JP2001095148A - Method for protection of semiconductor relay system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly count the number of times of self-interruption due to heat generation of a MOSFET with a heat interruption circuit built in. SOLUTION: This semiconductor relay system supplies electric power to a load by an ON/OFF control which is conducted by applying charge pump output voltage obtained by stepping up power supply voltage with a charge pump circuit, by means of a microcomputer to the gate of a MOSFET with a heat interruption circuit built in through a driving circuit. The current supplied to the load is detected and, if it is larger than a reference set value higher than a rated current value, a driving circuit is controlled to cut off the voltage applied to the gate of the MOSFET for stopping power supply to the load. When the source voltage occurring on the source side of the MOSFET is detected and a command signal to turn on the MOSFET is outputted from the microcomputer, the number of times when the source voltage occurring on the source side of the MOSFET is lower than the reference voltage value is counted and, if the count reaches the preset number of times, the semiconductor relay system is turned off to prevent generation of resetting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a MOSFET with a built-in thermal cut-off circuit which turns off a MOSFET with a built-in thermal cut-off circuit when an overcurrent flows through a lamp load so as to prevent current from flowing through the lamp load. In particular, a MOS relay with a built-in thermal cutoff circuit is provided by a cutoff function of a self-heat cutoff circuit built in a MOSFET with a built-in thermal cutoff circuit in a state where a current limit is applied to a predetermined current value.
M with built-in thermal cutoff circuit when FET is repeatedly turned off
The present invention relates to a method for protecting a semiconductor relay system, which can prevent an OSFET from being destroyed and prevent a failure from occurring in the semiconductor relay system.

[0002]

2. Description of the Related Art Generally, in a vehicle, power from a vehicle-mounted battery is supplied to loads disposed in various parts of the vehicle via a power line covered with a power MOSFET and an insulating film. This power line is routed along the vehicle body in an engine room or the like that is constantly vibrating. At this time, if the power line is located close to a corner of the vehicle body, for example, the power line is intermittently connected to the corner due to vibration. The contact of the power supply line is repeated for a long time, and the coating of the power supply line is gradually cut off by the corners of the vehicle body, so that the inner conductor is exposed though it is minute. As a result, a dead short or a rare short occurs in the power supply line due to contact with the vehicle body, and an overcurrent flows.

In recent years, as a semiconductor relay for automobiles,
Power MOSFET and IPS (Intelligent Power Swit
ch) has been used. Such a semiconductor relay,
In the IPS, various current limiter methods are conventionally employed as shown in FIG. 2 to prevent heat generation of the device. For example, if an overcurrent flows for some reason (for example, ground fault) while energizing the lamp load (during supply of a steady current), the current flowing to the lamp load is reduced to zero. For this reason, sampling the current value at a predetermined interval using a microcomputer and reading the current monitor value, and judging in a software manner whether or not an overcurrent state occurs, means that the sampling is performed when the current flowing to the lamp load is zero. could not.

Such a semiconductor relay system has a built-in self-heat shutoff circuit as a switching element, and when the temperature exceeds a predetermined temperature, the self-cutoff function turns off regardless of the voltage applied to the gate.
When the ET is used, if a current larger than a predetermined current flows for some reason (for example, ground fault) while energizing the lamp load (during supply of a steady current), the load is usually applied to the lamp load for a predetermined time. The MOSFET with built-in thermal shutdown circuit is shut off by detecting that the current has flowed, but the MOSFET with built-in thermal shutdown circuit can be shut down without detecting the overcurrent flowing to the lamp load.
Current continues to flow through the MOSFET and the MOSFET with a built-in heat shut-off circuit heats up. When the temperature exceeds its own heat cut-off temperature, the MOSFET with a built-in heat cut-off circuit self-cuts off and stops supplying current to the lamp load. The situation in which no current is supplied to the lamp load as described above includes the interruption of the MOSFET with a built-in thermal cutoff circuit based on normal overcurrent control and the M
There is an interruption of a MOSFET with a built-in heat interruption circuit based on self-interruption due to heat generation of the OSFET. In both cases, the current supply to the lamp load is stopped by turning off the MOSFET with a built-in thermal cutoff circuit.

On the other hand, MOSFETs with a built-in thermal cut-off circuit have a life span, and are particularly vulnerable to thermal stress. Leads to destruction. In other words, this MOSFET with a built-in thermal cutoff circuit
There is a life due to the number of self-interruptions that are repeated each time the temperature exceeds the heat-interruption temperature due to thermal stress. In particular, when repeated in a low-temperature (below freezing) atmosphere many times, it takes time for the temperature of the MOSFET with a built-in heat-blocking circuit to rise from the low-temperature (below freezing) atmosphere to the heat-blocking temperature, and heat is blocked from normal temperature. The temperature of the MOSFET with a built-in thermal cutoff circuit is subjected to more thermal stress than the temperature rises up to the temperature. Therefore, the MOSFE with a built-in heat cutoff circuit in a low temperature (below the freezing point) atmosphere
The repetition of the self-interruption of T is more strict in the number of times than the self-interruption of the MOSFET with a built-in thermal shutdown circuit at room temperature.

When self-interruption is repeated many times in a low-temperature (below freezing) atmosphere, especially when heat generated in the chip is transmitted to the stem, the MOSFET with a built-in thermal shutdown circuit is damaged by thermal stress (for example, Endurance times). As a cause of this destruction, the temperature of the device rises instantaneously, and repeatedly exceeds Tch (four-channel temperature), the Al junction fatigues and the resistance increases, so that heat generation is further accelerated and the Al electrode layer melts. Due to the difference in thermal expansion between the Al spike that diffuses into silicon and causes a failure and the material of the package and the material forming the chip, the Al at the chip corner
There is an Al slide that leads to failure due to sliding of the wiring.

[0007]

If the MOSFET with a built-in thermal cutoff circuit is destroyed, the reliability of the entire semiconductor relay system used as a switching element becomes a problem. Therefore, it is necessary to count the number of times that the MOSFET with a built-in thermal cutoff circuit has self-blocked due to thermal stress, and to perform processing such as issuing a warning before the MOSFET with a built-in thermal cutoff circuit is destroyed. . However, the interruption of the MOSFET with a built-in thermal cut-off circuit is performed based on ordinary overcurrent control,
In some cases, it is based on self-interruption due to heat generation of T. Conventionally, the two cannot be distinguished from each other.
There has been a problem that the number of times the OSFET has undergone self-interruption due to thermal stress cannot be counted.

An object of the present invention is to provide a MOS having a built-in thermal cutoff circuit.
An object of the present invention is to accurately count the number of self-interruptions caused by heat generated by an FET.

[0009]

According to a first aspect of the present invention, there is provided a method for protecting a semiconductor relay system, comprising the steps of: In a semiconductor relay system that supplies power to a load by applying on / off control by applying a boosted charge pump output voltage to the gate of the MOSFET with a built-in thermal shutdown circuit via a drive circuit, the voltage is supplied to the load. When the current is detected and the current is larger than a reference set value set in advance to a current value higher than the rated current value, the drive circuit is controlled to cut a voltage applied to the gate of the MOSFET with a built-in thermal shutdown circuit. Off to stop supplying power to the load, and
When a command signal for detecting the source voltage generated on the source side of the FET and turning on the MOSFET with a built-in thermal cutoff circuit is output from the microcomputer, it is generated on the source side of the MOSFET with a built-in thermal cutoff circuit. The semiconductor relay system counts that the source voltage is lower than a preset reference voltage value, and when the preset number of times is reached, the semiconductor relay system is turned off to prevent resetting. With this configuration, according to the first aspect of the present invention, it is possible to accurately count the number of times of self-interruption due to heat generation of the MOSFET with a built-in thermal shutdown circuit.

In order to achieve the above object, in a semiconductor relay system protection method according to a second aspect of the present invention, a built-in self-heat shut-off circuit is operated in which a set number of times is determined by characteristics of a MOSFET with a built-in heat shut-off circuit. The number is set to a number smaller than the number of times of destruction due to repeated interruption. With this configuration, according to the second aspect of the present invention, it is possible to accurately count the number of times of self-interruption due to heat generation of the MOSFET with a built-in thermal shutdown circuit.

[0011]

Embodiments of the present invention will be described below. FIG. 1 shows an embodiment of a protection method for a semiconductor relay system according to the present invention.

In FIG. 1, a power supply voltage VB from a vehicle-mounted battery 1 includes a current detecting resistor (shunt resistor) Rs for detecting a current supplied to a load, and a drain D of a MOSFET 2 with a built-in heat cutoff circuit as a semiconductor switch element. To the lamp load 3 such as a stop lamp via the source S; This MOSFET 2 with a built-in thermal cutoff circuit
For example, a logic level (4 V or more) drive type power MO
The SFET has a built-in thermal cutoff circuit, which enables protection of the power MOSFET in the overheated state. The overheat cutoff method is a latch type, and the gate voltage is 0 after the overheat cutoff circuit is activated.
It returns with a bias.

The drive circuit 4 has a charge pump output voltage VP obtained by boosting the power supply voltage VB by the charge pump circuit 5.
NPN type switching (SW) in which is connected to the collector
It has a transistor Tr1 and an NPN-type switching (SW) transistor Tr2 in which the collector is connected to the emitter of the SW transistor Tr1, and the contact between the emitter of the SW transistor Tr1 and the collector of the SW transistor Tr2 has a built-in thermal cutoff circuit. Connected to the gate G of the MOSFET 2. Then, the driving circuit 4
By turning on the W transistor Tr1 and turning off the SW transistor Tr2, the charge pump output voltage VP supplied from the charge pump circuit 5 is applied to the gate G of the MOSFET 2 with a built-in thermal cutoff circuit. Turn on. Also, S
By turning off the W transistor Tr1 and turning on the SW transistor Tr2, the application of the charge pump output voltage VP to the gate G of the MOSFET 2 with a built-in thermal shutdown circuit is stopped, and the MOSF with a built-in thermal shutdown circuit is turned off.
Turn off ET2.

Also, a shunt resistor Rs provided between the vehicle-mounted battery 1 and the MOSFET 2 with a built-in thermal cutoff circuit is provided.
Is a low resistance for converting the current IL flowing through the power supply line between the vehicle-mounted battery 1 and the load 3 into a voltage, and detects the current IL flowing through the power supply line by detecting the voltage between both ends. Both ends of the shunt resistor Rs are connected to a (+) input terminal and a (-) input terminal of the differential amplifier 6, and the differential amplifier 6 functions as a current detecting means, and detects a voltage between both ends of the shunt resistor Rs. The current IL is detected by outputting a corresponding voltage. The shunt resistor Rs uses a resistor of, for example, several tens of mΩ, and determines a hard overcurrent determination value (first set value), for example, several tens of amperes.

The output of the differential amplifier 6 is digitally converted by an A / D converter 7 built in a microcomputer (microcomputer) 8 and taken into the microcomputer (microcomputer) 8. One end of the microcomputer 8 is connected to the ground via a resistor R1, and the other end is connected to a power supply voltage VB.
Is connected, and when the switch SW is turned on, an H-level ON operation signal S1 is supplied. The microcomputer 8 has a built-in A / D converter 7 and operates according to a preset control program. The ROM 9 stores a control program for the CPU 9 in advance.
RA for temporarily storing data required during execution of operation 9
M11, and the microcomputer 8 sends an H-level ON operation signal S1 to the microcomputer 8 by turning on the switch SW.
Has a function of outputting a drive instruction signal S2 to the gate / logic circuit 13 when is input.

On the other hand, both ends of the shunt resistor Rs are connected to input terminals of a comparator 12, respectively, and an output terminal of the comparator 12 is connected to a gate logic circuit 13. The gate logic circuit 13 is connected to the drive circuit 4 and the microcomputer (microcomputer) 8. Comparator 12
Outputs a predetermined voltage to the gate logic circuit 13 according to the voltage across the shunt resistor Rs (output when the current value flowing through the shunt resistor Rs reaches a preset current value). When there is an output from the comparator 12, the gate logic circuit 13 turns off the gate voltage applied from the drive circuit 4 to the gate G of the MOSFET 2 with a built-in heat cutoff circuit regardless of the drive instruction signal S2 from the microcomputer 8. Perform output. As a result, the shunt resistance Rs
The current flowing through is reduced. After receiving the output from the comparator 12, the hysteresis of the comparator 12 causes the current flowing through the shunt resistor Rs to reach a predetermined amount (hysteresis amount) from the initially flowing current. Built-in MOS
An ON signal is output so as to apply a gate voltage to the gate G of the FET2. This current control continues until the drive instruction signal S2 output from the microcomputer 8 to the gate logic circuit 13 is turned off.

Further, one end of a resistor 14 is connected to the source S of the MOSFET 2 with a built-in thermal cutoff circuit, and the other end of the resistor 14 is grounded. This resistor 14 is a detection resistor for detecting the voltage Vk generated at the source S of the MOSFET 2 with a built-in thermal cutoff circuit. This resistor 14
Is connected to the microcomputer 8 via a noise cut filter constituted by a resistor 15 and a capacitor 16. When the MOSFET 2 with a built-in heat cutoff circuit is turned on, the source voltage Vk of the resistor 14
4 and the voltage value determined by the applied voltage is reduced to almost zero potential when the MOSFET 2 with a built-in thermal cutoff circuit is turned off.

The microcomputer 8 constantly samples the output of the differential amplifier 6 digitally converted by the A / D converter 7 every predetermined time (for example, several msec), and outputs a current IL flowing through the sampled load. Is microcomputer 8
It is compared whether the current IL flowing through the lamp load 3 exceeds the reference set value (for example, several times). Sometimes overcurrent is detected. Upon detecting this overcurrent, the microcomputer 8 sets the gate logic circuit 1
Then, the output of the drive instruction signal S2 to S3 is stopped. When the drive instruction signal S2 from the microcomputer 8 to the gate logic circuit 13 is turned off, the application of the charge pump output voltage VP to the gate G of the thermal FET 2 is stopped.

The operation of the overcurrent cut-off detecting device for a semiconductor relay system and the method for protecting the semiconductor relay system will be described. In the configuration shown in FIG. 1, the hardware overcurrent determination value is set to several tens of amps, and in the case of a ground fault, the current is limited at a period of about several tens μsec. Also, the soft overcurrent determination value is set to twice the rated load (21 W × two lamps) current, and the hysteresis of the comparator 12 is set. In this way, the soft overcurrent determination value is set to twice the rated load current, and the comparator 12
When the hysteresis is set, the drop of the current becomes the lower limit value. Therefore, the microcomputer 8 monitors the current (samples the current value) (compares with the overcurrent determination value set in the microcomputer 8) to set the overcurrent state. Can be read. In this case, the data sampling by the microcomputer 8 is regarded as an overcurrent state by reading several times for several msec, for example.

As described above, in the present embodiment, the constant current control is performed on the supply current to the load side against the overcurrent due to the short circuit on the load side, so that the current value is determined by the microcomputer as the overcurrent determination value (reference setting). Value), without over-current detection (comparison of the reference set value and the detected current value), and after detecting the over-current, the gate voltage of the MOSFET with built-in thermal shutdown circuit is dropped for a certain period of time, The MOSFET with a built-in cutoff circuit is turned off so that no current flows to the load side. This is the overheat control interruption by the overcurrent.

In addition, in response to an overcurrent due to a short circuit on the load side, the MOSFET itself with the built-in heat shut-off circuit is not turned on until the gate voltage of the MOSFET with the built-in heat shut-off circuit is turned off for a certain period of time to turn off the MOSFET with the built-in heat cut-off circuit. If the microcomputer 8 is overheated to a predetermined temperature, the self-heat shutoff function of the microcomputer 8 turns off the MOSFET with a built-in heat shutoff circuit before outputting the off signal from the microcomputer 8. Alternatively, since a rare short circuit occurs on the load side and overcurrent detection is not complete, overcurrent detection is not performed.
MOS with built-in thermal cutoff circuit by dropping the gate voltage of FET
The control to turn off the FET is not applied, and the heat shutoff circuit built-in type M
The OSFET itself is overheated and the temperature is raised to the overheat cut-off temperature, and in the absence of the output of the off signal from the microcomputer 8, the self-heat cut-off function of the self-built-in type MO cut-off type MO
Turn off the SFET. This is overheat self-interruption due to overcurrent.

The overheating control interruption by the overcurrent and the overheating self-interruption by the overcurrent are defined by a MOSFE built-in MOSFE.
It is the same in that T is turned off, but the former does not apply thermal stress to the MOSFET with a built-in thermal shutdown circuit, whereas the latter applies thermal stress to the MOSFET with a built-in thermal shutdown circuit. Have a big difference. The microcomputer 8 determines whether the overheating control is interrupted by the overcurrent or the overheating self-interruption is caused by the overcurrent. When the MOSFET with a built-in thermal cut-off circuit is turned off, the source side voltage Vk of the resistor 14 connected to the source S of the MOSFET 2 with a built-in thermal cut-off circuit drops to zero potential. This phenomenon is the same in the case of the overheat control interruption by the overcurrent and the case of the overheat self-interruption by the overcurrent. Therefore, when the microcomputer 8 outputs the drive instruction signal S2 for turning on the MOSFET with a built-in thermal cutoff circuit to the gate logic circuit, the microcomputer 8 reads the source side voltage Vk of the resistor 14 and reads the source voltage of the resistor 14 at this time. Whether the side voltage Vk is a constant voltage value,
See if it is almost zero potential. At this time, if the source side voltage Vk of the resistor 14 is substantially zero potential, it is determined that the MOSFET with a built-in thermal cutoff circuit has caused overheat self-cutoff due to overcurrent.

A MOSFET with a built-in thermal cut-off circuit normally operates for the life of an automobile unless it is subjected to thermal stress, but its life is shortened when it is subjected to thermal stress (self-interruption due to overheating). . In general, it is said that a MOSFET with a built-in heat shut-off circuit itself breaks down, for example, if it undergoes less than a predetermined number of times of self-heating in an atmosphere below freezing. That is, when self-interruption is repeated by receiving a thermal stress exceeding the heat-interruption temperature of its own, the MOSFET
T itself is destroyed.

If the MOSFET with a built-in thermal cutoff circuit is destroyed, the overall reliability of the semiconductor relay system used as a switching element becomes a problem. Therefore, the number of times that the MOSFET with a built-in heat shut-off circuit is subjected to thermal stress and self-cuts off is counted, and the MOSFET with a built-in heat cut-off circuit is counted.
It is necessary to perform processing such as issuing a warning before the SFET is destroyed. Therefore, in the microcomputer 8,
The overheating self-interruption due to the overcurrent is integrated and counted, and this count value is stored even when the power is turned off. The number of times that the safety is taken into consideration (for example, a predetermined number of times in an atmosphere below freezing) from the number of times until the MOSFET with a built-in thermal shutdown circuit is destroyed is set as the set number of times. Has reached the set number of times,
The microcomputer 8 turns off the semiconductor relay system itself to prevent resetting. By doing so, it is possible to replace the MOSFET before the MOSFET with the built-in thermal cutoff circuit receives thermal stress and breaks down. Furthermore, turn off the semiconductor relay system itself,
By preventing resetting, even if the MOSFET with built-in thermal shutdown circuit has reached a critical level,
It is possible to prevent a load short (ground fault) state from occurring many times and to prevent a failure from occurring in the wire harness.

[0025]

Since the present invention is configured as described above, it has the following effects.

According to the first aspect of the present invention, it is possible to accurately count the number of times of self-interruption due to heat generation of the MOSFET with a built-in thermal shutdown circuit.

According to the second aspect of the present invention, it is possible to accurately count the number of times of self-interruption due to heat generation of the MOSFET with a built-in thermal shutdown circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a method for protecting a semiconductor relay system according to the present invention.

FIG. 2 is a diagram showing characteristics of a conventional current limiter method.

[Explanation of symbols]

1 ……………………………………………………………………….
T3 ………………………………………………………………………………………………………………………………………………… Drive circuit 5 ……………………… Charge pump circuit 6 ……… …………………………………………………………………………………………………………… A / D converter 8 … CPU 10… ROM 11……… RAM 12 …… ……… Comparator 13 …………………………………………………………………………・ Logic circuit 14 ............ Resistance

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshikazu Nagashima 2464-48 Yazuzu, Kosai-shi, Shizuoka Yazaki Parts Co., Ltd. (72) Inventor Yoshihiko Mine 1 Toyota-cho, Toyota-shi, Aichi F-term Toyota Motor Co., Ltd. (Reference) 5G004 AA04 AB02 BA03 BA04 DA02 DA04 DC01 DC04 EA01 FA01 5G053 AA01 AA02 BA01 BA06 CA02 EA03 EB02 EC03 5J055 AX15 AX32 AX64 BX16 CX22 CX28 DX22 DX53 DX54 EX04 EX06 EX10 EX11 EX23 EZ17 EZ01 EZ01 EZ17 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ01 EZ43 EZ55 EZ57 FX04 FX07 FX13 FX18 FX21 FX31 FX32 FX38 GX01

Claims (2)

[Claims] 1. Using a MOSFET with a built-in thermal cutoff circuit,
A semiconductor relay that supplies power to a load by controlling on / off by applying a charge pump output voltage obtained by boosting a power supply voltage by a charge pump circuit by a microcomputer to a gate of the MOSFET with a built-in thermal cutoff circuit via a drive circuit. In the system, a current supplied to the load is detected, and when the current is larger than a reference set value set in advance to a current value higher than the rated current value, the drive circuit is controlled to control the drive circuit. The voltage applied to the gate of the MOSFET is cut off to stop the supply of power to the load, and a source voltage generated on the source side of the MOSFET with a built-in thermal cutoff circuit is detected to detect the source voltage of the MOSFET. When the command signal for turning on the MOSFET is output from the microcomputer, It counts that the source voltage generated on the source side of the built-in MOSFET is lower than a preset reference voltage value, and when the preset number of times is reached, the semiconductor relay system is turned off and reset is performed. A method for protecting a semiconductor relay system, wherein the protection is not performed. 2. The method according to claim 1, wherein the predetermined number of times is set such that the current is limited to a predetermined current value,
2. The protection method for a semiconductor relay system according to claim 1, wherein the number of times is less than the number of times of destruction caused by repetition of cut-off by operating a built-in self-heat cut-off circuit determined by the characteristics of the SFET.