Patent Publication Number: US-2021184564-A1

Title: Drive device and power module

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates to a drive device driving a switching element, and particularly to a drive device having an overcurrent protection function. 
     Description of the Background Art 
     Widely used is a power module supplying current to an inductor load such as a motor using an inverter circuit made up of a series circuit of a switching element on an upper side (P side) and a switching element on a lower side (N side). Known as a drive device driving a switching element is a drive device including an overcurrent detection circuit detecting that overcurrent flows in a switching element and a drive circuit having a function of protecting the switching element from the overcurrent when the overcurrent is detected (an overcurrent protection function). 
     Known as a method of detecting current flowing in a switching element performed by an overcurrent detection circuit is, for example, a method of detecting voltage occurring in a shunt resistance connected between a lower side switching element and a ground terminal (a terminal set in ground potential (GND)) (for example, Japanese Patent Application Laid-Open No. 2017-229119) and a method of adopting a switching element having a current sense terminal in which current, which is substantially proportional to a main current, flows to detect voltage occurring in a sense resistance connected between the current sense terminal and a ground terminal (for example, Japanese Patent Application Laid-Open No. 2019-22348). Used in any method is a comparator comparing voltage occurring in the shunt resistance or the sense resistance and a preset comparison reference voltage. 
     In a general power module, all of reference potential of the comparison reference voltage being input to the comparator of the overcurrent detection circuit, reference potential of the drive circuit driving the switching element, and reference potential of the shunt resistance or the sense resistance are set to have the same value. That is to say, all of the reference potential of the comparison reference voltage, the reference potential of the drive circuit, and the reference potential of the shunt resistance or the sense resistance for the lower side switching element are ground potential, and all of the reference potential of the comparison reference voltage, the reference potential of the drive circuit, and the reference potential of the shunt resistance or the sense resistance for the upper side switching element are potential of a source (emitter) terminal of the upper side switching element (for example, Japanese Patent Application Laid-Open No. 2019-110431). 
     In a configuration that the overcurrent detection circuit detects the voltage of the shunt resistance, when a resistance value of the shunt resistance is increased, the source potential of the switching element easily overshoots and exceeds a gate voltage, and a breaking or erroneous operation of the switching element easily occurs. When the resistance value of the shunt resistance is reduced, the occurrence of this problem can be suppressed, however, if the resistance value of the shunt resistance gets small, voltage occurring in the shunt resistance decreases, thus there arises a problem that a current detection accuracy decreases. 
     SUMMARY 
     An object of the present disclosure is to provide a drive device capable of suppressing an overshoot of source potential of a switching element even when a resistance value of a shunt resistance for detecting current of the switching element is large. 
     A drive device according to the present disclosure includes: an overcurrent detection circuit detecting overcurrent flowing in a switching element based on voltage occurring in a shunt resistance connected to a source of the switching element; and at least one drive circuit applying potential of a connection node of the source of the switching element and the shunt resistance as reference potential and generating a drive signal being input to a gate of the switching element. 
     According to the present disclosure, the reference potential of the drive circuit is the potential of the connection node of the switching element and the shunt resistance, thus the gate potential of the switching element changes in accordance with a fluctuation of the source potential. Thus, even when the source potential of the switching element fluctuates, a change of a gate-source voltage of the switching element is suppressed to a low level. Suppressed accordingly is that the source potential of the switching element overshoots and exceeds the gate voltage even when the resistance value of the shunt resistance is increased. 
     These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing illustrating a configuration of a drive device according to an embodiment 1. 
         FIG. 2  is a drawing for describing an effect obtained by the drive device according to the embodiment 1. 
         FIG. 3  is a drawing for describing an effect obtained by the drive device according to the embodiment 1. 
         FIG. 4  is a drawing illustrating a modification example of the drive device according to the embodiment 1. 
         FIG. 5  is a drawing illustrating a modification example of the drive device according to the embodiment 1. 
         FIG. 6  is a drawing illustrating a configuration of a power module according to an embodiment 2. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
       FIG. 1  is a drawing illustrating a configuration of a drive device  100  according to an embodiment 1.  FIG. 1  illustrates an example that the drive device  100  is a low voltage integrated circuit (LVIC) driving a lower side switching element  2  of an inverter circuit made up of a series circuit of an upper side switching element  1  and the lower side switching element  2 . The inverter circuit supplies current to an inductor load L such as a motor, for example. A shunt resistance  3  for detecting the current is connected between a source of the lower side switching element  2  and a ground terminal. The upper side switching element  1  and the lower side switching element  2  may be a bipolar transistor (BPT) or a metal oxide semiconductor field effect transistor (MOSFET). 
     The drive device  100  includes a drive circuit  10  and an overcurrent detection circuit  20 . The drive circuit  10  generates a drive signal corresponding to an input pulse which is a control signal of the lower side switching element  2 , and inputs the control signal to a gate of the lower side switching element  2 . The overcurrent detection circuit  20  detects overcurrent flowing in the lower side switching element  2  based on voltage occurring in the shunt resistance  3 . 
     The drive circuit  10  includes an NOR gate  11  and a gate logic circuit  12 . The input pulse is input to one input terminal of the NOR gate  11 , and an output signal of the overcurrent detection circuit  20  is input to the other input terminal thereof. The gate logic circuit  12  generates a drive signal corresponding to an output signal of the NOR gate  11 , and inputs the drive signal to the gate of the lower side switching element  2 . Herein, potential of a connection node of the lower side switching element  2  and the shunt resistance  3  (referred to as “the midpoint potential of the lower side switching element  2  and the shunt resistance  3 ” hereinafter) is supplied to the drive circuit  10  as reference potential. Thus, the reference potential of the drive signal being input from the drive circuit  10  to the gate of the lower side switching element  2  is the midpoint potential of the lower side switching element  2  and the shunt resistance  3 . 
     The overcurrent detection circuit  20  includes a comparator  21 , a power source circuit  22  (regulator), and resistance elements  23  to  26 . The resistance elements  23  and  24  are connected in series between the ground terminal and an output terminal the power source circuit  22 , and a connection node between the resistance elements  23  and  24  is connected to an inverting input terminal (− input terminal) of the comparator  21 . The resistance elements  25  and  26  are connected in series between the connection node of the lower side switching element  2  and the shunt resistance  3  and the output terminal the power source circuit  22 , and a connection node between the resistance elements  25  and  26  is connected to a non-inverting input terminal (+ input terminal) of the comparator  21 . 
     That is to say, input to the inverting input terminal of the comparator  21  as a comparison reference voltage is a voltage V 1  obtained by dividing the voltage between the ground potential and the output potential of the power source circuit  22  by the resistance elements  23  and  24 . Input to the non-inverting input terminal of the comparator  21  as voltage for monitoring current flowing in the lower side switching element  2  is a voltage V 2  obtained by dividing the voltage between the midpoint potential of the lower side switching element  2  and the shunt resistance  3  and the output potential of the power source circuit  22  by the resistance elements  25  and  26 . The voltage V 1  is referred to as “the comparison reference voltage” and the voltage V 2  is referred to as “the monitor voltage” hereinafter. 
     In this manner, the resistance elements  23  and  24  constitute a first voltage-dividing circuit for generating the comparison reference voltage V 1 , and the resistance elements  25  and  26  constitute a second voltage-dividing circuit for generating the monitor voltage V 2 . 
     The comparator  21  compares the comparison reference voltage V 1  and the monitor voltage V 2 , thereby determining whether the overcurrent flows in the lower side switching element  2 . That is to say, the comparator  21  determines that the overcurrent flows in the lower side switching element  2  when the monitor voltage V 2  exceeds the comparison reference voltage V 1 , and activates an output signal. The output signal of the comparator  21  (the output signal of the overcurrent detection circuit  20 ) is referred to as “the overcurrent detection signal” hereinafter. The overcurrent detection signal being output from the overcurrent detection circuit  20  is input to the NOR gate  11  of the drive circuit  10  via an OR gate  31  and a delay circuit  32 . One input terminal of the OR gate  31  (an input terminal which does not receive the overcurrent detection signal) is connected to a power-on reset inverting control terminal PR to which a power-on reset inverting control signal is input. Although not shown in the drawings, for example, an error signal such as an overheat protection signal and a low voltage protection signal or a plurality of such error signals may be input to the input terminal of the OR gate  31  which does not receive the overcurrent detection signal instead of the power-on reset inverting control signal. 
     When the overcurrent detection circuit  20  activates the overcurrent detection signal, in the drive circuit  10 , the NOR gate  11  blocks the input pulse, and a drive signal for turning off the lower side switching element  2  is output from the gate logic circuit  12 . Accordingly, the lower side switching element  2  is protected from the overcurrent. 
     As described above, in the conventional power module, all of the reference potential of the comparison reference voltage being input to the comparator of the overcurrent detection circuit, the reference potential of the drive circuit driving the switching element, and the reference potential of the shunt resistance are set to have the same value. In contrast, in the drive device  100  according to the embodiment 1, the reference potential of the comparison reference voltage V 1  being input to the comparator  21  of the overcurrent detection circuit  20  and the reference potential of the shunt resistance  3  are the ground potential, and the reference potential of the drive circuit  10  driving the lower side switching element  2  is the midpoint potential of the lower side switching element  2  and the shunt resistance  3 . 
     The reference potential of the drive circuit  10  is the midpoint potential of the lower side switching element  2  and the shunt resistance  3 , thus as illustrated in  FIG. 2 , the gate potential of the lower side switching element  2  (the potential of the drive signal being output from the drive circuit  10 ) changes in accordance with a fluctuation of a source potential of the lower side switching element  2 . Thus, even when the source potential of the lower side switching element  2  fluctuates, a change of a gate-source voltage of the lower side switching element  2  is suppressed to a low level. Suppressed accordingly is that the source potential of the lower side switching element  2  overshoots and exceeds the gate voltage, thus the resistance value of the shunt resistance  3  can be increased. 
     In the conventional power module, the resistance value of the shunt resistance needs to be set so that voltage appearing in the shunt resistance at the time of occurrence of overcurrent is approximately 0.5V in accordance with a limitation of an operating point or accuracy of a comparator. In contrast, in the drive device  100  of the present embodiment, the comparison reference voltage V 1  is generated by shifting a level of the reference potential (ground potential) of the shunt resistance  3  by the power source circuit  22  and the resistance elements  23  and  24 , and the monitor voltage V 2  is generated by shifting a level of the midpoint potential of the lower side switching element  2  and the shunt resistance  3  by the power source circuit  22  and the resistance elements  25  and  26 . The levels of the comparison reference voltage V 1  and the monitor voltage V 2  can be set by the resistance values (division ratios) of the resistance elements  23  to  26 , thus also obtained is an effect that the resistance value of the shunt resistance  3  can be set to an optional value. The level shifting for generating the comparison reference voltage V 1  and the monitor voltage V 2  may be performed by the other means such as a source follower, for example. 
     The levels of the comparison reference voltage V 1  and the monitor voltage V 2  may be adjustable. For example, each of a series circuit of the resistance elements  23  and  24  (the first voltage-dividing circuit) and a series circuit of the resistance elements  25  and  26  (the second voltage-dividing circuit) may be replaced with a ladder resistance made up of three or more resistance elements so that the node from which the comparison reference voltage V 1  or the monitor voltage V 2  is taken out can be changed. A trimming mechanism for adjusting the output potential may be provided inside the power source circuit  22 . When the levels of the comparison reference voltage V 1  and the monitor voltage V 2  can be adjusted, an input range of the comparator  21  needs not be expanded to a low voltage side, thus the operating point of the comparator  21  can be easily designed, for example. 
     The shunt resistance has a parasitic inductor with a value proportional to an area of the shunt resistance, and in the conventional power module, the shunt resistance is included in a loop of a gate charge current of the lower side switching element, thus an LCR resonance occurs by a gate charge current or an inverse electromotive force of the lower side switching element, and causes an erroneous operation of the overcurrent detection circuit in some cases. In the drive device  100  of the present embodiment, the shunt resistance  3  is separated from the loop of the gate charge current of the lower side switching element  2 , and the loop does not include the parasitic inductor of the shunt resistance  3  (L 31  and L 32  illustrated in  FIG. 3 ), thus also expectable is an effect that the occurrence of LCR resonance can be prevented. 
     When there is a parasitic inductor (L 21 , L 22 , and L 23  illustrated in  FIG. 3 ) in each terminal of the lower side switching element  2  and the resonance occurs due to the large influence of the parasitic inductor (L 21 ) of the source of the lower side switching element  2 , as illustrated in  FIG. 4 , a capacitive element  4  may be connected in parallel to the shunt resistance  3  to move a resonance point, thereby reducing gain in a noise band. Furthermore, as illustrated in  FIG. 5 , a filter circuit  5  for removing a noise may be inserted into a path for supplying the midpoint potential of the lower side switching element  2  and the shunt resistance  3  to the drive circuit  10 . The filter circuit  5  removes the noise other than the resonance. 
     The problem of the resonance tends to occur when di/dt is large, thus it is efficient to apply the capacitive element  4  and the filter circuit  5  when the upper side switching element  1  and the lower side switching element  2  are the switching elements for a high-speed operation. The switching element for the high-speed operation is a switching element made up of a wideband gap semiconductor of SiC, for example. A combination of the upper side switching element  1  and the lower side switching element  2  for the high-speed operation and the capacitance element  4  and the filter circuit  5  enables an implementation of a manufacture driven at a frequency which has been conventionally hard to achieve due to the resonance. 
     The upper side switching element  1 , the lower side switching element  2 , the shunt resistance  3 , and the drive circuit  10  illustrated in  FIG. 1  may be housed in one package to constitute a power module. Alternatively, it is also applicable that the upper side switching element  1 , the lower side switching element  2 , and the drive circuit  10  constitute a power module and the shunt resistance  3  is externally mounted. In the case of the example in  FIG. 4 or 5 , the capacitive element  4  connected in parallel to the shunt resistance  3  may be incorporated into a power module or externally mounted therein. 
     Embodiment 2 
       FIG. 6  is a drawing illustrating a configuration of a power module  200  according to an embodiment 2. The power module  200  is a “6 in 1” type power module including an upper side switching element  1   u  and lower side switching element  2   u  constituting a U phase inverter circuit, an upper side switching element  1   v  and lower side switching element  2   v  constituting a V phase inverter circuit, an upper side switching element  1   w  and lower side switching element  2   w  constituting a W phase inverter circuit, and a high-voltage side drive device  110  and low-voltage side drive device  120  driving those elements. The upper side switching elements  1   u ,  1   v , and  1   w  are driven by the high-voltage side drive device  110  which is a high voltage integrated circuit (HVIC), and the lower side switching elements  2   u ,  2   v , and  2   w  are driven by the low-voltage side drive device  120  which is a low voltage integrated circuit (LVIC). Sources of the lower side switching elements  2   u ,  2   v , and  2   w  are connected to each other, and the shunt resistance  3  is connected between the sources of the lower side switching elements  2   u ,  2   v , and  2   w  and the ground terminal. 
     Although not shown in the drawings, the power module  200  may include a built-in reflux diode connected in anti-parallel to each of the upper side switching elements  1   u ,  1   v , and  1   w  and the lower side switching elements  2   u ,  2   v , and  2   w  and a built-in bootstrap diode supplying a power source to the high-voltage side drive device  110 . The reflux diode and the bootstrap diode may be externally mounted on the power module  200 . When each of the upper side switching elements  1   u ,  1   v , and  1   w  and the lower side switching elements  2   u ,  2   v , and  2   w  is a MOSFET, the reflux diode may be omitted by reason that the MOSFET includes a body diode. 
     In the present embodiment, the drive device  100  of the embodiment 1 is applied to the low-voltage side drive device  120 . That is to say, the low-voltage side drive device  120  includes a drive circuit  10   u  driving the lower side switching element  2   u , a drive circuit  10   v  driving the lower side switching element  2   v , a drive circuit  10   w  driving the lower side switching element  2   w , and the overcurrent detection circuit  20  similar to that in the embodiment 1. Each of the drive circuits  10   u ,  10   v , and  10   w  has the same configuration as the drive circuit  10  of the embodiment 1, and the overcurrent detection signal being output from the overcurrent detection circuit  20  is input to the NOR gate  11  of each of the drive circuits  10   u ,  10   v , and  10   w  via the OR gate  31  and the delay circuit  32 . 
     The effect similar to that in the embodiment 1 can be obtained also in the power module  200  according to the embodiment 2. The power module has the 6 in 1 configuration, thus also obtained is an effect that a common impedance of U phase, V phase, and W phase ground potential can be suppressed. 
     Each embodiment can be arbitrarily combined, or each embodiment can be appropriately varied or omitted. 
     While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention.