Patent Publication Number: US-2022230794-A1

Title: Current control device

Description:
TECHNICAL FIELD 
     The present invention relates to a current control device, and more particularly to a current control device that controls a current flowing through a solenoid that is an inductive load. 
     BACKGROUND ART 
     A current control device for a solenoid, used in a vehicle automatic transmission or the like, measures a current value flowing through the solenoid, and controls the current by performing feedback to a pulse width modulation signal (hereinafter, referred to as PWM signal) for adjusting ON and OFF timings of a switch element controlling energization to the solenoid such that the measured current value matches a desired current value. 
       FIG. 9  illustrates a conventional example of the current control device. A conventional current control device  500  illustrated in  FIG. 9  is configured such that one end of a solenoid  110  is connected to a connection point between a high-side switch element  40  and a low-side switch element  50  connected in series to a battery power source (VB)  150 , and the other end of the solenoid  110  is connected to a ground power source (GND)  120 , thereby exclusively performing ON and OFF control of the high-side switch element  40  and the low-side switch element  50  according to a PWM signal (PMW_IN 1 )  11  from a microcontroller (hereinafter, sometimes referred to as microcomputer)  200  and supplying a current to the solenoid  110 . When the PWM signal  11  is at a high level, the high-side switch element  40  is turned on, and the low-side switch element  50  is turned off, so that the battery power source  150  supplies the current to the solenoid  110  via the high-side switch element  40 . On the other hand, when the PWM signal  11  is at a low level, the low-side switch element  50  is turned on, and the high-side switch element  40  is turned off, so that the current supply from the battery power source  150  is stopped. Here, when the current supplied from the battery power source  150  is cut off, a counter electromotive force is generated in the solenoid  110 . Thus, the current is supplied from a ground power source (GND)  160  via the low-side switch element  50 , and the energy accumulated in the solenoid  110  is released. The current supplied to the solenoid  110  is supplied via the high-side switch element  40  or the low-side switch element  50  according to the polarity of the PWM signal  11 , and the supplied current is controlled by adjusting a high-level time of the PWM signal  11 ÷a PWM signal cycle (hereinafter, referred to as a duty ratio). 
     Such a current control device  500  typically includes: a high-side (HS) current measurement circuit  60  that detects and measures a current value flowing through the solenoid  110  via the high-side switch element  40 ; a low-side (LS) current measurement circuit  70  that detects and measures a current value flowing through the solenoid  110  via the low-side switch element  50 ; a current calculation circuit  80  that obtains an average current value for a certain period necessary for feedback control based on current detection results of the HS current measurement circuit  60  and the LS current measurement circuit  70  and transfers the average current value to the microcomputer  200 ; and a switch control circuit  30  that receives the PWM signal (PMW_IN 1 )  11  from the microcomputer  200 , generates a high-side switch element control PWM signal  31  for the high-side switch element  40  (hereinafter, simply referred to as PWM signal  31 ) and a low-side switch element control PWM signal  32  for the low-side switch element  50  (hereinafter, simply referred to as PWM signal  32 ), and executes switch control (also referred to as gate control) to turn on and off the high-side switch element  40  and the low-side switch element  50 . The high-side switch element  40 , the low-side switch element  50 , and the above-described various circuits constitute a load drive circuit (synchronous rectification circuit)  10  that supplies a current to the solenoid  110  which is an inductive load. 
     In addition, it is also known that a load drive circuit corresponding to each solenoid is provided in the current control device  500  in a case where a plurality of solenoids are controlled by the current control device  500  (see, for example, PTL 1 below). 
     CITATION LIST 
     Patent Literature 
     PTL 1: WO 2017/057682 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     In a case where one end of the solenoid connected to the current control device is grounded to the ground power source, a current is supplied from the current control device to the solenoid. When the duty ratio of the PWM signal from the microcontroller is “0”, the current value is the minimum value “0”. Since the amount of the current supplied to the solenoid increases as the duty ratio is increased, it is difficult for such a current control device to control a current in the reverse direction from the normal direction from the solenoid to the current control device. However, when an abnormality such as disconnection of a ground line of an electronic control device or the solenoid occurs, an unintended reverse current occurs in some cases. 
       FIG. 10  illustrates another conventional example of the current control device. A conventional current control device  600  illustrated in  FIG. 10  controls a plurality of solenoids in which one end of each of the solenoids is connected to a common ground point (ground power source). In a case where one solenoid  110   a  is controlled by a PWM signal (PMW_IN 1 )  11   a  having a low duty ratio (sent from a microcomputer  200  to a load drive circuit  10   a ) and the other solenoid  110   b  is controlled by a PWM signal (PMW_IN 2 )  11   b  having a relatively high duty ratio (sent from the microcomputer  200  to a load drive circuit  10   b ), a node  170  connected to a ground power source  160  has a high impedance and is likely to fluctuate, for example, if the current control device  600  and the ground power source  160  are disconnected, so that a relatively large current Is from the current control device  600  to the solenoid  110   b  acts in a direction of decreasing a potential of the node  170 . Then, a current flowing through the solenoid  110   b  flows from the solenoid  110   a  to the node  170  of the current control device  600  via a low-side switch element  50 , which is kept substantially in an ON state by the PWM signal  11   a  having a low duty ratio, thereby generating a reverse current Irev. 
     Some solenoids open and close valves even by a reverse current. For example, in a solenoid that controls disconnection of a lock-up clutch, there is a possibility that an unintended lock-up is fastened by the generated reverse current to generate a shift shock. 
     Regarding such a problem, in the related art described in PTL 1 described above, it is determined that a disconnection abnormality of solenoids to a common ground point has occurred when a detected value of a current flowing through the solenoids is lower than an instruction value of a current or a reverse current is detected, and control is performed to stop all the solenoids. However, such a measure is taken assuming that one end of each of the solenoids has the disconnection abnormality for the common ground point, and there is a high possibility that a shift shock occurs since all the solenoids are turned off. 
     The present invention has been made in view of the above problems, and an object thereof is to provide a current control device capable of continuing feedback control for a solenoid in normal feedback control while preventing the occurrence of an unintended valve operation due to flow of a reverse current. 
     Solution to Problem 
     In order to solve the above problems, a current control device according to the present invention includes: a high-side switch element that electrically connects a solenoid, which has one end grounded to a ground power source, to a battery power source; a low-side switch element that electrically connects the solenoid to the ground power source; a switch control circuit that controls a supply current with respect to the solenoid by turning on one of the high-side switch element and the low-side switch element and turning off the other; and a time measurement circuit that measures an ON duration of the low-side switch element. 
     Advantageous Effects of Invention 
     According to the present invention, provided are: the high-side switch element that electrically connects the solenoid, which has one end grounded to the ground power source, to the battery power source; the low-side switch element that electrically connects the solenoid to the ground power source; the switch control circuit that controls the supply current with respect to the solenoid by turning on one of the high-side switch element and the low-side switch element and turning off the other; and the time measurement circuit that measures the ON duration of the low-side switch element. When the ON duration of the low-side switch element measured by the time measurement circuit reaches a predetermined time, the switch control circuit temporarily turns off the low-side switch element while keeping the high-side switch element off. 
     That is, in a case where the current to be supplied to the solenoid is controlled by a PWM signal having a low duty ratio, in particular, by a PWM signal having a duty ratio corresponding to an instruction current value of the current “0”, if a certain time elapses in such a state, the low-side switch element is temporarily turned off, and a current path in the reverse direction is cut off in advance in order to prevent a reverse current. If a PWM signal indicating that the instruction current value is not “0” but is a certain value or more is received, the fixation of the low-side switch element in the OFF state is released to return to a normal synchronous rectification operation in which either the high-side switch element or the low-side switch element is turned on. 
     As a result, the path of the reverse current of the solenoid is cut off by a simpler method, and feedback control can be continued for the solenoid capable of performing normal feedback control while preventing the occurrence of an unintended valve operation due to the flow of the reverse current. As a result, in the solenoid that controls disconnection of a lock-up clutch, it is possible to suppress the occurrence of a shift shock while preventing fastening of an unintended lock-up when a ground line is disconnected, for example. 
     Other objects, configurations, and effects which have not been described above become apparent from embodiments to be described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a configuration diagram illustrating a first embodiment of the present invention. 
         FIG. 2  is a configuration diagram illustrating a modification of the first embodiment of the present invention. 
         FIG. 3  is a view illustrating a first operation waveform example of the first embodiment of the present invention. 
         FIG. 4  is a view illustrating an operation waveform example in a case where a threshold time in  FIG. 3  depends on a detected current value. 
         FIG. 5  is an explanatory view for simply obtaining the threshold time in  FIG. 4 . 
         FIG. 6  is a view illustrating a second operation waveform example of the first embodiment of the present invention. 
         FIG. 7  is a configuration diagram illustrating a second embodiment of the present invention. 
         FIG. 8  is a view illustrating an operation waveform example of the second embodiment of the present invention. 
         FIG. 9  is a configuration diagram of a conventional current control device. 
         FIG. 10  is a configuration diagram illustrating an example of a problem in a conventional current control device. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. Incidentally, a technical scope of the present invention should not be narrowly interpreted based on the description of the drawings since the drawings are simplified. In addition, the same elements are denoted by the same reference signs in the description of the present specification, and redundant descriptions thereof are omitted. 
     First Embodiment 
       FIG. 1  is a configuration diagram of a current control device for a vehicle automatic transmission according to a first embodiment of the present invention. 
     A current control device  100  of the illustrated embodiment includes a microcomputer  200  and load drive circuits  10   a  and  10   b  that supply currents to a plurality of solenoids  110   a  and  110   b . Here, the number of the plurality of solenoids and the number of the load drive circuits are omitted to two (two sets) for the simplification of the drawing, but the number is not limited. In addition, in both of the load drive circuits  10   a  and  10   b , one end of each of the solenoids  110   a  and  110   b  that supplies a current is connected to a connection point between a high-side switch element  40  and a low-side switch element  50  connected in series to a battery power source (VB)  150 , and the other end of each of the solenoids  110   a  and  110   b  is connected (grounded) to a common ground power source (GND)  120 . The microcomputer  200  calculates currents to be supplied to the solenoids  110   a  and  110   b  necessary for a vehicle automatic transmission system, and outputs PWM signals  11   a  and  11   b  for controlling ON and OFF timings of the high-side switch element  40  and the low-side switch element  50  to the load drive circuits  10   a  and  10   b  using values of the currents as instruction current values. 
     Since a configuration and an operation of each of the load drive circuit  10   a  and the load drive circuit  10   b  are basically the same, the configuration and operation of the load drive circuit  10   a  provided for the solenoid  110   a  will be mainly described hereinafter. 
     When the PWM signal  11   a  is at a high level by a switch control circuit  30 , the load drive circuit  10   a  that has received the PWM signal  11   a  generates PWM signals  31  and  32  so as to turn on the high-side switch element  40  and turn off the low-side switch element  50 , and supplies a current from the battery power source  150  to the solenoid  110   a  via the high-side switch element  40 . On the other hand, when the PWM signal  11   a  is at a low level, the PWM signals  31  and  32  are generated so as to turn off the high-side switch element  40  and turn on the low-side switch element  50 , the current supply from the battery power source  150  is cut off, and energy accumulated in the solenoid  110   a  is discharged by supplying a current from a ground power source (GND)  160  to the solenoid  110   a  via the low-side switch element  50 . Since a transition time is required for the high-side switch element  40  and the low-side switch element  50  to be switched from ON to OFF and from OFF to ON, a period (hereinafter, referred to as dead-time period) for controlling both the switch elements to be turned off is added to the PWM signals  31  and  32  at a switching timing between ON and OFF such that both the high-side switch element  40  and the low-side switch element  50  are not turned on. As a result, the current supplied to the solenoid  110   a  can be increased or decreased by changing a duty ratio of the PWM signal  11   a , and the supply current with respect to the solenoid  110   a  is controlled by performing feedback control so as to correct a difference between the instruction current value calculated by the microcomputer  200  and the current value flowing through the solenoid  110   a  for the PWM signal  11   a  of the duty ratio. The current value flowing through the solenoid  110   a  is detected by an HS current measurement circuit  60  and an LS current measurement circuit  70  for each of the high-side switch element  40  and the low-side switch element  50 . A current calculation circuit  80  effectively obtains an average current value for a certain period required for the feedback control based on a result of the current detection, and transfers the average current value to the microcomputer  200 . 
     In addition to the above configuration, in the first embodiment, an HS/LS control time measurement circuit  20  that measures a high-level period and a low-level period of the PWM signal  11   a  is provided in order to measure ON (or OFF) control times (also referred to as ON durations) of the high-side switch element  40  and the low-side switch element  50 . For example, a reverse current is unintentionally generated from the solenoid  110   a  to the current control device  100  due to disconnection of a GND connection line of the current control device  100  or the like in a period in which the low-side switch element  50  is turned on, and in a case where the current value supplied to the solenoid  110   a  is small. In particular, such a risk increases if the instruction current value of the solenoid  110   a  is near “0”. Therefore, the high-level period and the low-level period of the PWM signal  11   a  are measured by the HS/LS control time measurement circuit  20 , and when an ON period of the low-side switch element  50  with the PWM signal  11   a  is sufficiently long and the instruction current value is recognized as “0”, the low-side switch element  50  is temporarily turned off by the switch control circuit  30  to prevent the generation of the reverse current in advance. 
     Here, the HS/LS control time measurement circuit  20  may measure an ON control time (ON duration) of low-side switch element  50  to be used for control or measure an OFF control time (OFF duration) of the high-side switch element  40  to detect the ON control time (ON duration) of the low-side switch element  50  from the OFF control time. 
     Incidentally, the HS/LS control time measurement circuit  20  is installed for the PWM signal  11   a  (that is, in the upstream side of the switch control circuit  30 ) in  FIG. 1 , but may be installed for the PWM signal  31  and the PWM signal  32  (that is, between the switch control circuit  30 , and the high-side switch element  40  and the low-side switch element  50 ) as illustrated in  FIG. 2  in consideration of a control timing as long as the ON (or OFF) control times of the high-side switch element  40  and the low-side switch element  50  can be measured. In the example illustrated in  FIG. 1 , the ON (or OFF) control time can be measured earlier. In the example illustrated in  FIG. 2 , the ON (or OFF) control time can be measured more accurately. 
       FIG. 3  is an operation timing chart of a function of preventing generation of a reverse current in the first embodiment. Incidentally, the description of the dead-time period is omitted for the PWM signals  31  and  32 , which are control signals of the high-side switch element  40  and the low-side switch element  50  for the sake of simplicity.  FIG. 3  first illustrates the simplest example in which the duty ratio of the PWM signal  11   a  becomes zero when the instruction current value is “0”. 
     The PWM signal  11   a  is controlled with a cycle tPWM_CYC, and one of the high-side switch element  40  and the low-side switch element  50  is (exclusively) turned on by the switch control circuit  30  according to the polarity of the PWM signal  11   a  to control the current supplied to the solenoid  110   a . Here, the HS/LS control time measurement circuit  20  measures the low-level period corresponding to the ON time of the low-side switch element  50  every time the PWM signal  11   a  is switched from the high level to the low level (in  FIG. 3 , low-side ON time measurement). If the low-level period of the PWM signal  11   a  becomes longer than a certain threshold time tLS_OFF, the PWM signal  32  is negated, the switch control circuit  30  performs control to turn off both the high-side switch element  40  and the low-side switch element  50  (in other words, performs control to turn off the low-side switch element  50  while keeping the high-side switch element  40  off), thereby preventing the generation of the reverse current in advance. If the threshold time tLS_OFF for which the low-side switch element  50  is temporarily turned off is set to be equal to or longer than the ON/OFF switching cycle tPWM_CYC of the low-side switch element  50  and the high-side switch element  40 , this function can be enabled only when the duty ratio of the PWM signal  11   a  with the instruction current value of “0” becomes “0”. A state where both the high-side switch element  40  and the low-side switch element  50  are temporarily turned off is continued until the PWM signal  11   a  is switched to the high level (that is, until the PWM signal  11   a  as a control command for turning on the high-side switch element  40  is generated and the instruction current value is no longer “0”). Thereafter, the control returns to normal PWM control (that is, a synchronous rectification operation) according to the polarity of the PWM signal  11   a.    
     Here, regarding the threshold time tLS_OFF for the low-level period of the PWM signal  11   a , it is necessary to wait until a current decreases to some extent since it is not preferable to turn off the low-side switch element  50  while a large current is supplied from the low-side switch element  50  to the solenoid  110   a . This is because the low-side switch element  50  is generally formed using a metal-oxide semiconductor field-effect transistor (MOSFET), and unexpected heat generation occurs since a current flows through a parasitic diode of the MOSFET even when the switch element is turned off, and it is difficult to measure a value of the current flowing therebetween depending on the configuration of the current measurement circuit so that an error occurs in a measured current value. The current value supplied to the solenoid  110   a  when the low-side switch element  50  is turned on depends on an ON resistance of the low-side switch element  50 , an impedance of the solenoid  110   a , and the energy accumulated in the solenoid  110   a  while the high-side switch element  40  is turned on. 
     When the ON resistance of the low-side switch element  50  is Ron, the inductance of the solenoid  110   a  is Ls, a resistance value is Rs, and a peak current value when the high-side switch element  50  is turned on is Ipk, a current I, supplied to the solenoid  110   a  after a lapse of time t since switching of the low-side switch element  50  to an ON state, can be approximated by the following Formula (1). 
       [Formula 1] 
         I=Ipk *exp(−( Rs+Ron )* t/Ls )  (1)
 
     In addition, when a current value after a lapse of time t is Igoal, the time t is expressed by the following Formula (2). 
       [Formula 2] 
         t=Ls /( Rs+Ron )*ln( Ipk /Igoal)  (2)
 
     Here, Ls, Rs, and Ron are known. As illustrated in  FIG. 4 , if current values supplied to the solenoid  110   a  are acquired at the timing when the PWM signal  11   a  is switched to the low level by the HS current measurement circuit  60  and the LS current measurement circuit  70  when the low-side switch element  50  is turned on, tLS_OFF for desired Igoal can be obtained with Ipk. It is preferable that Igoal be a value which makes a stress (current value) generated by turning off the low-side switch element  50  fall within an allowable range of a device circuit device (that is, the load drive circuit  10   a  of the current control device  100 ) and has an error that can be ignored in terms of accuracy of the measured current value. In other words, the threshold time tLS_OFF for temporarily turning off the low-side switch element  50  (tLS_OFF obtained for Igoal described above) is preferably set to a time in which the stress (current value) generated by cutting off the current flowing from the low-side switch element  50  to the solenoid  100   a  decreases to a current value within the allowable range of the device circuit device (that is, the load drive circuit  10   a  of the current control device  100 ). In addition, the calculation of ln( ) in the above Formula (2) can be easily realized by a method of obtaining Ipk acquired every PWM cycle by a first-order approximation formula divided into several current ranges as illustrated in  FIG. 5 . In addition, more simply, Ipk may be calculated assuming (fixing) a maximum current value (=battery voltage/(Rs+Ron)) at a duty ratio of 100% of the PWM signal  11   a.    
     Incidentally, the case where the duty ratio of the PWM signal  11   a  having the instruction current value of “0” is “0” is assumed in  FIG. 3  described above. However, in practice, there is a case where an extremely small duty ratio that is not “0” is held (that is, case where the PWM signal  11   a  as the control command for turning on the high-side switch element  40  is generated).  FIG. 6  illustrates an operation timing chart of a function of preventing generation of a reverse current in a case where the duty ratio of the PWM signal  11   a  having the instruction current value of “0” is not “0” (case where the instruction current value is “0” but an extremely small duty ratio that is not “0” is held). Incidentally,  FIG. 6  illustrates a time delay (here, tPWMLH_TH) for securing a determination time for input and output in the switch control circuit  30 , that is, the PWM signals  31  and  32  with respect to the PWM signal  11   a.    
     The PWM signal  11   a  is controlled with the cycle tPWM_CYC, and one of the high-side switch element  40  and the low-side switch element  50  is (exclusively) turned on by the switch control circuit  30  according to the polarity of the PWM signal  11   a  to control the current supplied to the solenoid  110   a , which is similar to the case of  FIG. 3 . Here, the HS/LS control time measurement circuit  20  measures the low-level period corresponding to the ON time of the low-side switch element  50  every time the PWM signal  11   a  is switched from the high level to the low level as described above. However, when the instruction current value is “0” and the duty ratio of the PWM signal  11   a  is not “0” as in the present example, the PWM signal  11   a  changes to the high level every cycle tPWM_CYC. Therefore, the high-level period (that is, an ON duration of the high-side switch element  40 ) of the PWM signal  11   a  (the PWM signal  31  in the case of the example illustrated in  FIG. 2 ) is measured by the HS/LS control time measurement circuit  20 , and the measurement of the low-level period (that is, the ON duration of the low-side switch element  50 ) is continued as it is without being initialized (or canceled) if the measured high-level period is a time shorter than the determination threshold tPWMLH_TH of the high-level period in which it can be determined that the instruction current value is “0”. That is, in this case, the determination threshold tPWMLH_TH of the high-level period (the ON duration of the high-side switch element  40 ) of the PWM signal  11   a  (the PWM signal  31  in the case of the example illustrated in  FIG. 2 ) is set based on the ON period of the high-side switch element  40  when the current value supplied to the solenoid  110   a  is controlled to “0”. Then, if the low-level period is longer than a certain threshold time tLS_OFF, the PWM signal  32  is negated, and the switch control circuit  30  performs control to temporarily turn off both the high-side switch element  40  and the low-side switch element  50  (in other words, performs control to turn off the low-side switch element  50  while keeping the high-side switch element  40  off), thereby preventing the generation of the reverse current in advance. 
     In this case, this function can be enabled only when the instruction current value becomes “0” if the threshold time tLS_OFF is set to be equal to or longer than a value obtained by adding tPWMLH_TH to the cycle tPWM_CYC and the time delay (here, tPWMLH_TH) of the PWM signals  31  and  32  with respect to the PWM signal  11   a . Such a state where both the high-side switch element  40  and the low-side switch element  50  are temporarily turned off is continued until a signal that makes the high-level period of the PWM signal  11   a  equal to or longer than the determination threshold tPWMLH_TH is input (that is, the PWM signal  11   a  as the control command for turning on the high-side switch element  40  is generated for the determination threshold tPWMLH_TH or longer and the instruction current value is no longer “0”). As a result, the generation of the reverse current can be prevented in advance even in the case where the duty ratio of the PWM signal  11   a  is not “0” when the instruction current value is “0”. 
     In addition, the above example is limited to the case where the instruction current value is “0”, but the generation of the reverse current can be prevented in advance even for an instruction current value that is not “0” by adjusting the determination threshold tPWMLH_TH of the high-level period of the PWM signal  11   a  although causing a trade-off with the measurement current accuracy. 
     According to the present invention, provided are: the high-side switch element  40  that electrically connects each of the solenoids  110   a  and  110   b  having one ends grounded to the ground power source  120 , to the battery power source  150 ; the low-side switch element  50  that electrically connects the solenoid to the ground power source  160 ; the switch control circuit  30  that controls the supply current with respect to each of the solenoids  110   a  and  110   b  by turning on one of the high-side switch element  40  and the low-side switch element  50  and turning off the other; and the HS/LS control time measurement circuit (time measurement circuit)  20  that measures the ON duration of the low-side switch element  50 . When the ON duration of the low-side switch element  50  measured by the HS/LS control time measurement circuit (time measurement circuit)  20  reaches a predetermined time, the switch control circuit  30  temporarily turns off the low-side switch element  50  while keeping the high-side switch element  40  off. 
     That is, in a case where the currents to be supplied to the solenoids  110   a  and  110   b  are controlled by the PWM signals  11   a  and  11   b  each having a low duty ratio, in particular, by the PWM signals  11   a  and  11   b  each having a duty ratio corresponding to the instruction current value of the current “0”, if a certain time elapses in such a state, the low-side switch element  50  is temporarily turned off, and the current path in the reverse direction is cut off in advance in order to prevent the reverse current. If the PWM signals  11   a  and  11   b  indicating that the instruction current value is not “0” but is a certain value or more is received, the fixation of the low-side switch element  50  in the OFF state is released to return to the normal synchronous rectification operation in which either the high-side switch element  40  or the low-side switch element  50  is turned on. 
     As a result, the path of the reverse current of the solenoid is cut off by a simpler method, and feedback control can be continued for the solenoid capable of performing normal feedback control while preventing the occurrence of an unintended valve operation due to the flow of the reverse current. As a result, in the solenoid that controls disconnection of a lock-up clutch, it is possible to suppress the occurrence of a shift shock while preventing fastening of an unintended lock-up when a ground line is disconnected, for example. 
     Second Embodiment 
     The above first embodiment prevents the generation of the reverse current when the instruction current value is “0” or the instruction current value is extremely small. However, even when one solenoid  110   a  is controlled with a certain instruction current and another solenoid  110   b  is operating with an extremely large current, a reverse current is sometimes generated when the low-side switch element  50  of the solenoid  110   a  is in an ON state. Although the reverse current is controlled to be canceled by feedback control of a current supplied to the solenoid, such control usually requires several cycles or more in units of PWM cycles. Therefore, a function of negating the PWM signal  32  when a reverse current equal to or larger than a certain determination threshold is detected, temporarily turning off the low-side switch element  50 , and cutting off the reverse current may be added. This function can be installed in parallel with the function of preventing the generation of the reverse current when the instruction current value is “0” illustrated in the operation timing chart of  FIGS. 3 and 6  or when the instruction current value is extremely small. 
       FIG. 7  is a configuration diagram of a current control device for a vehicle automatic transmission according to a second embodiment of the present invention. 
     In the second embodiment, a comparator  71  that detects a reverse current equal to or larger than a certain current threshold Irev_th from a current value to the solenoid  110   a  obtained by the LS current measurement circuit  70  and a reverse current time measurement circuit  72  that measures a generation time (period) of the reverse current are added to the above first embodiment such that a result of the measurement is input to the switch control circuit  30  and is used for switch control (also referred to as gate control) for turning on and off the high-side switch element  40  and the low-side switch element  50 . 
     That is, as illustrated in an operation timing chart of  FIG. 8 , if the reverse current equal to or larger than the certain current threshold Irev_th is detected for a certain time threshold tDET_Irev or longer and it is detected that a current in the reverse direction from the normal direction flows through the low-side switch element  50  by a determination threshold (predetermined current) or more by using the comparator  71  and the reverse current time measurement circuit  72 , the PWM signal  32  is negated at that time, and the low-side switch element  50  is temporarily turned off by the switch control circuit  30  to cut off the reverse current. 
     Incidentally, the configuration illustrated in  FIG. 7  is an example, and other configurations may be adopted as long as it can be detected that the current in the reverse direction from the normal direction flows through the low-side switch element  50  by the predetermined current or more. 
     In this manner, according to the second embodiment, the LS current measurement circuit  70  that measures the current value supplied to the solenoid  110   a  is provided, and the switch control circuit  30  has a function of temporarily turning off the low-side switch element  50  while keeping the high-side switch element  40  off when the LS current measurement circuit  70  detects that the current in the reverse direction from the normal direction flows by the predetermined current or more. That is, in a case where a certain reverse current is detected when the low-side switch element  50  is turned on, the low-side switch element  50  is turned off to cut off a further current path in the reverse direction. 
     As a result, it is possible to reliably prevent the occurrence of an unintended valve operation due to the flow of the reverse current. As a result, in the solenoid that controls disconnection of a lock-up clutch, it is possible to suppress the occurrence of a shift shock while preventing fastening of an unintended lock-up when a ground line is disconnected, for example, which is similar to the first embodiment. 
     Incidentally, the present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail in order to describe the present invention in an easily understandable manner, and are not necessarily limited to one including the entire configuration that has been described above. In addition, some configurations of a certain embodiment can be substituted by configurations of another embodiment, and further, a configuration of another embodiment can be added to a configuration of a certain embodiment. 
     In addition, only a control line and a signal line considered to be necessary for the description have been illustrated, and all control lines and signal lines required for a product are not illustrated. 
     REFERENCE SIGNS LIST 
     
         
           10 ,  10   a ,  10   b  load drive circuit 
           11 ,  11   a ,  11   b  PWM signal 
           20  HS/LS control time measurement circuit (time measurement circuit) 
           30  switch control circuit 
           31  high-side switch element control PWM signal 
           32  low-side switch element control PWM signal 
           40  high-side switch element 
           50  low-side switch element 
           60  HS current measurement circuit 
           70  LS current measurement circuit 
           71  comparator 
           72  reverse current time measurement circuit 
           80  current calculation circuit 
           100  current control device 
           110 ,  110   a ,  110   b  solenoid 
           120  solenoid ground power source 
           150  battery power source 
           160  current control device ground power source 
           170  current control device ground connection node 
           200  microcontroller (microcomputer)