Abstract:
A temperature detector for outputting a temperature signal comprises: a temperature sensing diode formed on the same chip as a semiconductor switching device and having a specific temperature vs. voltage characteristic, wherein the temperature detector outputs the anode potential of the temperature sensing diode as the temperature signal; a constant current circuit for supplying a current to the anode of the temperature sensing diode; and anode potential holding means for holding the anode potential of the temperature sensing diode as the temperature signal at the start of switching operation of the semiconductor switching device.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a temperature detector for detecting the temperature of a chip on which a semiconductor switching device or devices are formed, and more particularly to a temperature detector that can avoid outputting erroneous temperature signals during the switching operation of the semiconductor switching device. 
       BACKGROUND ART 
       [0002]    Semiconductor switching devices such as IGBTs (Insulated Gate Bipolar Transistors) will be thermally damaged if they are heated to excessive temperature due to high current operation. To prevent this, a temperature detector is used to detect the temperature of the chip. 
         [0003]      FIG. 10  is a diagram showing the configuration of a conventional temperature detector (see, e.g., Japanese Laid-Open Patent Publication No. 2000-307403). Referring to the figure, a temperature sensing diode  13  is formed on the same chip  12  as a semiconductor switching device  11 . A constant current circuit  14  supplies a constant current to the anode of the temperature sensing diode  13 , and the anode potential of the temperature sensing diode  13  is used as a temperature signal indicating the temperature state of the semiconductor switching device  11 . In this case, the circuit (not shown) that receives the temperature signal is designed to have a high input impedance, as is well known in the art. The forward voltage (Vf) of the temperature sensing diode  13  has a negative temperature coefficient (when the forward current is maintained constant), as shown in  FIG. 11 . 
         [0004]    It should be noted that during the switching operation of the semiconductor switching device  11 , negative noise is superimposed on the anode potential of the temperature sensing diode  13  due to wire inductance, loops, etc., resulting in a reduction in the anode potential. To prevent this, a CR filter  15  is inserted between the anode of the temperature sensing diode  13  and the output terminal to shape the temperature signal. 
         [0005]    However, as the switching frequency increases, the potential of the temperature signal from the temperature sensing diode  13  gradually decreases, as shown in  FIG. 12 . Therefore, a conventional temperature detector may output an erroneous output signal even if the temperature signal from the temperature sensing diode  13  is shaped by the above filter, since the portions of the temperature signal affected by the negative noise may have a lower potential level than a predetermined threshold level. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention has been devised to solve the above problem. It is, therefore, an object of the present invention to provide a temperature detector that can avoid outputting erroneous temperature signals during the switching operation of the semiconductor switching device. 
         [0007]    According to one aspect of the present invention, a temperature detector for outputting a temperature signal comprises: a temperature sensing diode formed on the same chip as a semiconductor switching device and having a specific temperature vs. voltage characteristic, wherein the temperature detector outputs the anode potential of the temperature sensing diode as the temperature signal; a constant current circuit for supplying a current to the anode of the temperature sensing diode; and anode potential holding means for holding the anode potential of the temperature sensing diode as the temperature signal at the start of switching operation of the semiconductor switching device. 
         [0008]    Thus, the present invention provides a temperature detector that can avoid outputting erroneous temperature signals during the switching operation of the semiconductor switching device. 
         [0009]    Other and further objects, features and advantages of the invention will appear more fully from the following description. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a diagram showing the configuration of a temperature detector according to a first embodiment of the present invention. 
           [0011]      FIG. 2  is a timing chart showing the operation of the temperature detector shown in  FIG. 1 . 
           [0012]      FIG. 3  is a diagram showing the configuration of a temperature detector according to a second embodiment of the present invention. 
           [0013]      FIG. 4  is a diagram showing the configuration of a temperature detector according to a third embodiment of the present invention. 
           [0014]      FIG. 5  is a diagram showing the configuration of a temperature detector according to a fourth embodiment of the present invention. 
           [0015]      FIG. 6  is a diagram showing the configuration of a temperature detector according to a fifth embodiment of the present invention. 
           [0016]      FIG. 7  is a diagram showing the configuration of second switching means. 
           [0017]      FIG. 8  is a timing chart showing the operation of the temperature detector shown in  FIG. 6 . 
           [0018]      FIG. 9  is a diagram showing the configuration of a constant current circuit according to a sixth embodiment of the present invention. 
           [0019]      FIG. 10  is a diagram showing the configuration of a conventional temperature detector. 
           [0020]      FIG. 11  is a diagram showing the temperature vs. voltage characteristics of a temperature sensing diode. 
           [0021]      FIG. 12  is a timing chart showing the operation of the temperature detector shown in  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       [0022]      FIG. 1  is a diagram showing the configuration of a temperature detector according to a first embodiment of the present invention, and  FIG. 2  is a timing chart showing the operation of the temperature detector. 
         [0023]    As shown in  FIG. 1 , a temperature sensing diode  13  is formed on the same chip  12  as a semiconductor switching device  11  (an IGBT, etc.). The forward voltage of the temperature sensing diode  13  has a negative temperature coefficient when the forward current is maintained at a constant level. The cathode of the temperature sensing diode  13  is grounded. A constant current circuit  14  supplies a constant current of approximately 2 mA to the anode of the temperature sensing diode  13 , and the anode potential of the temperature sensing diode  13  is output as a temperature signal. It should be noted that the voltage drop between both terminals of an individual temperature sensing diode is approximately 0.6 V (at 25° C.), and therefore a plurality of series-connected temperature sensing diodes are usually formed on the chip  12  to provide a combined voltage of approximately 2 V (and used as the temperature sensing diode  13 ). 
         [0024]    Further, an anode potential holding means  16  is inserted between the anode of the temperature sensing diode  13  and the output terminal. The anode potential holding means  16  holds the anode potential of the temperature sensing diode  13  as a temperature signal at the start of (each turn-on operation in) the switching operation of the semiconductor switching device  11 . 
         [0025]    Specifically, the anode potential holding means  16  includes a capacitor  17 , a one-shot pulse generating circuit  18 , and a first switching means  19 . One end of the capacitor  17  is connected between the anode of the temperature sensing diode  13  and the output terminal, while the other end is grounded. The one-shot pulse generating circuit  18  generates a control signal Sc in response to the gate drive signal (input signal) Sg to the semiconductor switching device  11 . The control signal Sc is set at a low level for a predetermined period of time each time the gate drive signal Sg rises. Except for these periods, the control signal Sc is set at a high level. The first switching means  19  disconnects the anode of the temperature sensing diode  13  from the one end of the capacitor  17  while the control signal Sc from the one-shot pulse generating circuit  18  is at a low level, that is, for a predetermined period of time from the start of (each turn-on operation in) the switching operation of the semiconductor switching device  11 . It should be noted that the switching means may be implemented by a MOS transistor, etc., and the one-shot pulse generating circuit may be made up of a timer or a filter. 
         [0026]    Thus, the anode potential holding means  16  prevents the anode potential of the temperature sensing diode from being output when its level is lowered due to negative noise during the switching operation of the semiconductor switching device, which allows the temperature detector to avoid outputting erroneous signals. 
       Second Embodiment 
       [0027]      FIG. 3  is a diagram showing the configuration of a temperature detector according to a second embodiment of the present invention. The temperature detector of this embodiment is different from that of the first embodiment in that the anode potential holding means  16  additionally includes a first negative feedback amplifier  21 , a second negative feedback amplifier  22 , diodes  23  and  24 , and a resistance  25 . All other components are similar to those described in connection with the first embodiment. 
         [0028]    The first negative feedback amplifier  21  receives the anode potential of the temperature sensing diode  13  on its noninverting input terminal. The second negative feedback amplifier  22 , on the other hand, receives the output voltage of the first negative feedback amplifier  21  on its noninverting input terminal and outputs a temperature signal. The output of the second negative feedback amplifier  22  is fed back to its own inverting input terminal and to the inverting input terminal of the first negative feedback amplifier  21  through the resistance  25 . Further, one end of the diode  23  is connected between the resistance  25  and the inverting input terminal of the first negative feedback amplifier  21 , while the other end is connected to the output side of the first negative feedback amplifier  21 . The diode  24  and the diode  23  are connected in parallel in reverse polarity. 
         [0029]    Having the above configuration, the anode potential holding means  16  prevents the anode potential of the temperature sensing diode from being output when its level is lowered due to negative noise during the switching operation of the semiconductor switching device, which allows the temperature detector to avoid outputting erroneous signals, as in the case of the first embodiment. Further, the circuit connected to the anode of the temperature sensing diode  13  has high impedance and hence does not affect the anode potential very much. Further, since the anode potential holding means  19  has a two stage negative feedback configuration, the detection error of the temperature detector is very small and the temperature detection response speed can be increased. Still further, the output impedance of the anode potential holding means  16  can be adjusted, eliminating the need to increase the input impedance of the circuit side (not shown) that receives the temperature signal. This means that the circuit connected to the output of the anode potential holding means  16  can have any arbitrary configuration, which leads to wider application of the temperature detector. Since the gain of the second negative feedback amplifier is stable, the detection signal is highly stable with parameter variations, such as power voltage and temperature variations, and with time. Further, since the anode potential holding means  16  (or the temperature detector) outputs the temperature signal through an amplifier (i.e., the second negative feedback amplifier  22 ), its output impedance can be adjusted to a desired value. 
       Third Embodiment 
       [0030]      FIG. 4  is a diagram showing the configuration of a temperature detector according to a third embodiment of the present invention. The temperature detector of this embodiment is different from that of the first embodiment in that the anode potential holding means  16  additionally includes a first negative feedback amplifier  21 , a second negative feedback amplifier  22 , and resistances  26  and  27 . All other components are similar to those described in connection with the first embodiment. 
         [0031]    The first negative feedback amplifier  21  receives the anode potential of the temperature sensing diode  13  on its noninverting input terminal. The second negative feedback amplifier  22 , on the other hand, receives the output voltage of the first negative feedback amplifier  21  on its noninverting input terminal and outputs a temperature signal. The output of the second negative feedback amplifier  22  is grounded via the resistances  26  and  27 , and the connection point between the resistances  26  and  27  is connected to the inverting input terminal of the amplifier  22 . 
         [0032]    The gain of the second negative feedback amplifier  22  can be varied by varying the values of the resistances  26  and  27 , which produces the same effect as the second embodiment. Furthermore, the temperature signal can be amplified to a desired voltage level, resulting in reduced temperature signal errors. 
       Fourth Embodiment 
       [0033]      FIG. 5  is a diagram showing the configuration of a temperature detector according to a fourth embodiment of the present invention. The temperature detector of this embodiment is different from that of the first embodiment in that the anode potential holding means  16  additionally includes a first negative feedback amplifier  21  and a second negative feedback amplifier  22 . All other components are similar to those described in connection with the first embodiment. 
         [0034]    The first negative feedback amplifier  21  receives the anode potential of the temperature sensing diode  13  on its noninverting input terminal. The second negative feedback amplifier  22 , on the other hand, receives the output voltage of the first negative feedback amplifier  21  on its noninverting input terminal and outputs a temperature signal. Further, the output signal of the second negative feedback amplifier  22  is fed back to its own inverting input terminal and to the inverting input terminal of the first negative feedback amplifier  21 . 
         [0035]    The present embodiment provides a lower cost configuration than the second embodiment, but produces the same effect as the second embodiment. 
       Fifth Embodiment 
       [0036]      FIG. 6  is a diagram showing the configuration of a temperature detector according to a fifth embodiment of the present invention. The temperature detector of this embodiment is different from that of the first embodiment in that it additionally includes a second switching means  28 . All other components are similar to those described in connection with the first embodiment. 
         [0037]      FIG. 7  is a diagram showing the configuration of the second switching means  28 . Referring to the figure, the second switching means  28  includes NMOS transistors  31  to  33 . The drain of each transistor is connected to a power supply (voltage), and a control signal Sc is input from the one-shot pulse generating circuit  18  to the gate of the transistor  31 . The sources of the transistors  31  and  32  and the gates of the transistors  31  and  33  are connected to the constant current circuit  14 . Further, a bias current Ia is supplied from the source of the transistor  33  to the anode of the temperature sensing diode  13 . 
         [0038]      FIG. 8  is a timing chart showing the operation of the temperature detector shown in  FIG. 6 . As shown in the figure, the second switching means  28  stops the supply of the bias current from the constant current circuit  14  to the anode of the temperature sensing diode  13  for a predetermined period of time from the start of (each turn-on operation in) the switching operation of the semiconductor switching device  11 . That is, the second switching means  28  supplies the bias current during each anode potential detection period and stops its supply during each anode potential holding period. This reduces power consumption, as well as achieving the same effect as the first embodiment. It should be noted that the present embodiment may be combined with the second to fourth embodiments. 
       Sixth Embodiment 
       [0039]      FIG. 9  is a diagram showing the configuration of a temperature detector according to a sixth embodiment of the present invention. The temperature detector of this embodiment is different from that of the fifth embodiment in that the anode potential holding means  16  additionally includes a periodic signal generator  34  and an AND circuit  35 . All other components are similar to those described in connection with the fifth embodiment. 
         [0040]    The periodic signal generator  34  generates a periodic signal starting from the start of the switching operation of the semiconductor switching device  11 . The AND circuit  35  receives this periodic signal and the output signal of the one-shot pulse generating circuit  18  and performs a logical AND operation on them to output a control signal Sc to the first switching means  19  and the second switching means  28 . 
         [0041]    The first and second switching means  19 ,  28  operate in synchronization with the periodic signal (or the control signal Sc). Thus, the present embodiment allows the control signal to be finely divided (or allows the period of the control signal to be finely adjusted), resulting in a further reduction in the power consumption, as compared to the fifth embodiment. 
         [0042]    According to a variation of the present embodiment, the AND circuit  35  receives a control signal from an external device, instead of the periodic signal from the periodic signal generator  34  shown in  FIG. 9 . Such an arrangement allows the external device (that is, the circuit or system side that receives the temperature signal) to control the operational state of the temperature detector. This means that the circuit or system side can control the temperature detector such that the detector operates only when the circuit or system side needs to receive the temperature signal, which further reduces power consumption. 
         [0043]    Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. 
         [0044]    The entire disclosure of a Japanese Patent Application No. 2006-250765, filed on Sep. 15, 2006 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety.