Abstract:
A motor-driving-circuit comprising: a first to-fourth-transistors; a drive-control-circuit to control a energization-state of a motor coil so as to be a driving-state where either one group of a groups of the first-and-fourth-transistors and the second-and-third-transistors is on and the other group is off, or so as to be a regeneration-state where the first-and-third-transistors are off and the second-and-fourth-transistors are on; a set-current-detection-circuit; an overcurrent-detection-circuit; and an overcurrent-protection-circuit to output a regeneration-instruction-signal for shifting the energization-state to the regeneration-state if an overcurrent-state does not occur and output a drive-stop-signal for stopping driving the coil if the overcurrent-state occurs, when a current amount flowing through the coil has reached a set-level in the driving-state, the drive-control-circuit shifting the energization-state to the regeneration-state to be maintained for a predetermined time period and thereafter returning the energization-state to the driving-state when the regeneration-instruction-signal is output, and turning off the first-to-fourth-transistors when the drive-stop-signal is output.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority to Japanese Patent Application No. 2009-3940, filed Jan. 9, 2009, of which full contents are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a motor driving circuit. 
         [0004]    2. Description of the Related Art 
         [0005]    Some motor driving circuits may keep the amounts of currents flowing through motor coils at set levels by controlling on and off of transistors connected to the motor coils (Japanese Patent Application Laid-Open Publication No. 2005-184897). For example, in a motor driving circuit shown in  FIG. 5 , an energization state of a motor coil M connected between terminals T 1  and T 2  is controlled by on and off of N-channel MOSFETs  110  to  113  making up an H-bridge. For example, in a drive control circuit  120 , the N-channel MOSFETs  110  and  113  are turned on and the N-channel MOSFETs  111  and  112  are turned off, so that the circuit passes the current through a path of the N-channel MOSFET  110 , the motor coil M, and the N-channel MOSFET  113 , to drive the motor (driving state). The amount of the current flowing through the motor coil M is detected by a resistor R connected via a terminal T 3  and when the amount of the current flowing through the motor coil M reaches the set level, the drive control circuit  120  turns off the N-channel MOSFET  110  and turns on the N-channel MOSFET  111 . As a result, the current, which the motor coil M tries to continue passing, is regenerated by a loop of the N-channel MOSFET  111 , the motor coil M, and the N-channel MOSFET  113 , and decreases gradually (regeneration state). As such, the drive control circuit  120  is capable of maintaining the amount of the current flowing through the motor coil M at the set level by repeating the driving state and the regeneration state. 
         [0006]    Incidentally, in the motor driving circuit, a load may be short-circuited due to aged deterioration of the motor, for example. In the motor driving circuit shown in  FIG. 5 , if the load is short-circuited, an overcurrent occurs in a case where the energization state of the motor coil M is the driving state, and if the overcurrent is over the set level of the current flowing through the motor coil M, the drive control circuit  120  changes the energization state of the motor coil M to the regeneration state. Then, after elapse of a predetermined time, the drive control circuit  120  changes the energization state of the motor coil M to the driving state, and the driving state and the regeneration state are repeated despite the load is short-circuited. Since the motor driving circuit is generally provided with an overheat protection function, circuit operation stops before causing circuit failure even if the driving state and the regeneration state are repeated in a state where the load is short-circuited. It is desirable, however, to detect a short circuit of the load and protect the circuit before it becomes in such an overheated state. 
       SUMMARY OF THE INVENTION 
       [0007]    A motor driving circuit according to an aspect of the present invention, comprises: a first transistor on a power source side and a second transistor on a ground side connected in series; a third transistor on the power source side and a fourth transistor on the ground side connected in series; a drive control circuit configured to control a energization state of a motor coil so as to be a driving state where either one group of a group of the first and fourth transistors and a group of the second and third transistors is on and the other group is off, or so as to be a regeneration state where the first and third transistors are off and the second and fourth transistors are on, the motor coil connected to a connection point of the first and second transistors and a connection point of the third and fourth transistors; a set current detection circuit configured to detect whether an amount of current flowing through the motor coil has reached a set level; an overcurrent detection circuit configured to detect an overcurrent state where an amount of current flowing through any of the first to fourth transistors is over a predetermined amount of current; and an overcurrent protection circuit configured to output a regeneration instruction signal for shifting the energization state to the regeneration state in a case where the overcurrent state does not occur and output a drive stop signal for stopping driving the motor coil in a case where the overcurrent state occurs, when the amount of current flowing through the motor coil has reached the set level in the driving state, the drive control circuit shifting the energization state to the regeneration state to be maintained for a predetermined time period and thereafter returning the energization state to the driving state when the regeneration instruction signal is output, and turning off the first to fourth transistors when the drive stop signal is output. 
         [0008]    Other features of the present invention will become apparent from descriptions of this specification and of the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    For more thorough understanding of the present invention and advantages thereof, the following description should be read in conjunction with the accompanying drawings, in which: 
           [0010]      FIG. 1  is a diagram of a configuration of a motor driving circuit according to an embodiment of the present invention; 
           [0011]      FIG. 2  is a timing chart of one example of an operation when a load is short-circuited; 
           [0012]      FIG. 3  is a timing chart of one example of an operation when a short circuit to a high voltage point occurs; 
           [0013]      FIG. 4  is a timing chart of one example of an operation when a short circuit to ground occurs; and 
           [0014]      FIG. 5  is a diagram of a configuration example of a general motor driving circuit. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    At least the following details will become apparent from descriptions of this specification and of the accompanying drawings.  FIG. 1  is a diagram of a configuration of a motor driving circuit  10  according to an embodiment of the present invention. The motor driving circuit  10  includes N-channel MOSFETs  20  to  23 , a drive control circuit  30 , comparators  32  to  36 , reference sources  40  to  42 , NAND circuits  45  though  52 , an AND circuit  54 , NOR circuits  56  and  57 , a NOT circuit  58 , counters  60  and  61 , and a SR flip-flop  63 . 
         [0016]    The N-channel MOSFETs  20  to  23  make up an H-bridge circuit, and a motor coil M is connected, via terminals T 1  and T 2 , between a connection point of the N-channel MOSFET  20  (first transistor) and the N-channel MOSFET  21  (second transistor) and a connection point of the N-channel MOSFET  22  (third transistor) and the N-channel MOSFET  23  (fourth transistor). The motor coil M is a DC motor coil, for example, and current flows through the motor coil M in a direction from the terminal T 1  to the terminal T 2  so as to rotate a motor in a positive direction (positive rotation) and the current flows through the motor coil M in a direction from the terminal T 2  to the terminal T 1  so as to rotate the motor in a reverse direction (reverse rotation). 
         [0017]    The drive control circuit  30  controls on and off of the N-channel MOSFETs  20  to  23  so that the amount of the current flowing through the motor coil M reaches a set level, according to the direction of the motor rotation. For example, in the case of the positive rotation, the drive control circuit  30  firstly turns on the N-channel MOSFETs  20  and  23  and turns off the N-channel MOSFETs  21  and  22 . Thus, the current flows through a path of the N-channel MOSFET  20 , the motor coil M, and the N-channel MOSFET  23 . A state in which the current flows through this path is referred to as a driving state. When the amount of the current flowing through the motor coil M reaches a set level, the drive control circuit  30  turns off the N-channel MOSFET  20  and turns on the N-channel MOSFET  21 . Thus, the current flowing through the motor coil M is regenerated in a loop of the N-channel MOSFET  21 , the motor coil M, and the N-channel MOSFET  23 . A state in which the current flows through this path is referred to as a regeneration state. In the case of the reverse rotation, the current flows through the path of the N-channel MOSFET  22 , the motor coil M, and the N-channel MOSFET  21  in the driving state, and the current flows in the loop of the N-channel MOSFET  23 , the motor coil M, and the N-channel MOSFET  21  in the regeneration state. Furthermore, when detecting overcurrent caused by a short circuit to a high voltage point, a short circuit to ground, or a short circuit of a load, the drive control circuit  30  turns off all of the N-channel MOSFETs  20  to  23 . 
         [0018]    The comparator  32  is a circuit for detecting whether the amount of the current flowing through the motor coil M has reached the set level when the motor coil M is in the driving state. Specifically, the comparator  32  outputs a comparison result of a voltage Vrf generated by the current flowing through a resistor R connected via the terminal T 3  and a reference voltage Vref 1  according to the set level output from the reference source  40 . 
         [0019]    The comparator  33  and the NAND circuit  45  make up an overcurrent detection circuit for detecting whether the current flowing through the N-channel MOSFET  20  is the overcurrent. In an embodiment according to the present invention, a voltage Vm-Vref 2  that is lower by a reference voltage Vref 2  of the reference source  41  than the power source Vm is applied to a positive input terminal of the comparator  33 . A negative input terminal of the comparator  33  is connected to the source of the N-channel MOSFET  20 . Therefore, in a state where a signal N 1  goes high and the N-channel MOSFET  20  is turned on, if the overcurrent occurs in the N-channel MOSFET  20  due to the short circuit of the terminal T 1  to the ground or occurrence of the short circuit of the load, for example, a voltage drop occurs in the N-channel MOSFET  20  becomes greater than Vref 2 , the output of the comparator  33  goes high, and the output of the NAND circuit  45  goes low. Similarly, the comparator  34  and the NAND circuit  46  make up an overcurrent detection circuit for detecting whether the current flowing through the N-channel MOSFET  22  is the overcurrent. 
         [0020]    The comparator  35  and the NAND circuit  47  make up an overcurrent detection circuit for detecting whether the current flowing through the N-channel MOSFET  21  is not overcurrent. In an embodiment according to the present invention, the positive input terminal of the comparator  35  is connected to the drain of the N-channel MOSFET  21  and the negative input terminal of the comparator  35  is applied with a voltage which is higher by a reference voltage Vref 3  of the reference source  42  than the voltage of the source of the N-channel MOSFET  21 . Therefore, in a state where a signal N 2  goes high and the N-channel MOSFET  21  is turned on, if the overcurrent occurs in the N-channel MOSFET  21  due to the short-circuit of the terminal T 1  to a high voltage point, for example, the voltage drop occurs in the N-channel MOSFET  21  becomes greater than Vref 3 , the output of the comparator  35  goes high, and the output of the NAND circuit  47  goes low. Similarly, the comparator  36  and the NAND circuit  48  make up an overcurrent detection circuit for detecting whether the current flowing through the N-channel MOSFET  23  is the overcurrent. 
         [0021]    The output signals of the NAND circuits  45  to  48  are input to the AND circuit  54 . Therefore, if the overcurrent occurs in any of the N-channel MOSFETs  20  to  23 , then any of the outputs of the NAND circuits  45  to  48  goes low so that the output of the AND circuit  54  goes low. 
         [0022]    To the NAND circuit  49 , the signal N 1  to be input to the gate of the N-channel MOSFET  20  and a signal for instructing the positive rotation or reverse rotation, which is input from an input terminal IN 1 , are input. To the NAND circuit  50 , the signal N 3  to be input to the gate of the N-channel MOSFET  22  and a signal obtained by inverting by the NOT circuit  58  the signal input from an input terminal IN 1  are input. In an embodiment according to the present invention, the signal input from the input terminal IN 1  goes high in the case of the positive rotation and goes low in the case of the reverse rotation. Therefore, in the case of the positive rotation, the output of the N-channel MOSFET  50  is always high and the output of the N-channel MOSFET  49  is low only during a time period in which the signal N 1  is high. Similarly, in the case of the reverse rotation, the output of the N-channel MOSFET  49  is always high and the output of the N-channel MOSFET  50  is low only during a time period in which the signal N 3  is high. Since the output signals of the NAND circuits  49  and  50  are input to the NAND circuit  51 , the output of the NAND circuit  51  is high when the energization state of the motor coil M is the driving state, in either case of the positive rotation or the reverse rotation. 
         [0023]    The counter  60  (minimum time count circuit) is a circuit for counting the minimum time of a time during which the energization state of the motor coil M is the driving state. In an embodiment of the present invention, when the energization state of the motor coil M becomes the driving state, the output of the NAND circuit  51  goes high. Therefore, the counter  60  starts counting when the output of the NAND circuit  51  goes high, and changes the level of the output signal to the high level when a count value reaches a value corresponding to the minimum time. The count value of the counter  60  is reset when the output of the NAND circuit  51  goes low. 
         [0024]    The counter  61  is a circuit for counting a mask time from a time when the overcurrent is detected until a time when a state is shifted to a protective state. In an embodiment of the present invention, the output signal of the AND circuit  54  and the output signal from an output terminal Q of the SR flip-flop  63  are input to the NOR circuit  56 , and when both of these two signals go low, the output of the NOR circuit  56  goes high. The counter  61  starts counting when the output of the NOR circuit  56  goes high and changes the level of its output signal to the low level when a count value reaches a value corresponding to the mask time. The count value of the counter  61  is reset when the output of the NOR circuit  56  goes low before the count value reaches the value corresponding to the mask time. When the output signal of the counter  61  goes low, the drive control circuit  30  determines the presence of the overcurrent state and turns off all of the N-channel MOSFETs  20  to  23 . Here, the low-level signal output from the counter  61  is one example of a drive stop signal according to the present invention. 
         [0025]    In the SR flip-flop  63 , the output signal of the counter  61  is input to the inverting set terminal /S thereof and the signal input from the input terminal IN 2  is input to its inverting reset terminal /R thereof. Therefore, when the signal input to the inverting set terminal /S goes low, the signal output from the output terminal Q goes high and the signal output from the inverting output terminal /Q goes low, and when the signal input to the inverting reset terminal /R goes low, the signal output from the output terminal Q goes low and the signal output from the inverting output terminal /Q goes high. The signal input from the input terminal IN 2  goes low at the time of start-up of the motor driving circuit  10  and thereafter maintains the high level. Therefore, the signals output from the output terminal Q and the inverting output terminal /Q of the SR flip-flop  63  are low and high, respectively, at the initial state. Thereafter, when the signal output from the counter  61  goes low, the signals output from the output terminal Q and the inverting output terminal /Q of the SR flip-flop  63  go high and low, respectively. 
         [0026]    The output signal of the counter  60 , the output signal of the AND circuit  54 , and the signal output from the inverting output terminal /Q of the SR flip-flop  63  are input to the NAND circuit  52 . Therefore, only when all of these three signals are high, the output signal of the NAND circuit  52  goes low. The signal output from the NAND circuit  52  and the signal output from the comparator  32  are input the NOR circuit  57 . Therefore, only when both of these two signals are low, the signal output from the NOR circuit  57  goes high. When the signal output from the NOR circuit  57  goes high in a case where the energization state of the motor coil M is the driving state, the drive control circuit  30  changes the energization state to the regeneration state. Here, the high-level signal output from the NOR circuit  57  is one example of a regeneration instruction signal according to the present invention. 
         [0027]    The circuit including the NAND circuits  49  to  52 , the NOR circuits  56  and  57 , the NOT circuit  58 , the counters  61  and  62 , and the SR flip-flop  63  correspond to one example of an overcurrent protection circuit according to the present invention. 
         [0028]      FIG. 2  is a timing chart of one example of an operation when the load is short-circuited. It is assumed that the short circuit of the load does not occur in the initial state. At the beginning, all of the signals N 1  to N 4  input to the gates of the N-channel MOSFETs  20  to  23  are low and the N-channel MOSFETs  20  to  23  are off. 
         [0029]    Thereafter, at a time T 1 , when the signals N 1  and N 4  go high, the energization state of the motor coil M is changed to the driving state and the amount of the current flowing though the motor coil M increases. When the signal N 1  goes high, the counter  60  starts counting; and at a time T 2 , when a count value reaches a value corresponding to the minimum time of the driving state at a time T 2 , the signal B output from the counter  60  goes high. At this time, since the overcurrent does not occur, the signal A output from the AND circuit  54  is high, and since the SR flip-flop  63  is in the initial reset state, the signal D output from the inverting output terminal /Q is also high. Therefore, all of the signals A, B, and D input to the NAND circuit  52  are high and the signal E output from the NAND circuit  52  is changed to the low level. 
         [0030]    Thereafter, the amount of the current flowing through the motor coil M continues to increase and at a time T 3 , when it reaches the set level set by the power source  40 , the signal F output from the comparator  32  is changed to the low level. At this time, since the signal E is also low, both of the signals E and F input to the NOR circuit  57  are low and the signal G output from the NOR circuit  57  is changed to the high level. 
         [0031]    When the signal G goes high, the drive control circuit  30  determines that the amount of the current flowing through the motor coil M has reached the set level, and at a time T 4 , allows the signal N 1  to be changed to the low level and the signal N 2  to be changed the high level, and thus, the energization state of the motor coil M is changed to the regeneration state. Due to the signal N 1  being changed to the low level, the counter  60  is reset and the signal B is changed to the low level. Due to the signal B being changed to the low level, the signal E goes high and the signal G goes low. 
         [0032]    After elapse of a predetermined time of the regeneration state, the drive control circuit  30  allows the signal N 1  to be changed to the high level and the signal N 2  to be changed to the low level at a time T 5 . Thus, the energization state of the motor coil M is changed again to the driving state. At this time, if it is assumed that the short circuit of the load occurs, the amount of the current flowing through the motor coil M rapidly increases. At a time T 6 , when the amount of the current flowing through the motor coil M reaches the set level, the signal F is changed to the low level. Furthermore, the short circuit of the load causes the overcurrent in the N-channel MOSFET  20  or the N-channel MOSFET  23 , and thus the signal A is changed to the low level at time T 7 . 
         [0033]    When the signal N 1  goes high, the counter  60  starts counting and the signal B is changed to the high level at a time T 8 . At this time, out of the signals A, B, and D input to the NAND circuit  52 , the signals B and D are high, however, the signal A is low due to the occurrence of the overcurrent. Therefore, the signal E remains high and the signal G remains low. As a result, although the amount of the current flowing through the motor coil M has reached the set level, the signal G remains low, and thus, the drive control circuit  30  keeps the energization state of the motor coil M in the driving state. 
         [0034]    When the signal A goes low, the signal output from the NOR circuit  56  goes high and the counter  61  starts counting. Thereafter, at a time T 9 , when the count value of the counter  61  reaches the count value corresponding to the mask time, the signal C is changed to the low level. When the signal C goes low, the drive control circuit  30  determines that the signal A is low because of the occurrence of the overcurrent not because of the effect of the noises, etc., and allows all of the signals N 1  to N 4  to be changed to the low level. As a result, the motor coil M stops driving and the overcurrent state is eliminated. 
         [0035]      FIG. 3  is a timing chart of one example of an operation when the short circuit to the high voltage point occurs. Here, it is assumed that the terminal T 1  is short-circuited to the high voltage point. In the initial state, all of the signals N 1  to N 4  are low and the drive control circuit  30  allows the signals N 1  and N 4  to be changed to the high level at a time T 11 . Thus, the energization state of the motor coil M is changed to the driving state. As in the case of  FIG. 2 , the signal B goes high and the signal E goes low at a time T 12  and the signal F goes low and the signal G goes high at a time T 13 . 
         [0036]    When the signal G goes high, the drive control circuit  30  allows the signal N 1  to be changed to the low level and the signal N 2  to the high level at a time T 14 , as in the case of  FIG. 2 . As a result, the N-channel MOSFET  21  is turned on, however, since the terminal T 1  is short-circuited to the high voltage point, the overcurrent occurs in the N-channel MOSFET  21 . Therefore, the signal F goes low at a time T 15  and the signal A goes low at a time T 16 . After elapse of the mask time from the time T 16 , the signal C is changed to the low level at a time T 17 . As at result, the drive control circuit  30  allows the signals N 1  to N 4  to be changed to the low level and the overcurrent state is eliminated. 
         [0037]      FIG. 4  is a timing chart of one example of an operation when the short circuit to the ground occurs. Here, it is assumed that the terminal T 1  is short-circuited to the ground. In the initial state, all of the signals N 1  to N 4  are low, and at a time T 21 , the drive control circuit  30  allows the signals N 1  and N 4  to be changed to the high level. As a result, the N-channel MOSFET  20  is turned on, however, since the terminal T 1  is short-circuited to the ground, the overcurrent occurs in the N-channel MOSFET  20 . At this time, the signal F remains high since no current flows through the resistor R, however, the signal A is changed to the low level at a time T 22  since the overcurrent occurs in the N-channel MOSFET  20 . 
         [0038]    Thereafter, as in the case of  FIG. 2 , the signal B is changed to the high level and the signal E is changed to the low level at a time  23 . Then, when the mask time has passed since the signal A went low, the signal C is changed to the low level at a time T 24 . As a result, the drive control circuit  30  allows all of the signals N 1  to N 4  to be changed to the low level and the overcurrent state is eliminated. 
         [0039]    As above, in the motor driving circuit  10  according to an embodiment of the present invention, when the amount of the current flowing through the motor coil M has reached the set level, it is shifted to the regeneration state in the case where the overcurrent does not occur, and it is not changed to the regeneration state but the overcurrent protection function is performed in the case where the overcurrent occurs. Therefore, when the load is short-circuited, there is no repetition of the driving state and the regeneration state, and thus safety when the load is short-circuited may be improved. In the motor driving circuit  10 , the overcurrent protection function is performed not only in the case of the short circuit of the load but also in the case of the short circuit to the high voltage point and the short circuit to the ground. 
         [0040]    In the motor driving circuit  10 , the mask time of the overcurrent is set by the counter  61 . Therefore, it becomes possible to control stop of the drive of the motor coil M, when noise is caused in the signal A, for example. 
         [0041]    In the motor driving circuit  10 , the minimum time in the driving state is set by the counter  60 , and even in such a configuration, the overcurrent protection function may appropriately be performed in any case of the short circuit of the load, the short circuit to the high voltage point, or the short circuit to the ground. 
         [0042]    The above embodiments of the present invention are simply for facilitating the understanding of the present invention and are not in any way to be construed as limiting the present invention. The present invention may variously be changed or altered without departing from its spirit and encompass equivalents thereof.