JP2002110866A - Electronic equipment - Google Patents

Abstract

(57) Abstract: Provided is an electronic device in which a temperature rise due to a protection function operation of a power semiconductor element is reduced and reliability is improved. SOLUTION: A load 1, a power semiconductor element 2 for driving the load, a temperature detection circuit 3 for detecting a temperature of the power semiconductor element, and a shutoff circuit for shutting off the power semiconductor element based on a detection result by the temperature detection circuit. And a load state detection circuit 5 for detecting a load state. When the load state detection circuit detects that the load is in a short-circuit state, the diode 201 of the plurality of diodes 201 to 206 in the temperature detection circuit is provided. Is turned on, the set value of the detected temperature is changed to a lower value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic device having a built-in temperature protection function for driving and controlling a load.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a configuration example of a conventional electronic device having a built-in temperature protection function.

In FIG. 3, 1 is a load, 2 is a power semiconductor element, 3 is a temperature detection circuit, 4 is a cutoff circuit, and 5 is a load state detection circuit. As shown in FIG. 2, a load 1 has one terminal connected to a power supply line 6 and the other terminal connected to a power semiconductor element 2 (here, an N-channel power MOSF).
ET is used and is connected to a power MOSFET hereinafter.

The power MOSFET 2 has a source terminal G
It is connected to the ND line 8 and is controlled by a gate control circuit 9 connected to the gate to ON / OFF operation.

The gate control circuit 9 receives a signal from the load state detecting circuit 5 and, when the load 1 is in a normal state, receives an input signal from the external device 200 (for example, a microcomputer) to the electronic device 7. Power MOSFE
The gate voltage is oscillated when the load is in a short-circuit state so as to be applied to the gate of T2.

The load state detection circuit 5 determines the state of the load by detecting the voltage across the load 1 and outputs a signal to the gate control circuit 9 if the load is short-circuited.

The temperature detecting circuit 3 utilizes the temperature change characteristic of the forward voltage VF of the diode. The diode 101 and the resistor 102 are connected to a constant voltage source, and when the temperature rises, the forward voltage VF of the diode 101 becomes higher. When the temperature of the electronic device 7 reaches the set overheat detection temperature, a signal is output from the output terminal 103 to the input terminal 104 of the shut-off circuit 4 when the temperature of the electronic device 7 reaches the set overheat detection temperature.

The shutoff circuit 4 includes a resistor 105 and a MOSFET.
When a voltage signal equal to or higher than the threshold voltage of the MOSFET 106 is input from the temperature detection circuit 3 to the input terminal 104, the MOSFET 106 is turned on, and the gate voltage of the power MOSFET 2 is reduced and the OF MOSFET 2 is turned off.
It becomes F.

[0009] In such a configuration, an abnormal state such as an abnormal rise in the use environment temperature or abnormal heat generation of other devices occurs.
When the temperature of the electronic device 7 rises above the set value, the temperature rise is detected by the temperature detection circuit 3, and the power MOSFET 2 in the output stage is turned off by the cutoff circuit 4.

[0010]

However, in the conventional configuration, if the load short-circuit state continues for a long time, there is a problem that the temperature of the electronic device rises and the reliability of the device decreases. That is, there has been a problem that the protection function operation of a power semiconductor element such as a power MOSFET causes self-heating to increase the temperature and reduce the reliability.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an electronic device in which a temperature rise due to a protection function operation of a power semiconductor element is reduced and reliability is improved. It is in.

[0012]

In order to achieve the above object, an electronic device according to the present invention comprises a load, a power semiconductor element for driving the load, a temperature detection circuit for detecting the temperature of the power semiconductor element, The power supply device further includes a cutoff circuit that cuts off the power semiconductor element based on a detection result by the temperature detection circuit, and a load state detection circuit that detects a state of the load, wherein the temperature detection circuit detects a load detected by the load state detection circuit. It is characterized in that the set value of the detected temperature is changed according to the state.

In this electronic device, the temperature detection circuit includes:
When the load state detected by the load state detection circuit is a short circuit state, the set value of the detected temperature is reduced.

In this case, the temperature detecting circuits are connected in series in the forward direction to each other, are supplied with a constant voltage, and have a plurality of diodes each having a predetermined forward voltage temperature coefficient, and are connected in series with the plurality of diodes to detect the constant voltage. A resistance element for dividing the voltage and supplying the divided voltage to the interruption circuit; and a switch element connected in parallel with at least one of the plurality of diodes. Is preferably conducted.

Further, the load state detecting circuit may be configured to detect a voltage across the load or to detect a drain voltage of a power MOSFET which is a power semiconductor element. Load state detection circuit is a power MOSFET
Is configured to detect the drain voltage of
An SFET, a load state detection circuit, a temperature detection circuit, a cutoff circuit, and a control circuit for a power MOSFET can be formed on the same semiconductor substrate, and only three terminals, namely, a load connection terminal (output terminal), a GND terminal, and an input terminal Thus, a semiconductor device that drives and controls a load can be realized. Thus, the number of components can be reduced, and the reliability of the device can be improved.

According to the above configuration, the detection temperature at which the power semiconductor element is turned off can be changed according to the state of the load, and when the load is short-circuited and the protection function is activated, the load state is detected. Based on a signal from the circuit, the temperature detection circuit operates the cutoff circuit to lower the overheat detection temperature at which the power semiconductor element is turned off. As a result, it is possible to realize an electronic device in which the temperature rise due to the protection function operation of the power semiconductor element is reduced and the reliability is improved.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a block diagram showing a configuration of an electronic device according to a first embodiment of the present invention.

In FIG. 1, 1 is a load, 2 is a power semiconductor element, 3 is a temperature detection circuit, 4 is a cutoff circuit, and 5 is a load state detection circuit.

The load 1 has one terminal connected to the power supply line 6 and
The other terminal is connected to the power semiconductor element 2. In this embodiment, an N-channel power MOSFET is used as the power semiconductor element 2 as in the conventional example, and is simply referred to as a power MOSFET hereinafter. However,
As the power semiconductor element 2, in addition to the power MOSFET, an IGBT (insulated gate bipolar transistor)
Alternatively, a normal bipolar transistor may be used. The power MOSFET 2 has a source terminal connected to the GND line 8.
The gate terminal is connected to the output terminal of the gate control circuit 9.

The gate control circuit 9 receives a signal from the load state detection circuit 5 and, when the load 1 is in a normal state, inputs a signal from the external device 200 (for example, a microcomputer) to the electronic device 7. When the load 1 is in a short-circuit state, the gate voltage oscillates so that the gate voltage is directly applied to the gate terminal of the power MOSFET 2 via the resistor 105. In this embodiment, the gate voltage is oscillated. However, the gate voltage may be limited to a predetermined value and the load current may be limited to a predetermined value. Generally, while the load 1 is in the short-circuit state, there are a method of completely interrupting and latching the load current, a method of oscillating the load current, and a method of limiting the load current to a predetermined value. Regarding the method of completely interrupting the load current, heat cannot be generated when the load is short-circuited. The present invention is effective when a method of oscillating the load current or a method of limiting the load current to a predetermined value is used.

The load state detection circuit 5 determines the state of the load by detecting the voltage across the load 1. When the load 1 is normal, a potential difference equal to the power supply voltage is generated at both ends of the load 1 (in this case, the power MOSF).
Since the on-resistance of ET2 is sufficiently smaller than the resistance value of load 1, since almost no voltage is generated at both ends of load 1 when load 1 is in a short-circuit state, a load state detection circuit utilizing this difference is used. 5 outputs a signal indicating a short-circuit state to the gate control circuit 9 and the temperature detection circuit 4 when the load 1 is in a short-circuit state.

The temperature detecting circuit 3 utilizes a temperature change characteristic (for example, 2 mV / ° C.) of the forward voltage VF of the diode. Six diodes 201 to 206 (for example, VF = 0.6 V (at a current of 10 μA)) and a resistor 207 (for example, when the resistance value is 100
kΩ) in series, and a diode 206 and a resistor 207 are connected.
Are connected to the output terminal 208.

The temperature detecting circuit 3 of the present embodiment is different from the conventional example in that the drain and the source of the MOSFET 209 are connected to the anode and the cathode of the diode 201, respectively, based on the output signal of the load state detecting circuit 5. In that the diode 201 is short-circuited. As a result, the heating detection temperature changes from 150 ° C to 115 ° C.
About 35 ° C. That is, the configuration is such that the number of diodes, that is, the detected temperature can be changed according to the state of the load. This will be specifically described below.

In this embodiment, the number of diodes to be short-circuited is one, but may be two or more. For example, if two diodes are short-circuited,
The detected temperature drops by about 88 ° C. to 62 ° C. Further, the number of MOSFETs that short-circuit the diode may be increased so that three or more detected temperatures can be set according to the size of the load.

The shutoff circuit 4 includes a resistor 105 (for example, a resistance value of 10 kΩ) and a MOSFET 106.
When a voltage signal equal to or higher than the threshold voltage of T106 (for example, 0.9 V) is input, the MOSFET 106 is turned on and the input terminal of the gate control circuit 9 is connected to GND.
Therefore, the power MOSFET 2 is turned off because the gate voltage decreases.

Next, the operation of the electronic device 7 configured as described above will be described.

When the load 1 is in a normal state, a signal of logic "L" level is output from the load state detection circuit 5, and the MOSFET 209 of the temperature detection circuit 3 is in an OFF state. When the temperature rises in this state, each diode 2
The forward voltage VF of 01 to 206 decreases at a temperature characteristic of 2 mV / ° C. When the temperature of the electronic device 7 reaches 25 ° C., which is a normal temperature, to 150 ° C. set as the overheat detection temperature Td, the forward voltage of all six diodes becomes 1.5 (= 6).
× 0.002 × (150-25)) V, and the voltage applied between the diodes 201 to 206 becomes 2.1 (= 6 ×
0.6-1.5) V.

As a result, since the voltage Vz of the constant voltage source of the temperature detection circuit 3 is 3 V, a voltage of 0.9 V is generated across the resistor 207. That is, the temperature detection circuit 3
From the output terminal 208 of the MOSFET 1
At 06, a voltage signal of 0.9 V which is the threshold voltage is output. As a result, the MOSFET 106 is turned on, and the power MOSFET 2 is turned off because the gate voltage decreases. When the load is normal, the power MOSFET 2 is turned off at 150 ° C. in this way.

On the other hand, when the load is short-circuited, a signal of logic "H" level is output from the load state detecting circuit 5,
The MOSFET 209 of the temperature detection circuit 3 is turned on. Therefore, the diode 201 is short-circuited, and if the temperature rises in this state, the five diodes 202 to 20
6, the forward voltage VF decreases at a temperature characteristic of 2 mV / ° C. 0.9V voltage is output from the temperature detection circuit 3,
The power MOSFET 2 is turned off by the cutoff circuit 4 via the gate control circuit 9 when a potential difference of 0.9 V is generated between both ends of the resistor 207, and the voltage applied to the five diodes 202 to 206 is 2.1V. Is reached. That is, from the relational expression of 5 × (0.6−0.002 × (Td−25)) = 2.1, when the diode 201 is short-circuited,
The heating detection temperature Td is 115 ° C. Therefore, when the load 1 is short-circuited, the heating detection temperature Td changes from 150 ° C. to 115 ° C.
And 35 ° C.

As described above, when the load is short-circuited,
By changing the number of temperature detecting diodes in the temperature detecting circuit 3 and changing the detected temperature level, even if the load short-circuit state is continued, if the temperature exceeds 115 ° C. which is 35 ° C. lower than the set overheating temperature of 150 ° C. Therefore, the reliability of the device can be greatly improved.

(Second Embodiment) FIG. 2 is a block diagram showing the configuration of an electronic device according to a second embodiment of the present invention.
Here, the present embodiment is different from the first embodiment in that the load state detection circuit 5 does not detect the voltage across the load 1 but detects the drain voltage when the power MOSFET 2 is on. By doing so, the state of the load is detected. The other configuration is the same as that of the first embodiment, and thus the same reference numerals are given and the description is omitted.

In FIG. 2, a load state detecting circuit 5 includes resistors 301 and 302 for detecting the drain voltage of the power MOSFET 2, and a MOSFET 30 in which a detection voltage divided by the resistors 301 and 302 is supplied to the gate.
4. Load resistance 303 of MOSFET 304, MOSFET
MOSFET 306, the gate of which is supplied with the potential of the connection point between T304 and load resistor 303, load resistor 305 of MOSFET 306, and MOSFET 306 and load resistor 30
5 is connected to the gate of the MOSFET 304 and the load potential of the load resistor 303 to the drain.
It is composed of an FET 307.

Next, the operation of the load state detecting circuit 5 configured as described above will be described.

When the power MOSFET 2 is on, a high-level voltage signal is always input to the input terminal of the electronic device 7. This voltage is applied to the load resistor 30
3 and 305 to a common connection, and a load state detection circuit 5
The load state detection circuit 5
Has a configuration in which the circuit operates only when the power MOSFET 2 is in the ON state.

Further, when the load 1 is normal, the drain voltage of the power MOSFET 2 becomes a value close to the GND voltage, but when the load 1 is short-circuited, the drain voltage rises to near the power supply voltage. By utilizing this difference in voltage, the load state detection circuit 5 outputs a signal indicating the short circuit state to the gate control circuit 9 and the temperature detection circuit 3 when the load 1 is in the short circuit state.

As described above, when the load state is detected, by detecting the drain voltage of the power MOSFET 2, the power MOSFET 2, the load state detection circuit 5, the temperature detection circuit 3, the cutoff circuit 4, the gate control circuit 9 Can be formed on the same semiconductor substrate, and the semiconductor device 400 has only three terminals, ie, a load connection terminal (output terminal) 401, a GND terminal 402, and an input terminal 403.
Can be realized. As a result, the number of parts can be reduced, and a great effect of improving the reliability of the device can be obtained.

In the present embodiment, the load state detecting circuit 5 uses a resistance dividing circuit composed of the resistors 301 and 302. However, this is merely an example, and a diode may be used for one of them. A combination of a diode and a resistance dividing circuit may be used.

Further, the load state detecting circuit 5 has a power MO
Although the load state is detected by using the SFET 2 in the ON state and using the input voltage of the electronic device 7 as the power supply voltage, a circuit for detecting the ON state may be separately provided. That is, any other circuit configuration may be used as long as the circuit can detect the drain voltage of the power MOSFET 2 when the power MOSFET 2 is on.

[0040]

As described above, according to the present invention,
By changing the overheat detection temperature in accordance with the state of the load, the temperature rise due to the operation of the protection function of the power semiconductor element is improved, and a special effect is obtained in that the reliability of the electronic device can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an electronic device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an electronic device according to a second embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration example of a conventional electronic device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Load 2 Power semiconductor element 3 Temperature detection circuit 4 Interruption circuit 5 Load state detection circuit 6 Power supply line 7 Electronic device 8 GND line 9 Gate control circuit 105 Resistance 106 MOSFET 200 External device 201 to 206 Diode 207 Resistance 208 Temperature detection circuit 3 Output terminal 209 MOSFET for short-circuiting diode 210 Input terminal of blocking circuit 4 400 Semiconductor device

Claims (5)

[Claims] A load, a power semiconductor element for driving the load, a temperature detection circuit for detecting a temperature of the power semiconductor element, and a power semiconductor element in a cut-off state based on a detection result by the temperature detection circuit. An interrupting circuit, and a load state detecting circuit that detects a state of a load, wherein the temperature detecting circuit changes a set value of the detected temperature according to a state of the load detected by the load state detecting circuit. Electronic device characterized by. 2. The electronic device according to claim 1, wherein the temperature detection circuit reduces the set value of the detected temperature when the load state detected by the load state detection circuit is in a short-circuit state. apparatus. 3. The temperature detection circuit includes a plurality of diodes connected in series in a forward direction to each other and supplied with a constant voltage, each having a predetermined forward voltage temperature coefficient, and the plurality of diodes connected in series with the plurality of diodes. A resistance element for dividing a voltage and supplying the divided voltage to the cutoff circuit, and a switch element connected in parallel with at least one of the plurality of diodes,
The electronic device according to claim 1, wherein the load state detection circuit turns on the switch element when detecting that the load is in a short circuit state. 4. The electronic device according to claim 1, wherein the load state detection circuit detects a voltage between both ends of the load. 5. The power semiconductor device according to claim 1, wherein the power semiconductor device is a power MOSFET.
T, wherein the load state detection circuit includes the power MO
The electronic device according to claim 1, wherein a drain voltage of the SFET is detected.