Abstract:
In aspects of the invention, there is provided an igniting semiconductor device that can prevent burning of an IGBT or ignition coil, and erroneous ignition, even when reducing the size of a capacitor that generates a self-interrupting circuit time constant. In some aspects, a semiconductor device of the invention is configured of an IGBT and a current control circuit. The current control circuit can be configured of a first series circuit wherein an IGBT and a sense resistor are connected in series, a drive signal control circuit, and a self-interrupting circuit. At a time of abnormal operation, the self-interrupting circuit can output a voltage whose amplitude temporally drops in stages toward 0V to the drive signal control circuit. The drive signal control circuit can control the amplitude of a drive control signal so that the voltage across the sense resistor is equivalent to the output voltage of the self-interrupting circuit.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     Embodiments of the invention relate to semiconductor devices used in automobile internal combustion engine ignition devices, as well as other devices. 
     2. Related Art 
       FIG. 17  shows an example of a configuration of a heretofore known general internal combustion engine ignition semiconductor device using an insulated gate bipolar transistor (hereafter referred to as an IGBT) as a power semiconductor element. See, for example, Japanese Patent Application No. JP-A-2012-36848. 
     An ignition device shown in  FIG. 17  is configured of an engine control unit (hereafter referred to as an ECU)  1 , a semiconductor device  5 , and an ignition unit  7 . 
     The ignition device shown in  FIG. 17  is such that, on an abnormal condition being detected, a self-interrupt signal Vsd is emitted from a self-interrupt signal source  10 , a self-interrupting circuit  33  operates, and a collector current Ic of an IGBT Tr 2  is interrupted. An abnormal condition is a condition such that there is a danger of damage such as burning occurring in an ignition coil L or the semiconductor device  5 , such condition being, for example, a turn-on signal output from the ECU  1  being longer than a predetermined time (for example, 10 ms or longer), or the temperature of the semiconductor device  5  being higher than a specified value (for example, 180° C. or higher). 
     However, when the collector current Ic is abruptly interrupted using this kind of current control function or self-interrupt function, fluctuation is caused in the collector current Ic, and there is a problem in that erroneous ignition of a spark plug  4  is caused, and the engine is damaged. 
     Technology whereby the collector current Ic is gently reduced being known as a countermeasure to erroneous ignition caused by the fluctuation of the collector current Ic, a method whereby a soft shut-off circuit is provided, and a gentle reduction time set, is disclosed in Japanese Patent Application No. JP-A-2008-45514. Also, a method whereby an integrated circuit formed of a diode and capacitor is provided, and a collector current Ic gentle reduction time set, is disclosed in Japanese Patent Application No. JP-A-2006-37822. 
     Meanwhile, a current control circuit  6  shown in  FIG. 17  includes a self-interrupting circuit  33  shown in  FIG. 18 . The self-interrupting circuit  33  is configured of a bias circuit wherein a DepMOSFET (Depression Metal-Oxide Semiconductor Field-Effect Transistor, hereafter referred to as a DepMOS) Tr 7  and a MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor, hereafter referred to as a MOS) Tr 8  are connected in series with a common gate, a MOS Tr 9  configuring a current mirror circuit with the MOS Tr 8 , a MOS Tr 4  connected in series with the MOS Tr 9 , an inverter NOT 1  connected to the gate of the MOS Tr 4 , and a capacitor C 1  connected in parallel to the MOS Tr 9 . 
     The MOS Tr 4  is controlled on and off by the self-interrupt signal Vsd, being in an on-state at a time of no al operation and an off-state at a time of abnormal operation. Also, by the on-state resistance of the MOS Tr 4  being set sufficiently low in comparison with the on-state resistance of the MOS Tr 9 , the capacitor C 1  is charged at a time of normal operation, and a reference voltage Vref is output as it is, while at a time of abnormal operation, the output voltage gradually drops from Vref to 0V by the capacitor C 1  being discharged via the MOS Tr 9 . 
     An operational amplifier OP 1  detects the difference between a voltage (hereafter referred to as a sense voltage) Vsns across a sense resistor R 1  and the reference voltage Vref, wherein a target value of the collector current (the current caused to flow through a primary coil L 1 ) Ic is converted into voltage, the two voltages having been level shifted via level shift circuits  9  and  15  respectively. The on-state resistance of the MOS Tr 3  is controlled by the gate voltage of the MOS Tr 3  being controlled in accordance with the result of the detection. 
     The ignition semiconductor device shown in  FIG. 17  is such that, in order to reduce the capacitance C 1  without changing a temporal amount of change (hereafter called the inclination) dlc/dt in the collector current, it is sufficient to reduce a drain current Id of the MOS Tr 9 . However, as the drain current Id is an extremely low current in the order of nA, the more the drain current Id is reduced, the more difficult it becomes to maintain a constant current. Consequently, reducing the drain current Id is not desirable. Also, as erroneous ignition occurs when the inclination dlc/dt of the collector current is too large, while the IGBT or ignition coil L is burned when the inclination dlc/dt is too small, there is a demand for a high precision drain current Id control. 
     Thus, as described in the related art, there is a limit to the reduction of capacitance of the self-interrupting circuit capacitor and the accuracy of current control, as well as other shortcomings. 
     SUMMARY OF THE INVENTION 
     Embodiments of the invention address these and other shortcomings. Some embodiments of the invention provide a semiconductor device that can reliably prevent burning of an IGBT ignition coil, and erroneous ignition, even when reducing the capacitance of a self-interrupting circuit capacitor. 
     A semiconductor device according to one aspect of the invention includes a first series circuit wherein a first semiconductor switching element and a sense resistor are connected in series, a second semiconductor switching element connected in parallel to the first series circuit, a drive signal control circuit, into which a drive signal is input, that outputs a drive control signal controlling the first and second semiconductor switching elements, and a self-interrupting circuit connected to the drive signal control circuit, wherein the self-interrupting circuit outputs a predetermined voltage to the drive signal control circuit at a time of normal operation, and outputs a voltage whose amplitude temporally changes in stages to the drive signal control circuit at a time of abnormal operation, and the drive signal control circuit controls so that the amplitude of the drive control signal decreases when the voltage across the sense resistor is higher than the output voltage of the self-interrupting circuit, and controls so that the amplitude of the drive control signal increases when the voltage across the sense resistor is lower than the output voltage of the self-interrupting circuit. 
     In some embodiments, it is possible to temporally change in stages the current amplitude of the second semiconductor switching element by comparing the voltage whose amplitude temporally changes in stages at a time of abnormal operation and the voltage across the sense resistor proportional to the current of the second semiconductor switching element, and controlling the amplitude of the drive control signal. Consequently, as it is possible to change the current of the second semiconductor switching element gently, unlike with an on/off control, it is possible to prevent erroneous ignition. 
     The semiconductor device according to the aspect of the invention can include a self-interrupting circuit includes a second series circuit wherein a third semiconductor switching element and a first capacitor are connected in series, a fourth semiconductor switching element connected in parallel to the first capacitor, and a third series circuit wherein a fifth semiconductor switching element and a second capacitor are connected in series, wherein the second series circuit is connected in parallel to the second capacitor, which outputs the voltage across the second series circuit to the drive signal control circuit, and a voltage of a predetermined value is applied to the third series circuit, and the self-interrupting circuit further includes an abnormality detecting circuit that supplies the voltage of the predetermined value to the second capacitor by the fifth semiconductor switching element being turned on when it is determined that there is normal operation, and interrupts the voltage supplied to the second capacitor by the fifth semiconductor switching element being turned off when it is determined that there is abnormal operation, and an interval generator circuit that exclusively turns the third and fourth semiconductor switching elements on and off at a predetermined interval. 
     According to some embodiments, it is possible to delay the discharge of the second capacitor by lengthening the change cycle of the voltage whose amplitude temporally changes in stages, and thus possible to reduce the capacitance of the second capacitor. 
     Also, in some embodiments, it is possible to prevent burning of the IGBT or ignition coil, and erroneous ignition, by regulating the capacitance of the second capacitor and the predetermined interval. 
     In some embodiments, a self-interrupting circuit is such that an nA order constant current source is unnecessary, and it is thus possible to reliably prevent burning of the IGBT or ignition coil, and erroneous ignition. 
     The semiconductor device according to the aspect of the invention is such that the abnormality detecting circuit determines that there is abnormal operation when the drive signal is input into the drive signal control circuit for a time exceeding a predetermined time. 
     According to some embodiments of the invention, when the drive signal is input into the drive signal control circuit for a time exceeding a predetermined time, the self-interrupting circuit temporally changes the amplitude of the drive control signal in stages, thereby reducing the current of the second semiconductor switching element gently. That is, it is possible to prevent a second semiconductor switching element overcurrent that continues to increase as long as the second semiconductor switching element continues to be in an on-state, and thus possible to prevent burning. 
     The semiconductor device according to the aspect of the invention is such that the abnormality detecting circuit determines that there is abnormal operation when the temperature of a predetermined region exceeds a predetermined temperature. 
     According to some embodiments, the self-interrupting circuit temporally changes the amplitude of the drive control signal in stages when the temperature of the predetermined region exceeds a predetermined temperature, thereby reducing the current of the second semiconductor switching element gently. That is, it is possible to prevent overheating of the predetermined region, and thus possible to prevent accidents including burning. 
     The semiconductor device according to the aspect of the invention is such that the interval generator circuit controls at least one of the turn-on timing or duty of the third semiconductor switching element. 
     According to some embodiments, it is possible to control at least one of the voltage range or duration of one stage of the voltage whose amplitude is temporally changed in stages, and thus possible to control the current of the second semiconductor switching element as desired. For example, by lengthening the turn-on timing cycle, it is possible to lengthen the duration of one stage of the voltage whose amplitude is temporally changed in stages. Also, by reducing the duty, it is possible to reduce the voltage range of one stage of the voltage whose amplitude is temporally changed in stages. That is, it is possible to reliably prevent burning of the IGBT or ignition coil, and erroneous ignition, even when reducing the capacitance of the self-interrupting circuit capacitor. 
     The semiconductor device according to the aspect of the invention is such that the interval generator circuit lengthens the turn-on timing cycle of the third semiconductor switching element further the higher the temperature of a predetermined region. 
     According to some embodiments, it is possible to reduce variation in the amount of change in one stage of the voltage whose amplitude is temporally changed in stages caused by temperature change in a predetermined region. That is, it is possible to control the current of the second semiconductor switching element so that dependency on the temperature of a predetermined region is reduced. 
     The semiconductor device according to the aspect of the invention is such that the interval generator circuit reduces the duty of the third semiconductor switching element further the higher the voltage of the second capacitor. 
     According to some embodiments, the amount of change in one stage of the voltage whose amplitude is temporally changed in stages is such that the duration of the sudden voltage drop when the voltage across the self-interrupting circuit capacitor is high can be reduced, and the voltage range narrowed. That is, as it is possible to obtain a still gentler change in the current of the second semiconductor switching element, it is possible to more reliably prevent erroneous ignition. 
     According to the semiconductor device of the invention, an excellent advantage may be obtained in that it is possible to reliably prevent burning of an IGBT or ignition coil, and erroneous ignition, even when reducing the capacitance of a capacitor generating a self-interrupting circuit time constant. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a configuration of a semiconductor device in accordance with some embodiments of the invention; 
         FIG. 2  is a diagram showing a semiconductor device according to a first embodiment of the invention; 
         FIG. 3  is a diagram showing an example of a circuit configuration of a self-interrupting circuit in accordance with some embodiments of the invention; 
         FIG. 4  is a diagram showing operation waveforms of the semiconductor device according to the first embodiment of the invention; 
         FIG. 5  is a diagram showing operation waveforms of a switched capacitor circuit according to the first embodiment of the invention; 
         FIG. 6  is a diagram showing a semiconductor device according to a second embodiment of the invention; 
         FIG. 7  is a diagram showing circuit configuration examples for a timer circuit and pulse generator circuit in accordance with some embodiments of the invention; 
         FIG. 8  is a diagram showing time charts for the timer circuit and pulse generator circuit according to the invention; 
         FIG. 9  is a diagram showing a semiconductor device according to a third embodiment of the invention; 
         FIG. 10  is a diagram showing a circuit configuration example for a temperature compensation circuit in accordance with some embodiments of the invention; 
         FIG. 11  is a diagram showing temperature characteristics of an overheat detection voltage in accordance with some embodiments of the invention; 
         FIG. 12  is a diagram showing circuit configuration examples for the timer circuit, pulse generator circuit, and temperature compensation circuit in accordance with some embodiments of the invention; 
         FIG. 13  is a diagram showing a voltage control oscillator in accordance with some embodiments of the invention; 
         FIG. 14  is a diagram showing time charts for a tinier circuit and pulse generator circuit according to a fourth embodiment of the invention; 
         FIG. 15  is a diagram showing detailed operation waveforms of a switched capacitor circuit according to the second embodiment of the invention; 
         FIG. 16  is a diagram showing detailed operation waveforms of a switched capacitor circuit according to the fourth embodiment of the invention; 
         FIG. 17  is a diagram showing a configuration of a heretofore known semiconductor device; and 
         FIG. 18  is a diagram showing an example of a circuit configuration of a heretofore known self-interrupting circuit. 
     
    
    
     DETAILED DESCRIPTION 
     Hereafter, referring to the attached drawings, a description will be given of embodiments of the invention. 
     First Embodiment 
       FIG. 2  shows a semiconductor device according to a first embodiment of the invention, wherein portions given the same reference signs as in  FIG. 17  represent the same portions, and the basic configuration is the same as the heretofore known configuration shown in  FIG. 17 . 
     Next, a description will be given of a circuit configuration of the first embodiment. 
     The circuit of the first embodiment of the invention is configured of an ECU  1 , a semiconductor device  5 , and an ignition unit  7 . The semiconductor device  5  has a G terminal, a C terminal, and an E terminal, wherein the G terminal is connected to the ECU  1 , and the C and E terminals are connected to the ignition unit  7 . 
     The semiconductor device  5  is configured of an IGBT Tr 2  and a current control circuit  6 . The current control circuit  6  is configured of a first series circuit wherein an IGBT Tr 1  and a sense resistor R 1  are connected in series, a reference voltage supply  14 , a level shift circuit  15 , a drive signal control circuit  2 , a self-interrupt signal source  10 , and a self-interrupting circuit  3 . The first series circuit is connected in parallel to the IGBT Tr 2 , a connection point of the IGBTs Tr 1  and Tr 2  is connected to the C terminal, and a connection point of the sense resistor R 1  and IGBT Tr 2  is connected to the E terminal. 
     The drive signal control circuit  2  is configured of a second series circuit, wherein one end of a gate resistor R 2  and one end of a MOS Tr 3  are connected in series, and an operational amplifier OP 1 . The other end of the gate resistor R 2  is connected to the G terminal, while the other end of the MOS Tr 3  is connected to the E terminal. An intermediate point of the second series circuit is connected to control terminals of the IGBTs Tr 1  and Tr 2  as an output of the drive signal control circuit  2 . Also, the intermediate point of the second series circuit may also be connected to the control terminals of the IGBTs Tr 1  and Tr 2  via a gate control circuit  8 . The output terminal of the operational amplifier OP 1  is connected to a control terminal of the MOS Tr 3 . The positive side input terminal of the operational amplifier OP 1  is connected via the level shift circuit  15  to an intermediate point of the first series circuit. The negative side input terminal of the operational amplifier OP 1  is connected to the self-interrupting circuit  3 . 
     The ignition unit  7  is configured of an ignition coil L having primary and secondary coils L 1  and L 2 , a fourth series circuit wherein the primary coil L 1  and a battery BAT are connected in series, and a fifth series circuit wherein the secondary coil L 2  and a spark plug  4  are connected in series. The fourth and fifth series circuits are connected in parallel to the second IGBT Tr 2 . 
       FIG. 3  shows the self-interrupting circuit  3  of the invention. The self-interrupting circuit  3  of the invention differs from a heretofore known self-interrupting circuit  33  shown in  FIG. 18  in that a power supply circuit  17  is replaced with a switched capacitor circuit  16 . 
     The self-interrupting circuit  3  is configured of a second series circuit, wherein one end of a MOS Tr 4  and a capacitor C 1  are connected in series, and the switched capacitor circuit  16 . The switched capacitor circuit  16  is configured of a third series circuit, wherein a MOS Tr 5  and a capacitor C 2  are connected in series, and a MOS Tr 6  connected in parallel to the capacitor C 2 . The third series circuit is connected in parallel to the capacitor C 1 . The other end of the MOS Tr 4  is connected via the level shift circuit  15  to the output terminal of the reference voltage supply  14 , while the control terminal of the MOS Tr 4  is connected to the output terminal of the self-interrupt signal source  10 . 
     Next, a description will be given of an operation of the semiconductor device according to the first embodiment. 
     Firstly, a drive signal is output from the ECU  1 , and the IGBTs Tr 1  and Tr 2  are turned on via the drive signal control circuit  2 . At this time, the on-state resistance of the IGBTs Tr 1  and Tr 2  is determined by the gate resistor R 2  of the drive signal control circuit  2 . The drive signal from the ECU  1  also acts at the same time as a power source of the reference voltage supply  14 , level shift circuit  15 , self-interrupting circuit  3 , and operational amplifier OP 1 . 
     At this time, the reference voltage supply  14  generates a reference voltage Vref wherein a target value of a current (a collector current Ic) caused to flow through the primary coil L 1  has been converted into a voltage. The reference voltage Vref is stepped-up by the level shift circuit  15  to a voltage of a level that can operate the operational amplifier OP 1 . The stepped-up reference voltage Vref is applied to the second series circuit of the self-interrupting circuit  3 . 
     Also, a current proportional to the current flowing through the primary coil L 1  flows through the sense resistor R 2 , and a sense voltage Vsns, which is the voltage across the sense resistor  2 , is stepped-up by the level shift circuit  15  to a voltage of a level that can operate the operational amplifier OP 1 . The stepped-up sense voltage Vsns is input into the positive side terminal of the operational amplifier OP 1 . 
     Herein, at a time of normal operation, the MOS Tr 4  is turned on by the signal from the self-interrupt signal source  10 , and the reference voltage Vref is applied directly to the negative terminal of the operational amplifier OP 1 . Together with this, the capacitor C 1  is charged by the reference voltage Vref. 
       FIG. 4  shows operation waveforms of the semiconductor device  5  of the invention. In  FIG. 4 , the collector current of the IGBT Tr 2  is taken to be IC, the rated current of the IGBT Tr 2  is IIim, the gate voltage of the IGBT Tr 2  is VGout, the voltage of the G terminal of the semiconductor device  5  is VG, the threshold value voltage of the IGBT Tr 2  is Vth, the sense voltage is Vsns, and the reference voltage is Vref. 
     When Vref&lt;Vsns, the output voltage of the operational amplifier OP 1  rises, and the on-state resistance of the MOS Tr 3  decreases. Also, when Vref Vsns, the output voltage of the operational amplifier OP 1  drops, and the on-state resistance of the MOS Tr 3  increases. By the amplitude of the IGBT Tr 2  gate voltage VGout being controlled in this way, the collector current Ic is controlled to a predetermined current value (t 1 ). 
     Meanwhile, at a time of abnormal operation, the MOS Tr 4  is turned off by a self-interrupt signal Vsd generated by the self-interrupt signal source  10  (t 2 ), and the reference voltage Vref is interrupted. At this time, the capacitor C 1  is discharged by an operation of the switched capacitor circuit  16 , to be described hereafter, and the voltage applied to the negative terminal of the operational amplifier OP 1  drops in stages from the reference voltage Vref to 0V. Together with this, the sense voltage Vsns caused to track the reference voltage Vref also drops, and the current of the primary coil L 1  gradually decreases to 0 A. Then, when VGout becomes equal to Vth (the threshold value voltage of the IGBT Tr 2 ), the collector current Ic is completely interrupted (t 3 ). 
       FIG. 5  shows operation waveforms of the switched capacitor circuit  16 . In  FIG. 5 , the voltage of the capacitor C 1  is taken to be VC 1 , and the voltage of the capacitor C 2  is VC 2 . As previously described, the switched capacitor circuit  16  is such that the third series circuit is connected in parallel to the capacitor C 1 . Further, a cyclical and exclusive on/off signal is input into the control terminals of the MOSs Tr 5  and Tr 6 . Firstly, during a period for which the MOS Tr 5  is in an on-state and the MOS Tr 6  is in an off-state, the capacitor C 1  is discharged via the third series circuit, and the capacitor C 2  is charged. Next, during a period for which the MOS Tr 5  is in an off-state and the MOS Tr 6  is in an on-state, the capacitor C 2  is discharged via the MOS Tr 6 . 
     As the charging and discharging of the capacitors C 1  and C 2  is repeated every time the on and off-states of the MOSs Tr 5  and Tr 6  are repeated in this way, the voltage of the capacitor C 1  drops in stages, eventually reaching 0V. Herein, the capacitor voltage VC 2 , being the output voltage of the self-interrupting circuit  3 , is the voltage in  FIG. 4  of Vref from t 2  onward shown schematically. 
     By controlling at least one of the cycle or duty of the signals turning the MOSs Tr 5  and Tr 6  on and off, it is possible to control the discharge speed of the capacitor C 1 . Also, as it is sufficient that the self-interrupting circuit  3  can generate a voltage that drops in stages at a time of abnormal operation, the configuration and method thereof are not limited to the switched capacitor circuit  16  of the invention. 
     As the reference voltage supply  14  and level shift circuit  15  are heretofore known technology, a detailed description of the operations thereof will be omitted. Also, an unshown gate control circuit  32  of heretofore known JP-A-2012-36848 may be connected to the intermediate point of the second series circuit, but a detailed description Will be omitted. 
     As the semiconductor device according to the first embodiment of he invention is such that an interruption time from t 2  to t 3  is proportional to capacitor C 1 /(capacitor C 2 ×duty), it is possible, by designing each one as appropriate, to reduce the capacitor capacitance without changing the inclination dlc/dt of the collector current. For example, when the duty is 6.25%, the gently decreasing speed dl/dt does not change when the capacitor C 1  is one-sixteenth of that heretofore known, and the capacitor C 2  is four times the capacilor C 1 . That is, the capacitor capacitance can be reduced to four-sixteenths, that is, one-fourth, of that heretofore known. 
     Second Embodiment 
       FIG. 6  shows a semiconductor device according to a second embodiment of the invention, wherein the basic configuration is the same as that of the first embodiment shown in  FIG. 2 . The circuit of the second embodiment of the invention has a timer circuit  12  and a pulse generator circuit  11  in addition to the circuit configuration of the first embodiment. 
       FIG. 7  shows circuit configuration examples for the timer circuit  12  and pulse generator circuit  11 . The timer circuit  12  is configured of an oscillator  18 , a reset circuit  19 , and TFFs  20  to  29 . The TFFs  20  to  29  are connected in a ten stage series, wherein the output of the previous stage is connected to the input of the next stage. 
     The pulse generator circuit  11  has MOSs Tr 10  to Tr 13  connected to each other in parallel. The pulse generator circuit  11  also has a sixth series circuit, wherein the source of a DepMOS Tr 15  and the drain of the MOS Tr 13  are connected, the MOS Tr 14  are connected. Also, the sixth series circuit and seventh series circuit are connected in parallel, configuring a logical NOT circuit. The gate terminals of the MOSs Tr 10  to Tr 13  are connected to the oscillator  18  and the outputs of the TFFs  20  to  22 . 
     Next, an outline description will be given of an operation of the semiconductor device according to the second embodiment. 
     The timer circuit  12  and pulse generator circuit  11  are driven by the voltage between the G terminal and E terminal, and generate a pulse voltage for exclusively turning the MOSs Tr 5  and Tr 6  of the switched capacitor circuit  16  on and off at a predetermined interval. Intermediate points of the sixth and seventh series circuits form an input and output of the logical NOT circuit, and are input into the MOSs Tr 5  and Tr 6  respectively. 
     Continuing, a detailed description will be given of operations of the timer circuit  12  and pulse generator circuit  11 . 
     The timer circuit  12  is such that the oscillator  18  starts oscillating (for example, a cycle of 19.6 μs and a duty of 50%) on a turn-on signal being input into the G terminal. At the same time, the reset circuit  19  outputs a reset signal for a certain time (for example, 10 μs), resetting the TFFs  20  to  29 , and turning off the output. After the reset signal has stopped, the TFFs output a signal of a cycle twice that of the input signal. Therefore, a TIMER signal, which is the final stage of the TFFs  20  to  29 , has a cycle 1,024 times that of the oscillator  18 . 
     The output signals of the oscillator  18  and TFFs  20  to  22  are input into the gates of the MOSs Tr 10  to Tr 13 , and a pulse signal PULSE 1  turns on the MOS Tr 5  only when all of the signals are in an off-state. Time charts of the output signals of the oscillator  18  and TFFs  20  to  22 , and of the pulse signal PULSE 1 , are shown in FIG.  8 . For example, when the signal of the oscillator  18  has a cycle of 9.8 μs and a duty of 50%, the pulse signal PULSE 1  has a cycle of 78.4μs and a duty of 6.25%. 
     The semiconductor device according to the second embodiment the invention is such that it is possible to determine the cycles of the pulse signals PULSE 1  and PULSE 2  as desired by setting the frequency of the oscillator  18 . Also, by selecting the connection positions of the gates of the MOSs Tr 10  to Tr 13  of the pulse generator circuit  11  and the number of MOSs, it is possible to determine the cycles and duties of the pulse signals PULSE 1  and PULSE 2  as desired. 
     Third Embodiment 
       FIG. 9  shows a semiconductor device according to a third embodiment of the invention, wherein the basic configuration is the same as that of the second embodiment shown in  FIG. 6 . The circuit of the third embodiment of the invention has a temperature compensation circuit  13 , a constant current source  34 , a level shift circuit  35 , and a diode D. in addition to the circuit configuration of the second embodiment. 
       FIG. 10  shows a circuit configuration example for the temperature compensation circuit  13 . The temperature compensation circuit  13  has voltage dividing resistors R 3  to R 5  connected in series between the G terminal and E terminal, and comparators COMP 1  and COMP 2 . An overheat detection voltage is input into the negative side terminals of the comparators COMP 1  and COMP 2 , while voltages V 1  and V 2 , wherein the voltage between the G terminal and E terminal is divided by the voltage dividing resistors R 3  to R 5 , is input into the positive side terminals. Herein, the forward voltage of the diode D, which decreases in proportion to the temperature, is used as the overheat detection voltage. The divided voltage V 1  is the voltage across a series circuit of the voltage dividing resistors R 4  and R 5 , while the divided voltage V 2  is the voltage across the voltage dividing resistor R 5 . In this way, the comparators COMP 1  and COMP 2  compare the overheat detection voltage and the divided voltages V 1  and V 2 , and output the comparison results as TEMP 1  and TEMP 2 . 
       FIG. 11  shows a case wherein, as temperature characteristics of an overheat detection voltage Vt, the overheat detection voltage Vt is equivalent to the divided voltages V 1  and V 2  when the temperature of a predetermined region is T 1  and T 2 , and illustrates the temperature compensation signals TEMP 1  and TEMP 2 . As V1&lt;Vt and V2&lt;Vt when a temperature T of the temperature detection region is such that T−T1, the temperature compensation signals TEMP 1  and TEMP 2  are output as L level signals. As V2&lt;Vt&lt;V1 when the temperature T of the temperature detection region is such that T1&lt;T&lt;T2, the temperature compensation signal TEMP 1  is output as an H level signal, while the temperature compensation signal TEMP 2  is output as an L level signal. As Vt&lt;V1 and Vt&lt;V2 when the temperature T of the temperature detection region is such that T2&lt;T, the temperature compensation signals TEMP 1  and TEMP 2  are output as H level signals. 
     The semiconductor device according to the third embodiment of the invention controls the duty using the temperature compensation signals TEMP 1  and TEMP 2 .  FIG. 12  shows a circuit configuration for the temperature compensation signals TEMP 1  and TEMP 2  to control the duty. 
     As the temperature compensation signals TEMP 1  and TEMP 2  are output as L level signals when the temperature T of the temperature detection region is such that T&lt;T1, the outputs of AND circuits  30  and  31  are at an L level, and an L level signal is constantly applied to MOSs Tr 11  and Tr 12 . That is, the duty is determined by the oscillator  18 . 
     As the temperature compensation signal TEMP 1  is output as an H level signal while the temperature compensation signal TEMP 2  is output as an L level signal when the temperature T of the temperature detection region is such that T1&lt;T&lt;T2, the output of the AND circuit  30  is equivalent to the output of the TFF  20 , while the output of the AND circuit  31  is at an L level. That is, the duty is determined by the oscillator  18  and TFF  20 . 
     As the temperature compensation signals TEMP 1  and TEMP 2  are output as H level signals when the temperature T of the temperature detection region is such that T2&lt;T, the output of the AND circuit  30  is equivalent to the output of the TFF  20 , while the output of the AND circuit  31  is equivalent to the output of the TFF  21 . That is, the duty is determined by the oscillator  18 , the TFF  20 , and the TFF  21 . 
     The semiconductor device according to the third embodiment of the invention is such that the duty can be varied utilizing the temperature characteristics, and it is thus possible to reduce the temperature dependency of the collector current inclination dlc/dt. 
     Fourth Embodiment 
     The basic configuration of a semiconductor device according to a fourth embodiment of the invention is the same as that of the second embodiment shown in  FIG. 6 . The circuit of the fourth embodiment of the invention differs from the second embodiment in that the oscillator  18  in the timer circuit  12  of the second embodiment shown in  FIG. 7  is replaced with a voltage control oscillator  36 .  FIG. 13  shows the voltage control oscillator  36 . The voltage control oscillator  36  has a series circuit wherein an inverter NOT 3 , a MOS Tr 22 , and a MOS Tr 23  are connected in series, a series circuit of an inverted NOT 4  connected in parallel to the MOS Tr 23  and a MOS Tr 24 , a series circuit of an inverter NOT 5  connected in parallel to the MOS Tr 24  and a MOS Tr 25 , a series circuit of an inverter NOT 6  connected in parallel to the MOS Tr 25  and a MOS Tr 26 , and an inverter NOT 2  connected in parallel to a series circuit of the inverters NOT 3  to NOT 6 . The MOSs Tr 22  to Tr 26  are such that the main terminals thereof are short-circuited, and the MOSs Tr 22  to Tr 26  are used as MOS capacitors. A control voltage input terminal Ctrl of the voltage control oscillator  36  is a connection point at which all the main terminals of the MOSs Tr 22  to Tr 26  are connected together. The voltage of the capacitor C 1  is input into the control voltage input terminal Ctrl by the control voltage input terminal Ctr 1  being connected to the connection point of the second series circuit. While an output terminal OSC of the voltage control oscillator  36  may be the output terminal of any one of the inverters NOT 2  to NOT 6 , the output of the inverter NOT 6  is shown as the output terminal OSC in  FIG. 13 . The inverters NOT 2  to NOT 6  are driven by the voltage between the G terminal and E terminal. 
     An outline description will be given of an operation of the voltage control oscillator  36  shown in  FIG. 13 . The inverters NOT 2  to NOT 6  of the voltage control oscillator  36  output a signal to the next stage while inverting the signal. The inverters NOT 2  to NOT 6  output the inverse signal at a predetermined frequency in accordance with a time constant of the MOSs Tr 22  to Tr 26  used as MOS capacitors. Herein, assuming the inverter NOT 2  to be the first stage, and that an H level signal s input, an inverted L level signal is output. Therefore, an L level signal is output from the inverter NOT 6 , and the L level signal is input into the inverter NOT 2 . That is, the outputs of the inverters NOT 2  to NOT 6  oscillate. As the oscillation frequency of the voltage control oscillator  36  is proportional to the voltage input into the control voltage input terminal Ctr 1 , the higher the input voltage, the higher the oscillation frequency. Consequently, by replacing the oscillator  18  of  FIG. 7  with the voltage control oscillator  36  of  FIG. 13 , it is possible to vary the pulse cycle and pulse width of the pulse generator circuit  11 . 
       FIG. 14  shows time charts of the voltage control oscillator  36 , the output signals of the TFFs  20  to  22 , and the pulse signal PULSE 1 . As an outline operation is the same as that of the second embodiment, a description thereof will be omitted, but a difference is that every time the pulse signal PULSE 1  is output at an H level, the frequency of the voltage control oscillator  36  decreases. The decrease in frequency is because, when the pulse signal PULSE 1  is output at an H level, the MOS Tr 5  is turned on, the capacitor C 1  is discharged, and the voltage input into the control voltage input terminal Ctr 1  decreases. in this way, when the voltage of the capacitor C 1  is high, it is possible to shorten the cycle of the output pulse of the pulse signal PULSE 1 , and to reduce the pulse width. 
     Detailed discharge aspects of the pulse signal PULSE 1 , capacitor C 1 , and capacitor C 2  are shown for the second embodiment in  FIG. 15 , and for the fourth embodiment in  FIG. 16 . As shown in these drawings, the duration of the sudden voltage drop when the voltage across the capacitor C 1  is high can be reduced, and the voltage range narrowed, further in the fourth embodiment than in the second embodiment. That is, as it is possible to obtain a still gentler change in the current of the IGBT Tr 2 , it is possible to more reliably prevent erroneous ignition. 
     Examples of specific embodiments are illustrated in the accompanying drawings. While the invention is described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to the described embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In the above description, specific details are set forth in order to provide a thorough understanding of embodiments of the invention. Embodiments of the invention may be practiced without some or all of these specific details. Further, portions of different embodiments and/or drawings can be combined, as would be understood by one of skill in the art. 
     This application is based on, and claims priority to, Japanese Patent Application No. 2012-095767, filed on Apr. 19, 2012, and Japanese Patent Application No. 2012-209948, filed on Sep. 24, 2012. The disclosures of the priority applications, in their entirety, including the drawings, claims, and the specifications thereof, are incorporated herein by reference.