JP5103335B2 - Switching element overheat protection device - Google Patents

Description

  The present invention relates to an overheat protection device for a switching element, and more particularly, a switching element in which a semiconductor chip is built in a case and the semiconductor chip temperature (chip temperature) at the start of switching and the case surface temperature are the same. Relates to an overheat protection device.

  In overheat protection of a switching element used in a power supply circuit (DC / DC converter or the like), thermal damage is generally prevented by a circuit using a temperature sensor (such as a thermistor) (see, for example, Patent Document 1). In Patent Document 1, an emitter is connected to a DC voltage input side, a collector is connected to a DC voltage output side, and a non-insulated switching having a switching transistor that operates on and off in response to a pulse voltage input from an oscillation circuit to a base. An overheat protection circuit provided in the regulator has been proposed. In this overheat protection circuit, a resistor is connected between the emitter and base of the switching transistor, a positive temperature coefficient thermistor is connected between the base and the output of the oscillation circuit, and switching is performed by increasing the resistance value when the switching transistor is in an overheated state. The transistor is turned off to provide overheat protection.

  Also, an overheat protection function semiconductor switch has been proposed which detects a temperature change of a power element (switching element) and reduces heat generation and thermal breakdown of the power element when an abnormal current flows in the main circuit (Patent Document 2). reference.). As shown in FIG. 4, this overheat protection function semiconductor switch shuts off the power element 51 provided in the main circuit through which the load current flows and the power element 51 when the amount of heat generated by the power element 51 exceeds an allowable range. And an overheat protection circuit 52. The overheat protection circuit 52 includes a shunt element 53, a temperature detection circuit 54, and a control circuit 55. The shunt element 53 is for flowing a current (a shunt current) at a predetermined ratio with respect to the magnitude of the current (load current) flowing through the power element 51, and is configured by, for example, an n-channel MOSFET. The shunt element 53 is connected in parallel to the power element 51 through an external circuit (not shown) that sets the shunt current to be smaller than the current flowing in the power element 51 at a predetermined ratio. The shunt element 53 is turned on or off according to a signal input to the gate terminal, and the overheat protection circuit 52 is opened and closed by this control.

The control circuit 55 adjusts the overheat protection level of the power element 51 based on the signal from the temperature detection circuit 54 and shuts off the main circuit while the power element 51 exceeds at least the overheat protection level. The power element 51 sets an overheat protection level signal suitable for the use environment temperature from a signal corresponding to the temperature of the shunt element 53 before the shunt current flows.
JP 2002-142449 A JP 2003-188267 A

  When performing overheat protection of a switching element, originally, it is desired to protect the switching element by directly measuring the chip temperature, but the chip temperature cannot be directly measured with a commonly used element. Therefore, the case temperature and the ambient temperature of the switching element are measured, and a temperature difference is generated between the chip temperature and the measured temperature. Therefore, the temperature difference is estimated and the measured temperature is used for protection. The worst case temperature difference (maximum difference) should be used.

  For example, when the difference between the chip temperature and the case temperature is 60 K at the maximum, the protection temperature is the chip temperature upper limit value −60 K or less. If the chip temperature upper limit is 150 ° C., the protection temperature is 90 ° C. Therefore, with this setting, in a situation where the ambient temperature exceeds 90 ° C., the system cannot even start switching of the switching element.

  In Patent Document 2, since the overheat protection level signal suitable for the use environment temperature is set from the signal corresponding to the temperature of the shunt element 53 before the shunt current flows, the overheat protection accuracy is compared with the case where the use environment temperature is not considered. Will improve. However, since the power element 51 constituting the overheat protection function semiconductor switch is always switched when power is supplied to the load Z, the previous switching is continued even if the ambient temperature is the same when the switching is started. The temperature of the power element 51 varies depending on the time and the elapsed time from when switching is stopped. Therefore, if the temperature of the power element 51 is estimated from the ambient temperature or the case surface temperature of the semiconductor switch, the estimation accuracy is deteriorated. Therefore, it is an essential requirement to provide the shunt element 53, and the configuration is complicated accordingly.

  The present invention has been made in view of the above-described conventional problems, and the purpose thereof is to enable overheat protection of a switching element in which switching is started in a state where the chip temperature and the case temperature are the same as compared with the conventional one, In addition, it is an object of the present invention to provide an overheat protection device for a switching element that can start operation even when the ambient temperature is higher than that of the prior art.

  In order to achieve the above object, according to the first aspect of the present invention, the semiconductor chip for switching is built in the case, and the temperature of the semiconductor chip at the start of switching and the surface temperature of the case are the same. It is the overheat protection device of the switching element used. Then, temperature detection means capable of detecting the surface temperature of the case and threshold setting means for setting a threshold based on the detected temperature at the start of switching of the semiconductor chip detected by the temperature detection means are provided. In addition, after starting the switching of the semiconductor chip, a determination unit that determines whether or not the temperature of the semiconductor chip is equal to or higher than a temperature corresponding to the threshold set by the threshold setting unit, and the determination unit includes the temperature of the semiconductor chip Includes a stopping means for stopping the operation of the semiconductor chip when it is determined that the temperature is equal to or higher than the temperature corresponding to the threshold value. Here, “the semiconductor chip is built in the case” is not limited to a structure in which the semiconductor chip is simply housed in the case, but also includes a structure in which the semiconductor chip is resin-molded. Further, “the case can detect the surface temperature of the case” includes not only directly detecting the surface temperature of the case but also indirectly detecting the surface temperature of the case. The “temperature corresponding to the threshold value” is not necessarily set by the temperature of the semiconductor chip after the start of switching, but is the time until the semiconductor chip reaches a predetermined temperature (upper limit temperature) after the start of switching. Since it may be set, when the threshold is set by time, it means the temperature when the time has elapsed.

  In a switching element in which a semiconductor chip is built in a case, the case surface temperature when the temperature of the semiconductor chip reaches the upper limit standard temperature during switching of the semiconductor chip differs depending on the temperature at the start of switching. In this invention, the case surface temperature at the start of switching of the semiconductor chip is detected directly or indirectly by the temperature detecting means. For example, the case surface temperature is indirectly detected by detecting the temperature around the switching element. A threshold value is set by the threshold value setting unit based on the detection signal of the temperature detection unit, and after the start of switching, the determination unit determines whether the temperature of the semiconductor chip is equal to or higher than the temperature corresponding to the threshold value. When it is determined that the temperature of the semiconductor chip is equal to or higher than the temperature corresponding to the threshold value, the operation of the semiconductor chip is stopped. Therefore, overheating protection of the switching element in which switching is started in a state where the chip temperature and the case temperature are the same can be performed with higher accuracy than before, and the operation can be started even when the ambient temperature is higher than before.

  According to a second aspect of the present invention, in the first aspect of the present invention, the switching element is used in a backup circuit. In the present invention, when the switching element used in the backup circuit cannot supply power from the main circuit to the load, switching of the semiconductor chip is started and power is supplied to the load. The ambient temperature of the backup circuit rises when the switching element is switched in the main circuit, and the temperature of the switching element of the backup circuit rises in the same state as the chip temperature and the case surface temperature as the ambient temperature rises. Therefore, when the main circuit is stopped, until the semiconductor chip switching is started, the temperature of the switching element of the backup circuit becomes the same as the chip temperature and the case surface temperature, and the overheating protection of the switching element of the backup circuit The operation can be started even when the ambient temperature at the start of switching is higher than 90 ° C.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the threshold value setting means includes a case surface temperature when switching of the semiconductor chip is started, and a switching start obtained in advance. The threshold value is set based on the difference between the chip temperature and the case surface temperature thereafter. In the present invention, since the threshold is set based on the difference between the chip surface temperature and the case surface temperature that can be accurately estimated from the temperature at the start of switching, the overheat protection is more appropriately performed.

  According to the present invention, overheating protection of a switching element in which switching is started in a state where the chip temperature and the case temperature are the same can be performed more accurately than in the past, and the operation can be started even when the ambient temperature is higher than in the past. It is possible to provide an overheat protection device for a switching element.

  Hereinafter, an embodiment in which the present invention is embodied in a DC / DC converter as a power supply device that supplies power to a plurality of auxiliary machines (not shown) of a hybrid vehicle will be described with reference to FIGS.

  As shown in FIG. 1, the DC / DC converter 11 uses a high voltage main battery 12 as a power source, a main circuit 14 in which a primary side and a secondary side are insulated by a transformer 13, and an auxiliary battery 15 as a power source. And a backup circuit 16 to which the power of the auxiliary battery 15 is supplied via the switch SW.

  The main battery 12 is a high-voltage power supply for a motor that drives drive wheels (not shown), and the output is about 300V. The auxiliary battery 15 is a power source such as a headlight and a wiper motor (not shown), and supplies power to the DC / DC converter 11 when power from the main battery 12 is not supplied to the DC / DC converter 11. It has become. The auxiliary battery 15 is also used as a power source for the converter control unit 17 of the DC / DC converter 11.

  The primary side of the main circuit 14 is provided with a noise filter 18, a switching unit 19 that converts direct current to alternating current, and a current detection unit 20 that detects an output current of the switching unit 19, and a rectifying unit 21 on the secondary side. And a noise filter 22 are provided. The noise filter 22 is connected to the output terminal 14a via the diode 23. The switching unit 19 includes a switching element (not shown) that is switching-controlled by a control signal from the converter control unit 17. The transformer 13 insulates the primary side to which a high-voltage current is input from the secondary side to which a low-voltage current is output. The transformer 13 steps down the high voltage (about 300V) input from the main battery 12 to the low voltage (about 45V).

  The backup circuit 16 includes a switching element 24 constituting a booster circuit, and is connected to the output terminal 14a via a diode 25. In the switching element 24, a switching semiconductor chip 26 is built in a case 27. A temperature sensor 28 is provided on the surface of the case 27 as temperature detecting means for detecting the surface temperature of the case 27. As the temperature sensor 28, for example, a known configuration using a thermistor or a diode is used.

  When the DC / DC converter 11 cannot receive power supply from the main battery 12, the backup circuit 16 is connected to the auxiliary battery 15 in a state where the switch SW is held in the ON state by the control signal from the converter control unit 17. Power is input and boosted to a predetermined voltage and output. The switching element of the switching unit 19 and the switching element 24 of the backup circuit 16 are controlled by the converter control unit 17.

  The converter control unit 17 determines whether or not power can be supplied from the main battery 12 to the DC / DC converter 11 from a main machine controller (not shown) for the motor that drives the drive wheels, that is, the main battery 12 is connected to the DC / DC. It is configured to input a signal indicating whether or not it can be used as a power source for the DC converter 11. Then, when the main battery 12 is not used as a power source for the DC / DC converter 11, control is performed so that a predetermined voltage is output from the backup circuit 16. When the main battery 12 is badly used as the power source of the DC / DC converter 11, when the capacity of the main battery 12 is smaller than a preset value, driving wheels are driven during rapid acceleration, climbing, etc. There are times when a large amount of power needs to be supplied. Further, the converter control unit 17 performs control so that a predetermined voltage is output from the backup circuit 16 even when a failure occurs in the main circuit 14.

  The converter control unit 17 is composed of a microcomputer and functions as a threshold setting unit, a determination unit, and a stop unit. The converter control unit 17 functions as threshold setting means by inputting a detection signal of the temperature sensor 28 before starting the switching of the semiconductor chip 26 and setting a threshold based on the detected temperature. After the switching of the semiconductor chip 26 starts, the converter control unit 17 determines whether the temperature detected by the temperature sensor 28 is equal to or higher than the threshold set by the threshold setting means, so that the temperature of the semiconductor chip 26 needs to be protected. It functions as a determination means for determining whether or not the temperature is to be applied. The converter control unit 17 functions as a stopping unit by stopping the operation of the semiconductor chip 26 when the determining unit determines that the detected temperature is equal to or higher than the threshold value.

  The converter control unit 17 sets the threshold based on the surface temperature of the case 27 when the switching of the semiconductor chip 26 is started and the difference between the chip temperature obtained after the start of switching and the case surface temperature obtained in advance. . More specifically, in the memory (not shown) of the converter control unit 17, the amount of increase in the semiconductor chip temperature and the case surface temperature from when the switching of the semiconductor chip 26 is started in the maximum load state as shown in FIG. A map showing changes and changes with time of the difference between the semiconductor chip temperature and the case surface temperature is stored. A plurality of maps in which the temperature at the start of switching of the semiconductor chip 26 is changed are stored as a map. FIG. 2 is a map when the temperature at the start of switching is 80.degree. The converter control unit 17 sets a case surface temperature corresponding to the upper limit value of the chip temperature as a threshold using a map from the temperature at the start of switching.

Next, the operation of the apparatus configured as described above will be described.
The converter control unit 17 receives the command that the main battery 12 should not be used as the power source of the DC / DC converter 11 from the main unit control device, and the main battery 12 except when a failure occurs in the main circuit 14. Is used as a power source to drive and control the DC / DC converter 11. That is, the converter control unit 17 controls the switching unit 19 in a state where power can be supplied from the main battery 12 to the main circuit 14. An alternating current is generated in the primary winding of the transformer 13 by switching of the switching element of the switching unit 19 and an alternating current of a predetermined voltage is generated in the secondary winding. Then, the alternating current generated in the secondary winding is rectified by the rectifier 21 to become a direct current, and is output from the output terminal 14a. The DC voltage output from the output terminal 14a is used as auxiliary power.

  When receiving a command signal from the main engine control device not to use the main battery 12 as a power source for the DC / DC converter 11, or when a failure occurs in the main circuit 14, the converter control unit 17 supplies the main power source. Control is performed so that the drive of the DC / DC converter 11 is continued by switching from the battery 12 to the auxiliary battery 15. The converter control unit 17 drives and controls the backup circuit 16 after switching the switch SW to the ON state. Then, the voltage of the auxiliary battery 15 is boosted to a predetermined voltage by the backup circuit 16 and is output from the output terminal 14a.

  The drive control of the backup circuit 16, that is, the switching control of the semiconductor chip 26 is performed according to the flowchart of FIG. First, in step S1, the case surface temperature is measured (measured) and a threshold value is set. The case surface temperature is measured by inputting the detection signal of the temperature sensor 28 and obtaining the temperature from the value. Then, a threshold is set from the measured case surface temperature and the map. Table 1 shows the relationship between the temperature at the start of switching of the semiconductor chip 26 and the case surface temperature when the semiconductor chip 26 reaches a chip temperature upper limit of 150 ° C.

次にステップＳ２で半導体チップ２６のスイッチングが開始され、ステップＳ３で動作中、即ちバックアップ回路１６から所定の電圧が出力される状態になる。次にステップＳ４に進み、ケース表面温度の計測が行われ、ステップＳ５で計測された温度が閾値以上か否かの判断が行われる。計測された温度が閾値より小さいと判断されれば、即ち閾値未満であればステップＳ３に戻り、半導体チップ２６のスイッチング制御が継続されてステップＳ３，Ｓ４，Ｓ５が繰り返される。そして、バックアップ回路１６から所定の電圧が出力される状態が継続される。

Next, switching of the semiconductor chip 26 is started in step S2, and in operation in step S3, that is, a predetermined voltage is output from the backup circuit 16. Next, it progresses to step S4, measurement of case surface temperature is performed, and it is judged whether the temperature measured by step S5 is more than a threshold value. If it is determined that the measured temperature is lower than the threshold value, that is, if it is lower than the threshold value, the process returns to step S3, the switching control of the semiconductor chip 26 is continued, and steps S3, S4, and S5 are repeated. Then, the state where a predetermined voltage is output from the backup circuit 16 is continued.

  On the other hand, if it is determined that the temperature measured in step S5 is equal to or higher than the threshold value, the process proceeds to step S6, where switching of the semiconductor chip 26 is stopped, and the semiconductor chip 26 is prevented from being switched in a state of the upper limit standard temperature or higher. The overheat protection of the backup circuit 16 is performed.

  As shown in Table 1, the case surface temperature when the semiconductor chip 26 reaches a chip temperature upper limit of 150 ° C., that is, the threshold value, varies depending on the temperature at which the semiconductor chip 26 starts switching. Since there is no difference between the chip temperature and the case temperature at the start of switching, the case surface temperature at the start of switching does not reach 150 ° C instantaneously even when switching is started in a non-operating state where the ambient temperature exceeds 90 ° C. . Therefore, if the threshold is set with a margin for the time for the chip temperature to reach the upper limit from the start of switching, the chip temperature can be prevented from exceeding the upper limit even when switching is started at 90 ° C. or higher. it can.

According to this embodiment, the following effects can be obtained.
(1) In the overheat protection device, the switching semiconductor chip 26 is built in the case 27, and the switching element 24 used in the state where the temperature of the semiconductor chip 26 at the start of switching and the surface temperature of the case 27 are the same. Applied. Therefore, the accuracy of estimating the temperature of the semiconductor chip 26 from the surface temperature of the case 27 is increased, and overheating protection of the switching element in which switching is started in the state where the chip temperature and the case temperature are the same can be performed more accurately than in the past. In addition, the operation can be started even when the ambient temperature is higher than that in the prior art. Also, since there is no difference between the chip temperature and the case temperature at the start of switching, the chip temperature will exceed the upper limit even if switching is started from a non-operating state where the case surface temperature at the start of switching exceeds the ambient temperature of 90 ° C Can be prevented.

  (2) The overheat protection device includes a temperature sensor 28 that detects the surface temperature of the case 27, a threshold setting unit that sets a threshold based on the detected temperature at the start of switching of the semiconductor chip 26 detected by the temperature sensor 28, And determining means for determining whether or not the temperature of the semiconductor chip 26 is equal to or higher than a temperature corresponding to the threshold value after switching of the semiconductor chip 26 is started. Then, after the switching is started, the determination unit includes a stop unit that stops the operation of the semiconductor chip 26 when it is determined that the temperature of the semiconductor chip 26 is equal to or higher than the temperature corresponding to the threshold value. Therefore, overheating protection of the switching element in which switching is started in a state where the chip temperature and the case temperature are the same can be performed with higher accuracy than before, and the operation can be started even when the ambient temperature is higher than before.

  (3) The temperature detected by the temperature sensor 28 is used to determine whether the temperature of the semiconductor chip 26 is equal to or higher than the temperature corresponding to the threshold value after the start of switching. As a method of determining whether or not the temperature of the semiconductor chip 26 is equal to or higher than the temperature corresponding to the threshold value, there is a method of using an elapsed time from the start of switching. However, the temperature detected by the temperature sensor 28 can accurately reflect the temperature of the semiconductor chip 26.

  (4) The switching element 24 is used in the backup circuit 16. Therefore, the overheat protection of the switching element 24 of the backup circuit 16 can be performed with higher accuracy, and the operation can be started even when the ambient temperature at the start of switching is higher than 90 ° C.

  (5) The threshold setting means sets the threshold based on the case surface temperature when switching of the semiconductor chip 26 is started and the difference between the chip temperature obtained after the start of switching and the case surface temperature. Therefore, overheat protection is performed more appropriately.

The embodiment is not limited to the above, and may be embodied as follows, for example.
The temperature sensor 28 is not provided at a position where the surface temperature of the case 27 is directly detected, but is provided at a position where an ambient temperature equivalent to the surface temperature of the case 27 is detected, or a constant relationship with the surface temperature of the case 27. It may be provided in a certain place.

  ○ After starting the switching of the semiconductor chip 26, the configuration for determining whether or not the temperature of the semiconductor chip 26 is equal to or higher than the temperature corresponding to the threshold value is the surface temperature of the case 27 when the temperature of the semiconductor chip 26 becomes the upper limit standard. The configuration is not limited to the configuration in which the temperature detected by the temperature sensor 28 is compared with the threshold value. For example, the time until the temperature of the semiconductor chip 26 reaches the upper limit specification from the temperature at the start of switching is set as a threshold value, and the judgment means sets the chip temperature to the upper limit specification when the elapsed time from the start of switching reaches the threshold value. The operation of the semiconductor chip 26 may be stopped (switching is stopped).

  Instead of storing the map as shown in FIG. 2 in the memory of the converter control unit 17 for a plurality of cases with different case temperatures at the start of switching, the temperature at the start of switching and the semiconductor chip 26 after the start of switching You may memorize | store the map which shows the relationship with case surface temperature when it becomes an upper limit specification.

○ The upper limit of the semiconductor chip 26 is not limited to 150 ° C.
The temperature detection means is not limited to the temperature sensor 28 using a thermistor or a diode.
The backup circuit 16 may be driven only when the main circuit 14 fails. In this case, instead of using the backup battery 16 as the auxiliary battery 15, the main battery 12 may be used as the backup circuit 16, and a step-down circuit may be provided in place of the step-up circuit.

  The backup circuit 16 is not limited to a component constituting a part of a DC / DC converter as a power supply device that supplies power to a plurality of auxiliary machines of a hybrid vehicle. For example, it may be embodied in a power supply device for an electric device used in a factory or the like.

  ○ The overheat protection device is a switching element in which the semiconductor chip 26 for switching is built in the case 27 and the temperature of the semiconductor chip 26 at the start of switching and the surface temperature of the case 27 are used in the same state. The present invention is not limited to the overheat protection of the switching element used in the backup circuit 16. For example, it may be applied for overheating protection of a switching element that is driven for a predetermined time from the start of driving and is used in a state where the temperature of the semiconductor chip becomes the same as the case surface temperature after the driving is stopped. .

The following technical idea (invention) can be understood from the embodiment.
(1) In the invention according to any one of claims 1 to 3, when the threshold value setting means starts switching from a detection temperature at the time of starting switching of the semiconductor chip, the temperature of the semiconductor chip Is set to the surface temperature of the case when the upper limit is reached.

  (2) In the invention according to claim 1 or 2, when the threshold value setting means starts switching from a detected temperature at the start of switching of the semiconductor chip, the temperature of the semiconductor chip reaches an upper limit standard. The threshold is set to the elapsed time until.

The circuit diagram of one embodiment. The graph which shows the time-dependent change of the raise amount of the semiconductor chip temperature and case surface temperature from the time of the start of switching of a semiconductor chip in a maximum load state, and the time-dependent change of the difference of semiconductor chip temperature and case surface temperature. The flowchart which shows the effect | action of an overheat protection apparatus. The block diagram of a prior art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 16 ... Backup circuit, 17 ... Converter control part as threshold setting means, judgment means, and stop means, 24 ... Switching element, 26 ... Semiconductor chip, 27 ... Case, 28 ... Temperature sensor as temperature detection means.

Claims (3)

A semiconductor chip for switching is built in the case, and the switching element overheat protection device is used in the same state as the temperature of the semiconductor chip and the surface temperature of the case at the start of switching,
Temperature detecting means capable of detecting the surface temperature of the case;
Threshold setting means for setting a threshold based on a detected temperature at the start of switching of the semiconductor chip detected by the temperature detecting means;
Determining means for determining whether the temperature of the semiconductor chip is equal to or higher than a temperature corresponding to the threshold set by the threshold setting means after the semiconductor chip starts switching;
An overheat protection device for a switching element, comprising: a stopping unit that stops the operation of the semiconductor chip when the determining unit determines that the temperature of the semiconductor chip is equal to or higher than a temperature corresponding to the threshold value.   The overheat protection device for a switching element according to claim 1, wherein the switching element is used in a backup circuit.   The threshold value setting means sets the threshold value based on a case surface temperature when switching of the semiconductor chip is started and a difference between a chip temperature obtained after the start of switching and a case surface temperature obtained in advance. The overheat protection apparatus of the switching element of Claim 1 or Claim 2.

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