coupling the positive temperature coefficient thermistor to the MOSFET, the temperature of the positive temperature coefficient thermistor can be raised by utilizing not only the self-heating of the positive temperature coefficient thermistor but also the heat generation of the MOSFET. The resistance value rising speed can be accelerated, and a quick current interruption operation can be realized.

The overcurrent protection device according to claim 5 is
2. The overcurrent protection device according to claim 1, wherein the driving element is thermally coupled to the insulated gate semiconductor device.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an overcurrent protection device according to the present invention will be described with reference to FIG. The circuit shown in FIG. 1 includes a MOSFET 101 whose drain and source can be turned on and off by a voltage applied to a gate electrode formed through a gate oxide film, and a gate signal connected between the gate and the source of the MOSFET 101. Generator 10
7 and a circuit including a series circuit of a load 108 and a load power supply 109 connected between the drain and the source of the MOSFET 101.
3, a positive temperature coefficient thermistor 104 connected between
An overcurrent protection device, which is connected between the gate electrode 105 and the source terminal 103 of the ET 101 and includes a drive element (bipolar transistor 106) that lowers the gate voltage of the MOSFET 101 by increasing the voltage across the positive temperature coefficient thermistor 104, is added. It was done.

The emitter, collector and base of the bipolar transistor 106 are respectively connected to the connection point between the gate signal generator 107 and the source terminal 103 and the gate electrode 1
05, connected to the source electrode 102.

In the circuit shown in FIG.
07 receives a gate signal, the MOSFET 10
1 is turned on, and a current flows through a series circuit (circuit 110) of the MOSFET 101, the positive temperature coefficient thermistor 104, the load 108, and the load power supply 109. Here, the resistance value of the load 108 is 5000Ω, and the drain
When the resistance between the sources is 20Ω and the resistance of the positive temperature coefficient thermistor 104 is 1Ω, the current flowing through the circuit 110 is
It is approximately 0.1A. Here, when the load 108 is short-circuited, a current of about 25 A flows through the circuit without the overcurrent protection circuit, and the MOSFET 101 is destroyed.

However, when the load 108 is short-circuited and an overcurrent starts to flow, the positive temperature coefficient thermistor 104 self-heats, and its resistance increases by about three digits, and the resistance value of the positive temperature coefficient thermistor 104 increases to about 1000Ω. . As a result, when the voltage between both ends of the positive temperature coefficient thermistor 104 rises to about 0.6 V, the base-emitter of the bipolar transistor 106 is forward-biased, and the bipolar transistor 106
Becomes conductive, and lowers the gate voltage of MOSFET 101. When the voltage between both ends of the positive characteristic thermistor 104 is 0.
When the voltage is about 6 V, the load current value is about 0.6 mA, and the MOSFET 401 is not destroyed. In addition, since the voltage across the positive temperature coefficient thermistor 104 does not exceed about 0.6 V, which is the forward voltage between the base and the emitter of the bipolar transistor 106, the voltage does not depend on the value of the load voltage. A voltage of about 5 V can be used.

A different embodiment of the overcurrent protection device of the present invention will be described with reference to FIG. The circuit shown in FIG.
A light-emitting element 211 that generates an optical signal by an electric signal input from the input unit, and receives an optical signal of the light-emitting element 211,
A light receiving element array 212 for generating an electric signal, and a MO driven by the electric signal output from the light receiving element array 212
For a circuit including an SFET 201 and a series circuit of a load 208 and a load power supply 209 connected between the drain and source of the MOSFET 201, a positive temperature coefficient thermistor 204 connected between the source electrode 202 and the source terminal 203
And a driving element (bipolar transistor 206) connected between the gate electrode 205 and the source terminal 203 of the MOSFET 201 to decrease the gate voltage of the MOSFET 201 by increasing the voltage across the positive temperature coefficient thermistor 204.
And an overcurrent protection device comprising:

The operation of the circuit shown in FIG.
This is the same as the operation of the circuit shown in FIG. Since the positive temperature coefficient thermistor 204 keeps maintaining a high resistance value due to self-heating, as shown in the circuit of FIG.
It is not necessary to connect a latch circuit to the gate terminal of the gate. Therefore, in the case of a circuit for driving a MOSFET with an electric signal generated by an optical signal as shown in FIG. 2, it is not necessary to increase the light receiving element array 212 to increase the gate current.

Another embodiment of the overcurrent protection device of the present invention will be described with reference to FIG. The circuit illustrated in FIG. 3 includes a light emitting element 311 that generates an optical signal based on an electric signal input from an input unit, a light receiving element array 312 that receives the optical signal of the light emitting element 311 and generates an electric signal,
A first output insulated gate semiconductor device (MOSFE) driven by an electric signal from the light receiving element array 312
T301A) and a second output insulated gate semiconductor device (MOSFET 301B) with an overcurrent protection circuit added.

In the circuit shown in FIG.
4 through the source electrode 302 of the MOSFET 301A.
A is connected to the source electrode 302B of the MOSFET 301B, and the gate electrode 305A of the MOSFET 301A is connected.
And the source electrode 302B of the MOSFET 301B.
The rise in the voltage across the positive temperature coefficient thermistor 304 causes the MO
A first driving element (bipolar transistor 306A) for reducing the gate voltage of SFET 301A is connected. Also, the gate electrode 302 of the MOSFET 301B
Between B and the source electrode 302A of the MOSFET 301A, the voltage between both ends of the positive temperature coefficient thermistor 304 increases.
A second drive element (bipolar transistor 306B) for reducing the gate voltage of MOSFET 301B is connected. Further, in parallel with the positive characteristic thermistor 304,
A series circuit (series circuit for voltage division) of a plurality of high resistances (high resistances 313A and 313B) is connected to the light receiving element array 312.
Is connected to a voltage dividing point (a connection point between the high resistance 313A and the high resistance 313B) of the voltage dividing series circuit.

The circuit shown in FIG.
MOSFET 301A and MOS through a 3B series circuit
The source terminals of the FET 301B are connected to each other, and the drain terminals of the FET 301B are connected to the output unit, so that the current can be controlled bidirectionally.

In a normal operation, if the resistance value of the positive characteristic thermistor 304 is 1Ω and the resistance values of the high resistances 313A and 313B are 500Ω respectively, the load current mainly flows through the positive characteristic thermistor 304. About 0.6A
In the state of about the value, the bipolar transistor 30
6A and 306B are in a non-operating state (OFF state).
When a load short circuit occurs, the resistance of the positive temperature coefficient thermistor 304 increases by about three digits due to self-heating and becomes about 1000Ω. At this time, equivalently, the high resistance 313A,
Since 313B is connected in parallel with the positive temperature coefficient thermistor 304, the combined resistance value is 500Ω. As a result, the voltage between the base and the emitter of the bipolar transistors 306A and 306B becomes about 0.6 V, and the MOSF
Gate electrode 305 of each of ET301A and 301B
A, 305B and the terminal on the low voltage side of the light receiving element array 312 are short-circuited via the high resistances 313A, 313B, so that the load current is limited to about 1.2 mA.

By configuring as shown in FIG. 3,
The overcurrent protection of the circuit that controls the current in both directions can be performed with one positive-characteristic thermistor that is a current limiting element. Since the high resistances 313A and 313B can be made extremely small by a normal semiconductor manufacturing technique, the use of the dielectric isolation substrate allows the light receiving element array 31 to be formed.
2. It can be formed on the same semiconductor substrate together with the bipolar transistors 313A and 313B.

Next, another embodiment of the overcurrent protection device will be described with reference to FIG. FIG. 4 shows a ceramic substrate 4
00 is a plan view of a circuit formed on the ceramic substrate 4.
00, a MOSFET 401 and a MOSFET 40
1, a positive temperature coefficient thermistor 404 disposed between the source electrode and the source terminal, and a bipolar transistor connected between the gate electrode and the source terminal of the MOSFET 401 and lowering the gate voltage of the MOSFET 401 by increasing the voltage across the positive temperature coefficient thermistor 404. 406 are formed.

In the structure shown in FIG. 4, the MOSFET 401 and the positive temperature coefficient thermistor 404 are arranged on the same ceramic substrate 400 and are thermally coupled.
Positive temperature coefficient thermistor 40 efficiently dissipates heat due to heat generated by 401
4, the PTC thermistor 404 is heated not only by the temperature rise due to the self-heating of the PTC thermistor 404 but also by the heat generated by the MOSET 401. Therefore, when an overcurrent flows, the resistance value of the positive temperature coefficient thermistor 404 can be increased earlier to limit the load current.

Referring to FIG. 5, another embodiment of the overcurrent protection device will be described. FIG. 5 is a cross-sectional view of the semiconductor chip 514. The semiconductor chip 514 has a MOSFET that can be turned on / off by a voltage input between the drain and the source.
501, a positive temperature coefficient thermistor 504 arranged between the source electrode 502 and the source terminal 503, and a MOSFET 50
1 is connected between the gate electrode 505 and the source terminal 503 of the positive characteristic thermistor 504.
A drive element (MOSFET 513) for lowering the gate voltage of the MOSFET 501 is formed.

In the structure shown in FIG. 5, a MOSFET 501 and a MOSFET 513 are formed on the same semiconductor chip 514 and are thermally coupled. The current required to turn on MOSFET 513 is MOSFET 513
When the temperature of the high
By thermally coupling T501 and MOSFET 513, when a load is short-circuited, heat generated by MOSFET 501 is efficiently transmitted to MOSFET 513, and MOSF
Since the ET 513 can be turned on earlier, a higher-speed overcurrent protection operation can be performed.

In the embodiment, the switching element (insulated gate type semiconductor device) of the load current is a MOSFET.
However, it may be an IGBT or the like.

[0031]

According to the overcurrent protection device of the present invention, a positive thermistor with a low rated voltage can be used as a current limiting element regardless of the load voltage of the circuit. As compared with the conventional method, an overcurrent protection device having a smaller shape and lower cost can be realized. Further, since the overcurrent protection operation is performed by utilizing the increase in the resistance value of the positive temperature coefficient thermistor due to the self-heating of the positive temperature coefficient thermistor, there is no need to newly provide a latch circuit at the gate terminal of the insulated gate semiconductor device. Since the latch function can be realized without increasing the gate current, the overcurrent protection device can be operated even with a small current generated from the light receiving element array, for example.

According to the overcurrent protection device of the third aspect,
With one positive temperature coefficient thermistor, which is a current limiting element, overcurrent protection of a circuit for controlling bidirectional current can be performed, and miniaturization and cost reduction can be achieved.

According to the overcurrent protection device of the fourth aspect,
By thermally coupling the PTC thermistor and the insulated gate semiconductor device, not only the self-heating of the PTC thermistor but also the heat generated by the insulated gate semiconductor device can be used to raise the temperature of the PTC thermistor. Since the rate of rise of the resistance value of the positive characteristic thermistor can be accelerated and a quick current interruption operation can be realized, the reliability of the overcurrent protection device can be improved.

According to the overcurrent protection device of the fifth aspect,
By thermally coupling the driving element and the insulated gate semiconductor device, the driving element can be turned on more quickly and a quick current interruption operation can be realized.
The reliability of the overcurrent protection device can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of an overcurrent protection device of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the overcurrent protection device of the present invention.

FIG. 3 is a circuit diagram showing still another embodiment of the overcurrent protection device of the present invention.

FIG. 4 is a plan view of a ceramic substrate on which a circuit of the overcurrent protection device of the present invention is formed.

FIG. 5 is a sectional view of a semiconductor chip on which a circuit of the overcurrent protection device of the present invention is formed.

FIG. 6 is a circuit diagram of a conventional overcurrent protection device.

FIG. 7 is a characteristic diagram of a positive temperature coefficient thermistor.

FIG. 8 is a circuit diagram of a conventional overcurrent protection device.

[Explanation of symbols]

101, 201 MOSFET (insulated gate type semiconductor device) 104, 204, 304 PTC thermistor 106, 206 Bipolar transistor (drive element) 211, 311 Light emitting element 212, 312 Light receiving element array 301A MOSFET (first output insulated gate type) Semiconductor device) 301B MOSFET (second output insulated gate semiconductor device) 306A Bipolar transistor (first drive element) 306B Bipolar transistor (second drive element) 313A, 313B High resistance 404, 504 Positive temperature coefficient thermistor 701 801 MOSFET (insulated gate semiconductor device)

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shigeo Akiyama 1048 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Works F-term (reference) 5F038 AV05 AV06 AV20 BB08 BH02 BH06 BH07 BH14 BH20 CA08 EZ20 5F040 DA25 DB01 DB07 DB10 EB12 EB14 EF18 5F048 AB10 AC04 AC07 BA01 BC03 CC01 CC08 CC10 CC17

Claims (5)

[Claims] An overcurrent protection device used in an insulated gate semiconductor device capable of turning on and off between a drain and a source by a gate electrode formed through a gate oxide film,
A positive temperature coefficient thermistor disposed between the source electrode and the source terminal of the insulated gate type semiconductor device, connected between the gate electrode and the source terminal of the insulated gate type semiconductor device, and an increase in the voltage across the positive temperature coefficient thermistor, A driving element for lowering a gate voltage of the insulated gate semiconductor device. 2. A light-emitting element for generating an optical signal in response to an electric signal from an input unit, and a light-receiving element array for receiving the optical signal of the light-emitting element and generating an electric signal. An overcurrent protection device used for an insulated gate semiconductor device driven by a signal, a positive temperature coefficient thermistor disposed between a source electrode and a source terminal of the insulated gate semiconductor device, and a gate electrode of the insulated gate semiconductor device A drive element connected between the PTC thermistor and a source terminal, the drive element decreasing the gate voltage of the insulated gate semiconductor device by increasing the voltage across the PTC thermistor. 3. A light-emitting element for generating an optical signal in response to an electric signal from an input unit, and a light-receiving element array for generating an electric signal in response to the light signal of the light-emitting element. An overcurrent protection device used for first and second output insulated gate semiconductor devices driven by a signal, comprising: a source electrode of the first output insulated gate semiconductor device via a positive temperature coefficient thermistor; The source electrodes of the second output insulated gate semiconductor device are connected to each other, and the gate electrode of the first output insulated gate semiconductor device and the source of the second output insulated gate semiconductor device are connected to each other. A first drive element connected between the electrodes and configured to lower the gate voltage of the first output insulated gate semiconductor device by increasing the voltage across the positive temperature coefficient thermistor; The second output insulated gate type semiconductor device is connected between the gate electrode of the power insulated gate type semiconductor device and the source electrode of the first output insulated gate type semiconductor device, and the voltage across the positive temperature coefficient thermistor rises. A second driving element for lowering the gate voltage of the semiconductor device; and a voltage dividing series circuit composed of a plurality of high resistances connected in parallel with the positive temperature coefficient thermistor, and a low voltage side terminal of the light receiving element array. Is connected to a predetermined voltage dividing point of the voltage dividing series circuit. 4. The overcurrent protection device according to claim 1, wherein said PTC thermistor is thermally coupled to said insulated gate semiconductor device. 5. The semiconductor device according to claim 1, wherein the driving element is thermally coupled to the insulated gate semiconductor device.
The overcurrent protection device as described.