JP2011124269A - Power semiconductor device for igniter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power semiconductor device for an igniter that protects a semiconductor switching element at an abnormally high temperature but does not cause an erroneous ignition at an improper timing accompanying current interruption.
A semiconductor switching element 4 for energizing / cutting off a primary current of an ignition coil 6, an integrated circuit 3 for driving and controlling the semiconductor switching element, and a temperature detecting element 43 for detecting an operating temperature of the semiconductor switching element 4. In the igniter power semiconductor device 5 having the above, when the temperature detected by the temperature sensing element 43 is equal to or higher than a predetermined set temperature, the current flowing through the semiconductor switching element 4 is lower than that during normal operation according to the detected temperature With overheat protection circuit to limit the value.
[Selection] Figure 1

Description

  The present invention relates to an igniter power semiconductor device having an overheat protection function for protecting a semiconductor switching element at an abnormally high temperature in an ignition system for an internal combustion engine.

  An ignition system (ignition system) for an internal combustion engine such as an automobile engine generates an ignition coil (inductive load), a semiconductor switching element for driving the ignition coil, and a control circuit element (semiconductor integrated circuit) for generating a high voltage to be applied to a spark plug. ) And a so-called igniter, and an engine control unit (ECU) including a computer. In many cases, in order to protect the semiconductor switching element when abnormal heat generation occurs during its operation, an overheat protection function that detects this abnormal heat generation and forcibly cuts off the current flowing through the semiconductor switching element is installed. (For example, refer to Patent Document 1).

  Since the overheat protection function is an operation based on self-protection of the power semiconductor device, the cutoff timing is performed regardless of the ignition signal timing by the ECU. Therefore, ignition at an inappropriate timing in the ignition sequence may occur due to the shut-off operation by the overheat protection function, and problems such as engine backfire and knocking may occur.

  As a countermeasure for the above problem, a method of softly interrupting the current so as not to cause ignition at the timing of the interrupting operation, that is, the interrupting speed of the current flowing through the primary coil of the ignition coil is set so as not to induce arc discharge in the spark plug. Various methods for preventing unnecessary ignition operations have been proposed as a gradual method. (For example, see Patent Document 2 and Patent Document 3)

JP-A-8-338350 JP 2001-248529 A JP 2008-45514

  The overheat protection function of the conventional power semiconductor device for igniter is to cut off the current flowing through the semiconductor switching element softly so as not to induce arc discharge in the spark plug when the temperature becomes abnormally high. The shut-off state is maintained while the shut-off operation is started and the device temperature does not decrease thereafter. Therefore, at the same time as overheating detection, there is a problem that the engine is completely stopped regardless of the control signal on the ECU side and the state is maintained. This problem is not the best solution from the viewpoint of fail-safety in automobiles. In addition, normally, a hysteresis is provided in the comparator for overheating judgment to prevent malfunction, so that it does not recover unless it returns to a temperature lower than the temperature at which it was shut off, so that the engine can be restarted It takes a considerable amount of time.

  Further, in order to realize soft interruption so as not to induce arc discharge in the spark plug, it is necessary to provide a circuit for generating a time constant of about 10 m to 100 msec. When such a circuit is formed on a semiconductor integrated circuit, there are problems such as an increase in chip size and an increase in man-hours. On the other hand, even when some of the circuits are formed outside the semiconductor integrated circuit, there is a problem that the cost of the power semiconductor device increases due to an increase in the number of components.

  The present invention has been made to solve the above-described problems. In the case of an abnormally high temperature, the semiconductor switching element is blocked at a timing other than the ignition signal timing on the ECU side while protecting the igniter power semiconductor device. Therefore, an object of the present invention is to obtain an igniter power semiconductor device that can prevent ignition at an inappropriate timing.

  In the igniter power semiconductor device according to the present invention, a semiconductor switching element for energizing / cutting off a primary side current of an ignition coil, an integrated circuit for driving and controlling the semiconductor switching element, and an operating temperature of the semiconductor switching element are detected. An integrated power circuit device for an igniter having a temperature sensing element that, when the temperature detected by the temperature sensing element is equal to or higher than a predetermined set temperature, flows to the semiconductor switching element according to the detected temperature And an overheat protection circuit that limits the current to a value lower than that during normal operation.

  By limiting the current of the semiconductor switching element to a value lower than that during normal operation when the temperature is abnormally high, Joule loss of the semiconductor switching element can be reduced and protected. In addition, basically, since there is no complete cutoff operation other than the ignition signal timing of the ECU, there is no erroneous ignition at an inappropriate timing, and a soft current cutoff circuit becomes unnecessary. Furthermore, since the shut-off operation is not actively performed, the current of the semiconductor switching element is only limited to a low level and the engine is not stopped immediately after detection of overheating, so that there is a time margin for performing appropriate measures on the ECU side.

It is a circuit diagram explaining the structure of Example 1 of this invention. It is a timing chart explaining the structure of Example 1 of this invention. It is a graph which shows the relationship between the reverse direction saturation current of the Schottky barrier diode used as a temperature sensing element in Examples 1-4 of this invention, and temperature. In Examples 1-4 of this invention, it is a graph which shows the relationship between the current limiting value applied to a semiconductor switching element, and temperature. It is a circuit diagram explaining the structure of Example 2 of this invention. It is a circuit diagram explaining the structure of Example 3 of this invention. It is a circuit diagram explaining the structure of Example 4 of this invention.

  FIG. 1 shows an embodiment of an ignition system according to the present invention. In the ignition system of FIG. 1, the ignition coil 6 is connected to a power source Vbat such as a battery at one end of a primary coil 61 and to the igniter power semiconductor device 5 at the other end. Similarly, one end of the secondary coil 62 is connected to the power source Vbat, and the other end is connected to a spark plug 7 whose one end is grounded. Further, the ECU 1 outputs a control input signal for driving the semiconductor switching element 41 to the igniter power semiconductor device.

  Among them, the igniter power semiconductor device 5 drives and controls the IGBT 41 in accordance with the semiconductor switching element 4 including the IGBT 41 for energizing / cutting off the current flowing through the primary coil 61, the control signal from the ECU 1, and other operating conditions. The integrated circuit 3 is provided.

  The IGBT 41, which is a main component of the semiconductor switching element 4, has a current proportional to (for example, about 1/1000) of the collector current Ic in addition to a common collector, emitter, and gate as electrode terminals. The one having a sense emitter through which the current flows is adopted. In addition, a Zener diode 42 for surge voltage protection is connected in the reverse direction between the collector and the gate.

  Further, a Schottky barrier diode 43 is provided on the same substrate as a temperature sensitive element for detecting the temperature of the semiconductor switching element 4. The Schottky barrier diode 43 has an anode connected to the emitter terminal of the IGBT 41 and a cathode connected to a reference side of a current mirror circuit in the integrated circuit 3 described later.

  Next, the function of the integrated circuit 3 and the ignition operation of the entire ignition system will be described with reference to the timing chart of FIG.

  The high-level control input signal applied from the ECU 1 to the input terminal of the integrated circuit 3 at time t1 is shaped by the Schmitt trigger circuit 11, and then turns off the first PchMOS 12. As a result, the first current mirror circuit composed of the second PchMOS 17 and the third PchMOS 18 operates, and the gate current of the IGBT 41 is generated by energizing the first resistor 23 with the output current Ig2.

  The reference current value Ig1 of the first current mirror circuit is a current obtained by subtracting an output current value If2 of a current limiting circuit, which will be described later, and an output current Is2 of an overheat protection circuit, from the output current value Ib1 of the constant current source 19. Value. With respect to the reference side current Ig1, a current Ig2 corresponding to the mirror ratio of the first current mirror circuit becomes an output current.

  Here, a collector current Ic as shown in FIG. 2 flows through the primary coil 61 and the IGBT 41 according to a time constant determined by the inductance and wiring resistance of the primary coil 61.

  Next, when a low level control input signal is applied from the ECU 1 at time t2, the first PchMOS 12 is turned on to stop the first current mirror circuit, and the charge accumulated in the gate of the IGBT 41 is Since the first resistor 23 is discharged in a very short time, the IGBT 41 is cut off.

  At this time, the primary side coil 61 generates a high voltage of about 500 V at the collector terminal of the IGBT 41 in a direction in which the current that has been flowing so far continues to flow. This voltage is boosted to 30 kV according to the winding ratio of the ignition coil 6, and arc discharge is generated in the spark plug 7 connected to the secondary coil 62.

  Next, a case where a high level control input signal that is a relatively long energization time is applied from the ECU 1 at time t3 will be described.

  Similar to the above description, the collector current Ic gradually increases from time t3 by the application of the high-level control input signal from the ECU 1, but in order to prevent the winding of the ignition coil 6 and the magnetic saturation of the transformer. The current limit value is set so that the collector current Ic does not exceed a certain value.

  The limitation of the collector current Ic is realized by the following mechanism. The sense current Ies of the IGBT 41 is passed through the second resistor 24 in the integrated circuit 3, and a voltage corresponding to the collector current Ic of the IGBT 41 is generated in the second resistor 24. This voltage is compared with the voltage Vref1 of the first reference voltage source 22 by the amplifier 21, and a current If1 corresponding to the difference is output by the VI conversion circuit 20. The current If1 is output as a current limiting signal If2 by the second current mirror circuit constituted by the fourth PchMOS 13 and the fifth PchMOS 14 according to the mirror ratio. Since the current limit signal If2 works to reduce the current Ig2 that generates the gate drive voltage of the IGBT 41, the gate voltage decreases and prevents the collector current Ic from increasing. In other words, the collector current Ic is limited to a predetermined constant value because the entire system operates so as to perform a negative feedback operation.

  At time t4, when the collector current Ic reaches the current limit value, the gate voltage of the IGBT 41 has decreased and the pentode is operating. That is, the collector voltage is not sufficiently lowered in the state where the collector current Ic is flowing, and the joule loss is generated in the IGBT 41.

  Since the allowable loss of the IGBT 41 decreases as the operating temperature increases, an overheat protection function that suppresses the Joule loss according to the temperature is required to protect the IGBT 41. The mechanism of the overheat protection function will be described below.

  The cathode side of the Schottky barrier diode 43 mounted on the semiconductor switching element 4 is connected to the reference side of the third current mirror circuit composed of the sixth PchMOS 15 and the seventh PchMOS 15 in the integrated circuit 3. Further, the output current Is2 of the third current mirror circuit works in the direction of reducing the current Ig2 that generates the gate drive voltage of the IGBT 41, as in the above-described current limiting function.

  Here, the reverse saturation current Is of the Schottky barrier diode rises rapidly in the vicinity of over about 170 ° C. as shown in the temperature characteristic graph shown in FIG.

  Therefore, when the operating temperature exceeds about 170 ° C., the gate current is reduced by the third current mirror circuit composed of the Schottky barrier diode 43, the sixth PchMOS 15 and the seventh PchMOS 16 to reduce the collector current Ic. Therefore, the overheat protection function for suppressing the Joule loss of the IGBT 41 is realized.

  The above mechanism is common to the current limiting function in that the current Ig2 that generates the gate drive voltage is reduced. In other words, the overheat protection function is nothing but a function that lowers the current limit value from that during normal operation when the operating temperature is about 170 ° C. or higher as shown in FIG.

  The overheat protection function in the first embodiment only lowers the collector current limit value of the IGBT 41, and does not actively shut down the IGBT 41. That is, there is no shut-off at a timing unintended by the ECU 1, and erroneous ignition of the spark plug 7 can be prevented without installing a separate soft shut-off function.

  If the operating temperature continues to rise, the current limit value will continue to drop and eventually will not be able to supply enough energy to arc discharge the spark plug 7, but the operating speed of the ECU 1 is generally much faster than the operating temperature rises. Therefore, since there is a time margin from when the overheat protection starts to operate until an actual misfire occurs, the ECU 1 detects that the misfire has occurred due to the overheat protection, and has enough time to take appropriate measures.

  FIG. 5 shows a second embodiment of the igniter power semiconductor device according to the present invention. In the drawings, components having the same function are denoted by the same reference numerals, and redundant description is omitted.

  The second embodiment is characterized in that the Schottky barrier diode mounted on the semiconductor switching element 4 in the first embodiment is mounted in the integrated circuit 3. In the igniter power semiconductor device 5, since the semiconductor switching element 4 and the integrated circuit 3 are arranged in the vicinity on the same conductor substrate, the thermal coupling between them is extremely good. Therefore, the same effect can be obtained without mounting a temperature sensitive element on the semiconductor switching element 4.

  It is more desirable that the Schottky barrier diode 25 in the integrated circuit 3 is mounted at a position close to the semiconductor switching element 4 in the layout, for example, near a side facing the switching element 4 of the integrated circuit 3.

  In this embodiment, the connection lines and pads of the Schottky barrier diode 43 required in the first embodiment can be reduced, the layout pattern efficiency of the semiconductor switching element 4 can be increased, and the area can be arranged efficiently. The device 5 can be realized in a small size and at a low cost.

  The fact that the Schottky barrier diode 25 which is a temperature sensitive element is mounted in the integrated circuit 3 can be positively utilized. For example, a diode used for generating the constant current source 19 is not a normal PN junction type, but a Schottky barrier diode is used, so that the temperature characteristic of the constant current source is the temperature characteristic of the Schottky barrier diode 25 which is a temperature sensitive element. You may make it match.

  By providing the constant current source 19 with temperature characteristics, it is possible to make the current limit value lowering characteristics during overheat protection sharper together with the temperature characteristics of the temperature sensing element. In the same integrated circuit 3, the characteristic matching between the elements can be made extremely high, so that the temperature characteristics of the constant current source 19 and the Schottky barrier diode 25 which is a temperature sensitive element can be matched with high accuracy.

  FIG. 6 shows a third embodiment of the power semiconductor device for an igniter according to the present invention. In the first and second embodiments, there may be a case where a desired reduction characteristic is not obtained for the current limit value at the time of overheat protection due to the manufacturing process variation of the reverse saturation current of the Schottky barrier diode. By adjusting this variation with the external connection terminals, it is possible to improve the yield of the product, and it is also possible to adjust the current limit value attenuation sensitivity according to the product application.

  In the circuit example shown in FIG. 6, three temperature sensing element selection circuits S1, S2, and S3 having different output current values are provided to enable / disable each temperature sensing element output from the outside of the igniter power semiconductor device 5. You can choose.

  A Schottky barrier diode 25 is built in each temperature sensing element selection circuit of S1 to S3, and binary weighting is given to the size of each diode (for example, if S1 is size 1, S2 is size 2, S3 is Size 4). Further, by grounding or opening the external terminal, the eighth PchMOS 26 is turned on or off, and each temperature sensing element selection circuit is validated / invalidated.

  Thereby, it is possible to select the size of the Schottky barrier diode from eight types from 0 to 7 by the combination of the temperature sensitive elements S1 to S3. The selection of the temperature sensitive element may be set from the outside of the igniter power semiconductor device 5 as in this embodiment, or if adjustment is performed only within the manufacturing process, no terminal is provided outside. The validity / invalidity of each temperature sensing element may be selected based on the presence / absence of wire bonding between the pads S1 to S3 provided on the integrated circuit 3 and the ground terminal.

  FIG. 7 shows a fourth embodiment of the power semiconductor device for an igniter according to the present invention. As described in the first embodiment, when the operating temperature rises and the overheat protection starts to operate, an appropriate notification is transmitted to the ECU 1, the control signal on-time table data is reviewed, and the engine output is reduced. It is desirable to take a feedback action.

  Therefore, in this embodiment, the overheat protection operation state output means 10 is provided in the integrated circuit 3. A ninth PchMOS 40 is connected to the output side of the third current mirror circuit for detecting the reverse saturation current Is1 of the Schottky barrier diode 25 which is a temperature sensing element, and the output current Is3 is passed through the third resistor 43. The voltage generated in the third resistor 43 and the voltage Vref2 of the second reference voltage source 42 are compared by the comparator 41, and the output is output to the outside of the igniter power semiconductor device 5 so that it can be monitored by the ECU1. .

  With the igniter power semiconductor device 5 of the fourth embodiment configured as described above, the ECU 1 can grasp from time to time whether or not the overheat protection operation is currently performed, based on the output of the comparator 41. It is possible to perform various feedback procedures.

  3. Integrated circuit 4. 4. Semiconductor switching element 5. Power semiconductor device for igniter Ignition coil 10. Error output circuit 15. Sixth PchMOS 16. Seventh PchMOS 25,43 Schottky barrier diode

Claims (6)

A semiconductor switching element that energizes / cuts off the primary side current of the ignition coil; and
An integrated circuit for driving and controlling the semiconductor switching element;
A temperature sensing element for detecting a temperature during operation of the semiconductor switching element;
An igniter power semiconductor device comprising:
The integrated circuit includes overheat protection means for limiting a current flowing through the semiconductor switching element to a value lower than that during normal operation according to the detected temperature when the temperature detected by the temperature detecting element is equal to or higher than a predetermined set temperature. ,
An igniter power semiconductor device comprising: The igniter power semiconductor device according to claim 1, wherein the temperature sensitive element is mounted on the semiconductor switching element. The igniter power semiconductor device according to claim 1, wherein the temperature sensitive element is mounted on the integrated circuit. The igniter power semiconductor device according to claim 1, wherein the temperature-sensitive element includes a Schottky barrier diode. 5. The power semiconductor device for an igniter according to claim 1, wherein the temperature sensitive element is capable of adjusting temperature characteristics from the outside. 5. The igniter power semiconductor device according to claim 1, further comprising an overheat protection operation state output unit configured to output a signal indicating that a current drop is performed by the overheat protection circuit. 6. .

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