Patent Publication Number: US-2007097587-A1

Title: Inductive load drive device and drive method

Description:
BACKGROUND OF THE INVENTION  
      1. Field of Invention  
      The present invention relates to technology for shortening the regenerative current attenuation time and reducing capacitance between the power supply and ground in an inductive load drive circuit that can drive an inductive load in a single direction or in both normal and reverse directions.  
      2. Description of Related Art  
      Inductive load drive devices are used, for example, to drive the mechanical shutter in digital cameras, and shortening the time required for forward/reverse phase switching of the inductive load is desired. Reducing the forward/reverse phase switching time requires shortening the attenuation time of the regenerative current that is produced in the inductive load when the phase is switched. Japanese Unexamined Patent Appl. Pub. H5-268036 teaches an inductive load drive circuit that addresses this problem as described below with reference to  FIG. 19 .  
      The inductive load drive circuit shown in  FIG. 19  has a power supply  6   p,  a capacitance  7   p  between the power supply and ground, a high potential side transistor  101   p,  low potential side diode  102   p,  high potential side diode  103   p,  low potential side transistor  104   p,  output drive transistor control circuit  205   p,  and inductive load  8   p.  Operation of this inductive load drive circuit is described next.  
      The output drive transistor control circuit  205   p  first turns the high potential side transistor  101   p  and low potential side transistor  104   p  on. When the high potential side transistor  101   p  and low potential side transistor  104   p  then turn off simultaneously, the energy stored in the inductive load  8   p  is attenuated by flowing as a regenerative current through the low potential side diode  102   p,  inductive load  8   p,  and high potential side diode  103   p  to the power supply  6   p.    
      This attenuation time Tp is defined as: 
 
 Tp=Lp/Vp×Ip  
 
 where Lp is the inductance of the inductive load  8   p,  Vp is the voltage applied to both ends of the inductive load  8   p,  and Ip is the current flowing to the inductive load  8   p  while the transistors  101   p  and  104   p  are on. As this equation shows, increasing the terminal voltage Vp of the inductive load  8   p  can decrease the attenuation time Tp. 
 
      In Japanese Unexamined Patent Appl. Pub. H5-268036, 
 
 Vp =(voltage of power supply 6 p )+(forward voltage of low potential side diode 102 p )+(forward voltage of high potential side diode 103 p ) 
 
 and the terminal voltage Vp of the inductive load  8   p  can be increased. As a result, an inductive load drive device that can shorten the regenerative current attenuation time can be provided. 
 
      As electronic devices continue to become smaller, reducing the size of all components, including external components, has become increasingly important. The inductive load drive device taught in Japanese Unexamined Patent Appl. Pub. H5-268036 shortens the attenuation time by passing the regenerative current to the power supply  6   p.  The power supply  6   p  normally has no ability to pull current, and therefore uses an internal resistance  306   p  to transiently boost the power supply  6   p  voltage as shown in  FIG. 19 . The power supply voltage can therefore exceed the withstand voltage of the inductive load drive device and possibly damage the drive device. To avoid such damage, the capacitance of the power supply—ground capacitance  7   p  must be set high to suppress an increase in the power supply voltage. This necessarily increases the physical size of the supply-ground capacitance  7   p  and makes incorporating the inductive load drive device in small electronic devices, particularly cell phones, difficult.  
     SUMMARY OF THE INVENTION  
      The present invention therefore shortens the attenuation time of the regenerative current that is produced in the inductive load during phase switching without increasing the capacitance between the power supply and ground.  
      An inductive load drive device according to a first aspect of the invention is a device operable to drive an inductive load by repeatedly switching between a drive state supplying drive power to the inductive load and a regeneration state in which regenerative power from the inductive load is received, and has a drive signal generator operable to generate a drive signal denoting a logic level of the drive state and the regeneration state, and a driver that is controlled based on the drive signal to an OFF state, a high resistance ON state having a high on resistance, or a low resistance ON state having a low on resistance operable to generate the drive power. The driver has a high potential side switching unit group having at least one switching unit, and a low potential side switching unit group having at least one switching unit. When in the regeneration state, the switching unit group of the high potential side switching unit group or the low potential side switching unit group is controlled to the OFF state and at least one switching unit of the other switching unit group is controlled to the high resistance ON state.  
      An inductive load drive method according to another aspect of the invention is a method operable to drive an inductive load by repeatedly switching between a drive state supplying drive power to the inductive load and a regeneration state receiving regenerative power from the inductive load by a high potential side switching unit group having at least one switching unit and a low potential side switching unit group having at least one switching unit, and has steps of: generating a drive signal denoting a logic level of the drive state and the regeneration state, generating the drive power controlled to an OFF state, a high resistance ON state having a high ON resistance, or a low resistance ON state having a low ON resistance based on the drive signal, and turning the switching unit group of the high potential side switching unit group or the low potential side switching unit group off and setting at least one switching unit of the other switching unit group to the high resistance ON state when in the regeneration state.  
      The regenerative current does not flow to the power supply side with the inductive load drive device and drive method of the invention, and the power supply voltage is therefore not increased by inflowing current even when there is an internal resistance in the power supply. The withstand voltage of the inductive load drive device can therefore be designed without an extra safety margin, the size of the capacitance between the power supply and ground can therefore be reduced, and the cost can therefore be reduced. The attenuation time of the regenerative current can therefore be shortened, the regeneration state can be minimized, and the forward/reverse phase switching time of the inductive load can be shortened.  
      More specifically, controlling the on resistance of the transistor enables increasing the resistance of the regenerative current path and enables shortening the regenerative current attenuation time because the current consumption time of the path resistance is shortened.  
      Furthermore, because transistor on resistance can be feedback controlled to maximize the drain voltage while not exceeding the withstand voltage of the inductive load drive device, the resistance of the regenerative current path can be maximized more appropriately and the regenerative current attenuation time can be shortened even more because this path resistance shortens the power consumption time.  
      In addition, the resistance of the regenerative current path can be increased by selectively using a high ON resistance transistor in the regeneration state, and the regenerative current attenuation time can be shortened even more because this path resistance shortens the power consumption time.  
      Yet further, by selecting the number of transistors that are on in the regenerative current path, the path resistance can be increased and the regenerative current attenuation time can be further shortened because this path resistance shortens the power consumption time.  
      The regenerative current attenuation time can be yet further shortened by monitoring regenerative current attenuation and switching to the reverse phase drive state as soon as attenuation is completed.  
      Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic block diagram of an inductive load drive device according to a first embodiment of the invention.  
       FIG. 2  describes the current path in an inductive load drive device according to a first embodiment of the invention.  
       FIG. 3  is a timing chart describing the operation of the drive unit in an inductive load drive device according to a first embodiment of the invention.  
       FIG. 4  is a schematic block diagram of an inductive load drive device according to a second embodiment of the invention.  
       FIG. 5  is a timing chart describing the operation of the drive unit in an inductive load drive device according to a second embodiment of the invention.  
       FIG. 6  is a schematic block diagram of an inductive load drive device according to a third embodiment of the invention.  
       FIG. 7  is a partial circuit diagram describing the operation of an inductive load drive device according to a third embodiment of the invention.  
       FIG. 8  is a timing chart describing the operation of the drive unit in an inductive load drive device according to a third embodiment of the invention.  
       FIG. 9  is a schematic block diagram of an inductive load drive device according to a fourth embodiment of the invention.  
       FIG. 10  is a schematic block diagram of an inductive load drive device according to a fifth embodiment of the invention.  
       FIG. 11  is a schematic block diagram of an inductive load drive device according to a sixth embodiment of the invention.  
       FIG. 12  is a timing chart describing the operation of the drive unit in an inductive load drive device according to a sixth embodiment of the invention.  
       FIG. 13  is a schematic block diagram of an inductive load drive device according to a seventh embodiment of the invention.  
       FIG. 14  is a schematic block diagram of an inductive load drive device according to an eighth embodiment of the invention.  
       FIG. 15  is a schematic block diagram of an inductive load drive device according to a ninth embodiment of the invention.  
       FIG. 16  is a schematic block diagram of an inductive load drive device according to a tenth embodiment of the invention.  
       FIG. 17  is a partial circuit diagram describing the operation of an inductive load drive device according to a tenth embodiment of the invention.  
       FIG. 18  is a timing chart describing the operation of the drive unit in an inductive load drive device according to a tenth embodiment of the invention.  
       FIG. 19  is a schematic block diagram showing the arrangement of an inductive load drive device according to the related art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Preferred embodiments of the present invention are described below with reference to the accompanying figures. Numeric values used in the following description of the invention are used by way of example to better describe the invention, and the invention is not limited to these values.  
     First Embodiment  
       FIG. 1  is a schematic block diagram of an inductive load drive device according to a first embodiment of the invention.  
      An inductive load drive device according to the present invention supplies drive power to an inductive load  8 .  
      The period when drive power is supplied is called the “drive period” below, and the operating state at that time is called the “drive state.” 
      The period when supplying drive power stops and regenerative power from the inductive load  8  is received is called the “regeneration period,” and the operating state at that time is called the “regeneration state.” 
      An inductive load drive device according to the invention is a device for driving an inductive load  8  by repeatedly switching between the drive state supplying drive power to the inductive load  8 , and the regeneration state receiving drive power from the inductive load  8 .  
      The inductive load drive device shown in  FIG. 1  has a drive unit  10  for supplying drive power to the inductive load  8 , a predriver unit  5 , a power supply  6 , a ground  2 , a capacitance between the power supply and ground  7 , an internal resistance  306  in the power supply, and a state signal generating unit  3  that outputs a state signal S 3  indicating whether the current operating state is the drive state or regeneration state. A delay processing unit  152  generates a delay processing signal S 152  that goes high for a predetermined regeneration period starting from when the state signal S 3  switches from the drive state to the regeneration state.  
      The drive unit  10  includes a high potential side switching unit  11  and low potential side switching units  12  and  1 . The low potential side switching unit  1  has a regeneration switching function. The high potential side switching unit  11  renders a high potential side switching unit group, and the low potential side switching units  12  and  1  together render a low potential side switching unit group. Each switching unit  11 ,  12 ,  1  has a body diode parallel connected in reverse conductivity. Switch  13  switches the gate voltage S 12 G of the low potential side switching unit  12 , and switch control unit  4  generates the switch control signal S 4  that controls switch  13  and the gate voltage S 1 G of the low potential side switching unit  12 . The switch control unit  4  generates the switch control signal S 4  by taking the logical product of the delay processing signal S 152  and the inverse of the state signal S 3 . The switch  13  selects the output of the predriver unit  5  when the switch control signal S 4  is LOW, and selects the regenerative gate voltage source  151  when the switch control signal S 4  is HIGH.  
      The state signal generating unit  3 , delay processing unit  152 , predriver unit  5 , switch control unit  4 , switch  13 , and regenerative gate voltage source  151  render a drive signal generating unit. The gate voltages S 11 G, S 1 G, and S 12 G applied by the drive signal generating unit are collectively called the drive signal. The drive signal represents the logic level of the drive state and regeneration state.  
      The switching units  11 ,  12 , and  1  in this embodiment of the invention are MOS transistors, bipolar transistors, IGBT (insulated gate bipolar transistors), or other type of circuit that can be switched by a applying a control signal. An n-channel MOS transistor is used for the low potential side switching unit, and a p-channel MOS transistor is used for the high potential side switching unit in this embodiment of the invention. In this case the control node of the switching unit is the gate, the first main node is the drain, and the second main node is the source. The voltage applied to the control node is the gate voltage, the voltage at the first main node is the drain voltage, and the voltage at the second main node is the source voltage.  
      The operation of this inductive load drive device is described next with reference to  FIG. 1  and  FIG. 2 .  FIG. 3  is a timing chart of the signals in this inductive load drive device.  
      In the drive state the state signal S 3  is HIGH, the delay processing signal S 152  is LOW, the gate voltage S 11 G of the high potential side switching unit  11  goes LOW, and the high potential side switching unit  11  is therefore ON. The switch control signal S 4  goes LOW during the drive state, the gate voltage S 1 G of the low potential side switching unit  1  goes LOW, and the low potential side switching unit  1  is therefore OFF. The switch  13  switches to the predriver unit  5  side, and the low potential side switching unit  12  goes ON. As indicated by solid line arrow R 1  in  FIG. 2 , the drive current therefore flows through the drive current path from the power supply  6  through the high potential side switching unit  11 , inductive load  8 , low potential side switching unit  12 , and to ground  2 . This path of drive current flow is called the “drive current path” below.  
      To stop driving and change to the regeneration state from the drive state, the state signal S 3  goes from HIGH to LOW and the high potential side switching unit  11  turns OFF. The characteristics of the inductive load  8  cause regenerative current to continue flowing to the inductive load  8  until the energy stored during the drive period is completely discharged. Because the delay processing signal S 152  goes HIGH for the predetermined regeneration period starting from when the state signal S 3  switches to the regeneration state, the switch control signal S 4  goes HIGH, the low potential side switching unit  1  is ON, and the switch  13  is connected to the regenerative gate voltage source  151 .  
      The change in the regenerative current I(t) flowing to the inductive load  8  at time t in the regeneration state is represented by equation (1) 
 
 dl ( t )/ dt=−Vd/L  
 
 Vd=R on× I ( t )   (1) 
 
 and the regenerative current I(t) is therefore represented by equation (2) 
 
 I ( t )=( I max)×(exp(− R on/ L×t ))   (2) 
 
 where Imax is the maximum current flow through the inductive load  8  during the drive period, L is the inductance of the inductive load  8 , Ron is the on resistance of the low potential side switching unit  12 , and Vd is the drain-source voltage of the low potential side switching unit  12 . The time required for I(t) to become sufficiently small, such as 1/100, can be derived from equation (2), and the regeneration period of the delay processing unit  152  can be set based on this time. 
 
      In the regeneration state the gate voltage S 12 G of the low potential side switching unit  12  is regenerative gate voltage S 151 , which is a lower voltage than the state signal S 3 , and the on resistance Ron of the low potential side switching unit  12  therefore rises. The ON state in which the on resistance of the switching unit is high is called the “high resistance ON state,” and the ON state in which the on resistance of the switching unit is low is called the “low resistance ON state.” The state when the gate voltage of the switching unit is sufficiently high is called the “full ON state,” and the state in which the switching unit gate voltage is, like the regenerative gate voltage S 151 , lower than in the full ON state is the “half ON state.” The full ON state and half ON state are collectively referred to simply the ON state.  
      As indicated by imaginary line arrow R 2  in  FIG. 2 , the regenerative current flows through the regenerative current path from ground  2  to the low potential side switching unit  1  in the low resistance ON state of the full ON mode, the inductive load  8 , the low potential side switching unit  12  in the high resistance ON state of the half ON mode, and back to ground  2 . This path through which the regenerative current flows is called the regenerative current path. Because no part of the regenerative current path flows to the power supply  6 , the supply-to-ground capacitance  7  can be low. In addition, because the ON resistance of the low potential side switching unit  12  is high, the voltage at both ends of the inductive load  8  can be set high and the time required for regenerative current attenuation can be shortened. When the predetermined regeneration period of the delay processing unit  152  ends, the switch control signal S 4  goes LOW and the low potential side switching unit  1  therefore turns off. The switch  13  also selects output from the predriver unit  5  and outputs low, and the low potential side switching unit  12  therefore turns off. That is, the drive unit  10  stops. When the state signal S 3  then goes HIGH again, the drive state is resumed.  
      The method of setting the regenerative gate voltage S 151  is described below. If Vs is the voltage of the power supply  6 , Vf is the normal forward voltage of the body diode of the high potential side switching unit  11 , Imax is the maximum current flow through the inductive load  8  in the drive period, and Ron is the on resistance of the low potential side switching unit  12 , then Ron is set so that equation (3) is true. 
 
 I max)×( R on)&lt; Vs+Vf    (3) 
 
 The regenerative gate voltage S 151  is then set based on the relationship between the ON resistance Ron and gate voltage S 12 G of the low potential side switching unit  12 . The greatest ON resistance Ron that satisfies equation (3) is selected in order to minimize the attenuation time. The relationship between the ON resistance Ron and gate voltage S 12 G greatly depends on the size and process of the switching unit that is used, and description thereof is thus omitted here. 
 
      Equation (3) also assumes that 
 
 V max&gt; Vs+Vf  
 
 is true where Vmax is the withstand voltage of the used components. If 
 
 V max&lt; Vs+Vf  
 
 then equation (3) is 
 
( I max)×( R on)&lt; V max.   (4) 
 
 Substituting actual values into the above equations, if parts with a 5-V withstand voltage are used, the drive current during the drive state is 200 mA. If the regenerative gate voltage source  151  sets the ON resistance Ron of the low potential side switching unit  12  to 25 Ω, the regenerative current can be quickly attenuated without exceeding the withstand voltage.  FIG. 3  describes the change over time in the gate voltage of each switching unit in the drive unit  10 . The drain voltage S 12 D of the low potential side switching unit  12  decreases as the regenerative current attenuates. 
 
      An inductive load drive device according to this aspect of the invention thus turns the high potential side switching unit  11  off during the regeneration state to prevent regenerative current flow to the power supply  6 . As a result, the power supply voltage will not rise due to current inflow even if an internal resistance  306  is present in the power supply. An extra safety margin is therefore not required when setting the withstand voltage of the inductive load drive device and the size of the supply-to-ground capacitance  7  can therefore be reduced, thus affording a low unit cost. The regeneration period can also be shortened because the regenerative current attenuation time can be shortened.  
      More specifically, the resistance of the regenerative current path can be increased by controlling the ON resistance of the low potential side switching unit, the power consumption time is shortened by the path resistance, and the regenerative current attenuation time can be shortened.  
      The high potential side switching unit  11  is a p-channel MOS transistor in this embodiment of the invention, but the same effect can be achieved using an n-channel MOS transistor instead. The switch control unit  4  and predriver unit  5  are preferably logic circuits as shown in  FIG. 1 , but other devices that operate as described above can be used instead.  
     Second Embodiment  
       FIG. 4  is a schematic block diagram of an inductive load drive device according to a second embodiment of the invention. The first embodiment described above can drive the inductive load  8  in only one direction. This second embodiment differs in being able to drive the inductive load  8  in both forward and reverse directions. This embodiment is described below with particular reference to the differences between this embodiment and the first embodiment.  
      Shown in  FIG. 4  are the inductive load  8 , a drive unit  10  for supplying drive power to the inductive load  8 , predriver units  5 A and  5 B, a power supply  6 , a ground  2 , a capacitance between the power supply and ground  7 , an internal resistance  306  in the power supply, and a phase signal generating unit  9  for generating a phase signal S 9  representing forward or reverse phase state information. A state signal generating unit  3  outputs a state signal S 3  indicating whether the current operating state is the drive state or regeneration state. The state signal S 3  goes HIGH for a predetermined regeneration period starting when the phase signal S 9  changes phase.  
      The drive unit  10  includes high potential side switching units  11 A and  11 B, and low potential side switching units  12 A and  12 B. The high potential side switching units  11 A and  11 B together render a high potential side switching unit group, and the low potential side switching units  12 A and  12 B together render a low potential side switching unit group. Each switching unit  11 A,  11 B,  12 A,  12 B has a body diode parallel connected in reverse conductivity. Similarly to the first embodiment, the low potential side switching units  12 A and  12 B have a regeneration switching function.  
      Switches  13 A and  13 B switch the gate voltage S 12 AG, S 12 BG of the low potential side switching units  12 A and  12 B. The switch control unit  4  generates the switch control signals S 4 A and S 4 B that control the switches  13 A and  13 B, respectively. When the switch control signal S 4 A, S 4 B is LOW, the corresponding switch  13 A and  13 B selects the output from the predriver units  5 A and  5 B, and selects the regenerative gate voltage source  151 A,  151 B when the switch control signal S 4 A and S 4 B is HIGH.  
      The phase signal generating unit  9 , state signal generating unit  3 , predriver units  5 A and  5 B, switch control unit  4 , switches  13 A and  13 B, and regenerative gate voltage source  151 A,  151 B together render a drive signal generating unit. The gate voltages S 11 AG, S 11 BG, S 12 AG, and S 12 BG applied by the drive signal generating unit are collectively called the drive signal. The drive signal represents the logic level of the drive state and regeneration state.  
      The operation of this inductive load drive device during phase switching is described next with reference to  FIG. 4 .  FIG. 5  is a timing chart of the signals during this operation.  
      In the normal phase (forward) drive state the phase signal S 9  and state signal S 3  are LOW, the high potential side switching unit  11 A is on, and the high potential side switching unit  11 B is off. The switch control signals S 4 A and S 4 B are LOW, switches  13 A and  13 B are set to the predriver unit  5 A and  5 B side, respectively, low potential side switching unit  12 A is OFF, and low potential side switching unit  12 B is ON. The drive current therefore flows from the power supply  6  to the high potential side switching unit  11 A, inductive load  8 , low potential side switching unit  12 B, and to ground  2  through the drive current path.  
      When the phase is changed from this normal (forward) phase drive state, the phase signal S 9  goes from LOW to HIGH and high potential side switching unit  11 A goes off. The state signal S 3  goes HIGH for a predetermined regeneration period starting when the phase signal S 9  changes phase. As a result, the high potential side switching unit  11 B also goes OFF. The characteristics of the inductive load  8  cause regenerative current to continue flowing to the inductive load  8  until the energy stored during the drive period is completely discharged. Switching control signal S 4 A goes LOW, switching control signal S 4 B goes HIGH, switch  13 A is set to the predriver unit  5 A side, and switch  13 B is set to the regenerative gate voltage source  151 B side. The low potential side switching unit  12 A goes to the full ON low resistance ON state, but because the gate voltage S 12 BG of the low potential side switching unit  12 B goes to regenerative gate voltage S 151 B, low potential side switching unit  12 B goes to the half ON high resistance ON state.  
      The regenerative current therefore flows through the regenerative current path from ground  2  to the low potential side switching unit  12 A in a full ON low resistance ON state, the inductive load  8 , the low potential side switching unit  12 B in a half ON high resistance ON state, and to ground  2 . Because no part of the regenerative current path flows to the power supply  6 , the supply-to-ground capacitance  7  can be low. In addition, because the ON resistance of the low potential side switching unit  12 B is high, the voltage at both ends of the inductive load  8  can be set high and the time required for regenerative current attenuation can be shortened.  
      The regeneration period can be set from equation (2) as described in the first embodiment, and the regenerative gate voltage S 151 B can be determined from equation (3).  FIG. 5  shows the change over time in the gate voltage of each switching unit. In the regeneration state the drain voltage S 12 BD of the low potential side switching unit  12 B in the half ON high resistance ON state gradually decreases with regenerative current attenuation.  
      The inductive load drive device then enters the reverse phase drive state after the regeneration period set by the state signal generating unit  3 . The high potential side switching unit  11 B and low potential side switching unit  12 A are thus on, and the drive current flows through the drive current path from the power supply  6  to the high potential side switching unit  11 B, inductive load  8 , low potential side switching unit  12 A, and to ground  2 .  
      The inductive load drive device according to this second embodiment of the invention thus controls the high potential side switching unit group to the off state during the regeneration period so that regenerative current does not flow to the power supply  6 . As a result, the power supply voltage will not rise due current inflow even if an internal resistance  306  is present in the power supply. An extra safety margin is therefore not required when setting the withstand voltage of the inductive load drive device and the size of the supply-to-ground capacitance  7  can therefore be reduced, thus affording a low unit cost. The regeneration period can also be shortened because the regenerative current attenuation time can be shortened, and the time required to switch the phase of the inductive load between forward and reverse can be shortened.  
      More specifically, the resistance of the regenerative current path can be increased by controlling the ON resistance of the low potential side switching unit, the power consumption time is shortened by the path resistance, and the regenerative current attenuation time can be shortened.  
      Phase switching from the forward phase drive state (with current flowing through the drive current path from the power supply  6  to the high potential side switching unit  11 A, inductive load  8 , low potential side switching unit  12 B, and to ground  2 ) to the reverse phase drive state (with current flowing through the drive current path from the power supply  6  to the high potential side switching unit  11 B, inductive load  8 , low potential side switching unit  12 A, and to ground  2 ) is described above. Switching from the reverse phase drive state to the forward phase drive state is controlled in the same way.  
      The high potential side switching units  11 A and  11 B are p-channel MOS transistors in this embodiment of the invention, but the same effect can be achieved using n-channel MOS transistors instead. The switch control unit  4  and predriver units  5 A and  5 B are preferably logic circuits as shown in  FIG. 4 , but other devices that operate as described above can be used instead.  
      The regeneration gate voltage source is split in this embodiment between regenerative gate voltage sources  151 A and  151 B, but a single voltage source can be used because both voltage sources  151 A and  151 B are not used at the same time. Using a single regeneration gate voltage source does not affect the operation and advantage of this embodiment of the invention.  
     Third Embodiment  
       FIG. 6  is a schematic block diagram of an inductive load drive device according to a third embodiment of the invention.  
      This third embodiment replaces the regenerative gate voltage sources  151 A,  151 B used in the second embodiment with differential operators  21 A and  21 B and first reference voltage sources  22 A and  22 B. The differential operators  21 A and  21 B are differential amplifiers, for example. The first reference voltage sources  22 A and  22 B output a predetermined first reference voltage S 22 A and S 22 B, respectively.  
      This embodiment is described below with particular reference to the differences between this embodiment and the second embodiment.  
      In the normal phase drive state, the phase signal S 9  and state signal S 3  are LOW, the high potential side switching unit  11 A is ON, and the high potential side switching unit  11 B is OFF. The switch control signals S 4 A and S 4 B are LOW, the switches  13 A and  13 B are set to the predriver units  5 A and  5 B, respectively, the low potential side switching unit  12 A is off and the low potential side switching unit  12 B is on. As a result, the drive current flows through the drive current path from the power supply  6  to the high potential side switching unit  11 A, inductive load  8 , low potential side switching unit  12 B, and to ground  2 .  
      To switch the drive mode to the reverse phase from the normal phase, phase signal S 9  goes from LOW to HIGH and the high potential side switching unit  11 A goes off. The state signal S 3  goes high for the predetermined regeneration period starting from when the phase signal S 9  changes. The high potential side switching unit  11 B therefore goes off. The characteristics of the inductive load  8  cause regenerative current to continue flowing to the inductive load  8  until the energy stored during the drive period is completely discharged.  
      Switching control signal S 4 A goes LOW, switching control signal S 4 B goes HIGH, switch  13 A is set to the predriver unit  5 A side, and switch  13 B switches to the differential amplifier  21 B side.  
      The second embodiment of the invention shortens the attenuation time by the regenerative gate voltage source  151 B increasing the ON resistance of the low potential side switching unit  12 B. Setting the regenerative gate voltage source  151  is shown in equations (3) and (4) above. This method enables applying the high voltage Vs+Vf (Vmax if Vmax&lt;Vs+Vf) to both ends of the inductive load  8 , but the drain voltage S 12 BD of the low potential side switching unit  12 B thereafter decreases with attenuation of the regenerative current as shown in  FIG. 5 . The attenuation time of the regenerative current at this time can be determined by integrating dt in equation (5), which is a variation of equation (1), across the attenuation range of the regenerative current I(t). Note that Vd(t) is equivalent to the drain voltage S 12 BD of the low potential side switching unit  12 B in the half ON high resistance ON state. 
 
 dt=−L/Vd ( t )× dl ( t )   (5) 
 
      In this third embodiment of the invention the first reference voltage S 22 B is Vs+Vf (Vmax if Vmax&lt;Vs+Vf), and differential amplifier  21 B outputs difference signal S 21 B from drain voltage S 12 BD and first reference voltage S 22 B. This difference signal S 21 B controls the gate voltage S 12 BG of the low potential side switching unit  12 B in the half ON high resistance ON state. As a result, the drain voltage S 12 BD can be held as close as possible to the first reference voltage S 22 B. In this case, the gate voltage S 12 BG of the low potential side switching unit  12 B decreases and the ON resistance Ron of the low potential side switching unit  12 B increases as the regenerative current I(t) attenuates. As a result, the product (I(t)×(Ron)) of the regenerative current I(t) and the ON resistance Ron is substantially constant.  
      Note that drain voltages S 12 AD and S 12 BD are also referred to as the voltage of the first main node.  
       FIG. 7  is a partial circuit diagram describing circuit operation in the regeneration state. Note that the low potential side switching unit  12 A is omitted in the figure because it is in the full ON low resistance ON state. The gate voltage S 12 BG of the low potential side switching unit  12 B is controlled by the differential amplifier  21 B so that the drain voltage S 12 BD of the low potential side switching unit  12 B is always equal to the first reference voltage S 22 B. As a result, a voltage substantially equal to the first reference voltage S 22 B is applied to both ends of the inductive load  8 .  
      The regenerative current therefore flows through the regenerative current path from ground  2  to the low potential side switching unit  12 A in the full ON low resistance ON state, inductive load  8 , the low potential side switching unit  12 B in the half ON high resistance ON state, and to ground  2 . Because no part of the regenerative current path flows to the power supply  6 , the supply-to-ground capacitance  7  can be low. In addition, because the ON resistance of the low potential side switching unit  12 B is high, the voltage at both ends of the inductive load  8  can be set high and the time required for regenerative current attenuation can be shortened.  
       FIG. 8  is a waveform diagram of the voltage at various points. As shown in  FIG. 8  the drain voltage S 12 BD of the low potential side switching unit  12 B is always held equal to the first reference voltage S 22 B. The attenuation time of the regenerative current can be shortened even more than in the second embodiment because Vd(t) in equation (5) is constant at the peak level. The inductive load drive device enters the reverse phase drive state after the regeneration period set by the state signal generating unit  3 . The high potential side switching unit  11 B and low potential side switching unit  12 A are on, and the drive current flows through the drive current path from the power supply  6  to the high potential side switching unit  11 B, inductive load  8 , low potential side switching unit  12 A, and to ground  2 .  
      The inductive load drive device according to this embodiment of the invention turns the high potential side switching unit group off when in the regeneration state, and regenerative current therefore does not flow to the power supply  6 . As a result, the power supply voltage will not rise due current inflow even if an internal resistance  306  is present in the power supply. An extra safety margin is therefore not required when setting the withstand voltage of the inductive load drive device and the size of the supply-to-ground capacitance  7  can therefore be reduced, thus affording a low unit cost. The regeneration period can also be shortened because the regenerative current attenuation time can be shortened, and the time required to switch the phase of the inductive load between forward and reverse can be shortened.  
      Furthermore, because transistor on resistance can be feedback controlled to maximize the drain voltage while not exceeding the withstand voltage of the inductive load drive device, the resistance of the regenerative current path can be maximized more appropriately and the regenerative current attenuation time can be shortened even more because this path resistance shortens the power consumption time.  
      Phase switching from the forward phase drive state (with current flowing through the drive current path from the power supply  6  to the high potential side switching unit  11 A, inductive load  8 , low potential side switching unit  12 B, and to ground  2 ) to the reverse phase drive state (with current flowing through the drive current path from the power supply  6  to the high potential side switching unit  11 B, inductive load  8 , low potential side switching unit  12 A, and to ground  2 ) is described above. Switching from the reverse phase drive state to the forward phase drive state is controlled in the same way.  
      The high potential side switching units  11 A and  11 B are p-channel MOS transistors in this embodiment of the invention, but the same effect can be achieved using n-channel MOS transistors instead. The switch control unit  4  and predriver units  5 A and  5 B are preferably logic circuits as shown in  FIG. 6 , but other devices that operate as described above can be used instead.  
      Two differential operators  21 A and  21 B and first reference voltage sources  22 A and  22 B are used in this embodiment, but a single device can be used for each because neither the differential operators nor the first reference voltage sources are used at the same time. Using a single differential operator and a single first reference voltage source does not affect the operation and advantage of this embodiment of the invention.  
     Fourth Embodiment  
       FIG. 9  is a schematic block diagram of an inductive load drive device according to a fourth embodiment of the invention.  
      In the second embodiment of the invention the regenerative current path passes through the low potential side switching unit group. This fourth embodiment of the invention differs by using the high potential side switching unit group instead of the low potential side switching unit group, and is described below primarily with reference to the differences between this embodiment and the second embodiment.  
      Shown in  FIG. 9  are the inductive load  8 , a drive unit  10  for supplying drive power to the inductive load  8 , predriver units  5 A and  5 B, a power supply  6 , a ground  2 , a capacitance between the power supply and ground  7 , an internal resistance  306  in the power supply, and a phase signal generating unit  9  for generating a phase signal S 9  representing the forward or reverse phase state. A state signal generating unit  3  outputs a state signal S 3  indicating whether the current operating state is the drive state or regeneration state. The state signal S 3  goes HIGH for a predetermined regeneration period starting when the phase signal S 9  changes phase.  
      The drive unit  10  includes high potential side switching units  11 A and  11 B, and low potential side switching units  12 A and  12 B. Each switching unit  11 A,  11 B,  12 A,  12 B has a body diode parallel connected in reverse conductivity. The high potential side switching units  11 A and  11 B have a regeneration switching function similarly to the low potential side switching units  12 A and  12 B in the second embodiment.  
      Switches  13 A and  13 B switch the gate voltage S 11 AG, S 11 BG of the high potential side switching units  11 A and  11 B. The switch control unit  4  generates the switch control signals S 4 A and S 4 B that control the switches  13 A and  13 B, respectively. When the switch control signal S 4 A, S 4 B is LOW, the corresponding switch  13 A and  13 B selects the output from the predriver units  5 A and  5 B, and selects the regenerative gate voltage source  151 A,  151 B when the switch control signal S 4 A and S 4 B is HIGH.  
      The operation of this inductive load drive device during phase switching is described next.  
      In the normal phase (forward) drive state the phase signal S 9  and state signal S 3  are LOW, low potential side switching unit  12 A is OFF and low potential side switching unit  12 B is ON. The switch control signals S 4 A and S 4 B are LOW, switches  13 A and  13 B are set to the predriver unit  5 A and  5 B side, respectively, high potential side switching unit  11 A is ON and high potential side switching unit  11 B is OFF. The drive current therefore flows from the power supply  6  to the high potential side switching unit  11 A, inductive load  8 , low potential side switching unit  12 B, and to ground  2  through the drive current path.  
      When the phase is changed from this normal (forward) phase drive state, the phase signal S 9  goes from LOW to HIGH and low potential side switching unit  12 B goes off. The state signal S 3  goes HIGH for a predetermined regeneration period starting when the phase signal S 9  changes phase. As a result, the low potential side switching unit  12 A also goes OFF. The characteristics of the inductive load  8  cause regenerative current to continue flowing to the inductive load  8  until the energy stored during the drive period is completely discharged. Switching control signal S 4 A goes HIGH, switching control signal S 4 B goes LOW, switch  13 A is set to the regenerative gate voltage source  151 A side, and switch  13 B is set to the predriver unit  5 B side. The high potential side switching unit  11 B goes to the full ON low resistance ON state, but because the gate voltage S 11 AG of the high potential side switching unit  11 A goes to regenerative gate voltage S 151 A, high potential side switching unit  11 A goes to the half ON high resistance ON state.  
      As a result, the regenerative current flows through the regenerative current path from the half ON high resistance ON state high potential side switching unit  11 A to the inductive load  8  and the full ON low resistance ON state high potential side switching unit  11 B. Because no part of the regenerative current path flows to the power supply  6 , the supply-to-ground capacitance  7  can be low. In addition, because the ON resistance of the high potential side switching unit  11 A is high, the voltage at both ends of the inductive load  8  can be set high and the time required for regenerative current attenuation can be shortened.  
      The regeneration period can be set from equation (2) as described in the first embodiment. The regenerative gate voltage S 151 A is determined from equation (3) in the first and second embodiments, but is determined from equation (6) in this embodiment because the regenerative current path goes through the high potential side switching unit group. 
 
( I max)×( R on)&lt; Vs    (6) 
 
 where Vs is the voltage of the power supply  6 , Imax is the maximum current flow to the inductive load  8  in the drive period, and Ron is the ON resistance of the high potential side switching units  11 A and  11 B when in the half ON high resistance ON state. 
 
      The inductive load drive device then enters the reverse phase drive state after the regeneration period set by the state signal generating unit  3 . The high potential side switching unit  11 B and low potential side switching unit  12 A are thus on, and the drive current flows through the drive current path from the power supply  6  to the high potential side switching unit  11 B, inductive load  8 , low potential side switching unit  12 A, and to ground  2 .  
      Phase switching from the forward phase drive state (with current flowing through the drive current path from the power supply  6  to the high potential side switching unit  11 A, inductive load  8 , low potential side switching unit  12 B, and to ground  2 ) to the reverse phase drive state (with current flowing through the drive current path from the power supply  6  to the high potential side switching unit  11 B, inductive load  8 , low potential side switching unit  12 A, and to ground  2 ) is described above. Switching from the reverse phase drive state to the forward phase drive state is controlled in the same way.  
      The high potential side switching units  11 A and  11 B are p-channel MOS transistors in this embodiment of the invention, but the same effect can be achieved using n-channel MOS transistors instead. The switch control unit  4  and predriver units  5 A and  5 B are preferably logic circuits as shown in  FIG. 9 , but other devices that operate as described above can be used instead.  
      The regeneration gate voltage source is split in this embodiment between regenerative gate voltage sources  151 A and  151 B, but a single voltage source can be used because both voltage sources  151 A and  151 B are not used at the same time. Using a single regeneration gate voltage source does not affect the operation and advantage of this embodiment of the invention.  
     Fifth Embodiment  
       FIG. 10  is a schematic block diagram of an inductive load drive device according to a fifth embodiment of the invention.  
      In the third embodiment of the invention the regenerative current path passes through the low potential side switching unit group. This fifth embodiment of the invention differs from the third embodiment by using the high potential side switching unit group instead of the low potential side switching unit group, and is described below primarily with reference to the differences between this embodiment and the third embodiment.  
      In the third embodiment of the invention the first reference voltage S 22 B is Vs+Vf (Vmax if Vmax&lt;Vs+Vf), and the drain voltage S 12 BD is held as high as possible by controlling the gate voltage S 12 BG of the low potential side switching unit  12 B in the half ON high resistance ON state. In this fifth embodiment of the invention the first reference voltage S 22 A is the ground voltage, and the drain voltage S 11 AD is held substantially to the ground potential by controlling the gate voltage S 11 AG of the high potential side switching unit  11 A in the half ON high resistance ON state. In this case the on resistance of the high potential side switching unit  11 A increases as the regenerative current attenuates, and the product (I(t))×(Ron) of the regenerative current I(t) and ON resistance Ron is substantially constant. As a result, the attenuation time can be further decreased as in the third embodiment. The effect of this fifth embodiment is the same as described in the third embodiment, and further description thereof is thus omitted.  
      Phase switching from the forward phase drive state (with current flowing through the drive current path from the power supply  6  to the high potential side switching unit  11 A, inductive load  8 , low potential side switching unit  12 B, and to ground  2 ) to the reverse phase drive state (with current flowing through the drive current path from the power supply  6  to the high potential side switching unit  11 B, inductive load  8 , low potential side switching unit  12 A, and to ground  2 ) is described above. Switching from the reverse phase drive state to the forward phase drive state is controlled in the same way.  
      The high potential side switching units  11 A and  11 B are p-channel MOS transistors in this embodiment of the invention, but the same effect can be achieved using n-channel MOS transistors instead. The switch control unit  4  and predriver units  5 A and  5 B are preferably logic circuits as shown in  FIG. 10 , but other devices that operate as described above can be used instead.  
      Two differential operators  21 A and  21 B and first reference voltage sources  22 A and  22 B are used in this embodiment, but a single device can be used for each because neither the differential operators nor the first reference voltage sources are used at the same time. Using a single differential operator and a single first reference voltage source does not affect the operation and advantage of this embodiment of the invention.  
     Sixth Embodiment  
       FIG. 11  is a schematic block diagram of an inductive load drive device according to a sixth embodiment of the invention.  
      Shown in  FIG. 11  are the inductive load  8 , a drive unit  10  for supplying drive power to the inductive load  8 , predriver unit  5 , a power supply  6 , a ground  2 , a capacitance between the power supply and ground  7 , an internal resistance  306  in the power supply, and a phase signal generating unit  9  for generating a phase signal S 9  representing the forward or reverse phase state. A state signal generating unit  3  outputs a state signal S 3  indicating whether the current operating state is the drive state or regeneration state. The state signal S 3  goes HIGH for a predetermined regeneration period starting when the phase signal S 9  changes phase.  
      The drive unit  10  includes high potential side switching units  11 A and  11 B, low potential side first switching units  31 A and  31 B, and low potential side second switching units  32 A and  32 B. Each switching unit  11 A,  11 B,  12 A,  12 B has a body diode parallel connected in reverse conductivity. The high potential side switching units  11 A and  11 B together render a high potential side switching unit group, and the low potential side first switching units  31 A and  31 B and low potential side second switching units  32 A and  32 B together render a low potential side switching unit group.  
      The high potential side switching units  11 A and  11 B and low potential side first switching units  31 A,  31 B,  32 A, and  32 B each have a body diode parallel connected in reverse conductivity. Switching units  31 A,  31 B,  32 A, and  32 B each have a regeneration switching function similarly to the first embodiment.  
      This sixth embodiment of the invention renders the low potential side switching units  12 A and  12 B in the second embodiment by respectively connecting low potential side first switching units  31 A and  31 B and low potential side second switching units  32 A and  32 B in parallel. The differences between this and the second embodiment are described below.  
      The phase switching operation of this inductive load drive device is described next with reference to  FIG. 11  and the timing chart in  FIG. 12 .  
      In the normal (forward) phase drive state high potential side switching unit  11 A is on and high potential side switching unit  11 B is off, low potential side first switching unit  31 B and low potential side second switching unit  32 B are on, and low potential side first switching unit  31 A and low potential side first switching unit  31 B are off. The drive current therefore flows through a drive current path from the power supply  6  to high potential side switching unit  11 A, inductive load  8 , low potential side first switching unit  31 B, low potential side second switching unit  32 B, and to ground  2 . Because both low potential side first switching unit  31 B and low potential side second switching unit  32 B are on at this time, the inductive load drive device operates in the low resistance ON state.  
      When the phase is switched from this forward phase drive state, the phase signal S 9  goes from LOW to HIGH and high potential side switching unit  11 A turns off. The state signal S 3  goes HIGH for a predetermined regeneration period starting when the phase signal S 9  changes phase. As a result, the high potential side switching unit  11 B also goes OFF. The characteristics of the inductive load  8  cause regenerative current to continue flowing to the inductive load  8  until the energy stored during the drive period is completely discharged. The low potential side first switching unit  31 A and low potential side second switching unit  32 A go on, low potential side first switching unit  31 B goes off, and low potential side second switching unit  32 B goes on. The low potential side first switching unit  31 A is in the low resistance ON state at this time, but the low potential side second switching units  32 A and  32 B are in the high resistance ON state.  
      The regenerative current therefore flows through the regenerative current path from ground  2  to low potential side first switching unit  31 A in the low resistance ON state, low potential side second switching unit  32 A in the high resistance ON state, inductive load  8 , low potential side second switching unit  32 B in the high resistance ON state, and to ground  2 . Because no part of the regenerative current path flows to the power supply  6 , the supply-to-ground capacitance  7  can be low. In addition, because the ON resistance of the low potential side second switching unit  32 B is high, the voltage at both ends of the inductive load  8  can be set high and the time required for regenerative current attenuation can be shortened.  
      As in the first embodiment, the on resistance of the low potential side second switching units  32 A and  32 B can be set using equation (3). The regeneration period can be set using equation (2). The inductive load drive device enters the reverse phase drive state after the regeneration period set by the state signal generating unit  3 . The high potential side switching unit  11 B, low potential side first switching unit  31 A, and low potential side second switching unit  32 A are thus on, and the drive current flows through the drive current path from the power supply  6  to high potential side switching unit  11 B, inductive load  8 , low potential side first switching unit  31 A and low potential side second switching unit  32 A, and to ground  2 .  
      The inductive load drive device according to this sixth embodiment of the invention turns the high potential side switching unit group off in the regeneration period, and the regenerative current therefore does not flow to the power supply  6 . As a result, the power supply voltage will not rise due current inflow even if an internal resistance  306  is present in the power supply. An extra safety margin is therefore not required when setting the withstand voltage of the inductive load drive device and the size of the supply-to-ground capacitance  7  can therefore be reduced, thus affording a low unit cost. The regeneration period can also be shortened because the regenerative current attenuation time can be shortened, and the time required to switch the phase of the inductive load between forward and reverse can be shortened.  
      In addition, the resistance of the regenerative current path can be increased by using a high ON resistance second switching device in the regeneration period, the power consumption time is thus shortened by the path resistance, and the regenerative current attenuation time can be further shortened.  
      Phase switching from the forward phase drive state (with current flowing through the drive current path from the power supply  6  to the high potential side switching unit  11 A, inductive load  8 , low potential side first switching unit  31 B, low potential side second switching unit  32 B, and to ground  2 ) to the reverse phase drive state (with current flowing through the drive current path from the power supply  6  to the high potential side switching unit  11 B, inductive load  8 , low potential side first switching unit  31 A and low potential side second switching unit  32 A, and to ground  2 ) is described above. Switching from the reverse phase drive state to the forward phase drive state is controlled in the same way.  
      The high potential side switching units  11 A and  11 B are p-channel MOS transistors in this embodiment of the invention, but the same effect can be achieved using n-channel MOS transistors instead. The predriver unit  5  is preferably a logic circuit as shown in  FIG. 11 , but other devices that operate as described above can be used instead.  
     Seventh Embodiment  
       FIG. 13  is a schematic block diagram of an inductive load drive device according to a seventh embodiment of the invention.  
      This seventh embodiment of the invention replaces the low potential side switching unit group in the regenerative current path in the sixth embodiment with a high potential side switching unit group, and the arrangement of the drive unit  10  and predriver unit  5  changes accordingly. Other aspects of this embodiment are the same as in the sixth embodiment, the operation and effect of this embodiment are also the same as in the sixth embodiment, and further description thereof is thus omitted below.  
     Eighth Embodiment  
       FIG. 14  is a schematic block diagram of an inductive load drive device according to an eighth embodiment of the invention.  
      Shown in  FIG. 14  are the inductive load  8 , a drive unit  10  for supplying drive power to the inductive load  8 , predriver unit  5 , a power supply  6 , a ground  2 , a capacitance between the power supply and ground  7 , an internal resistance  306  in the power supply, and a phase signal generating unit  9  for generating a phase signal S 9  representing the forward or reverse phase state. A state signal generating unit  3  outputs a state signal S 3  indicating whether the current operating state is the drive state or regeneration state. The state signal S 3  goes HIGH for a predetermined regeneration period starting when the phase signal S 9  changes phase.  
      The drive unit  10  includes high potential side switching units  11 A and  11 B, and low potential side third switching units  131 A,  131 B,  132 A,  132 B. The high potential side switching units  11 A and  11 B together render a high potential side switching unit group, and the low potential side third switching units  131 A,  131 B,  132 A,  132 B are referred to the low potential side switching unit group. Each switching unit  11 A,  11 B, and low potential side third switching units  131 A,  131 B,  132 A,  132 B have a body diode parallel connected in reverse conductivity.  
      As in the first embodiment, the low potential side third switching units  131 A,  131 B,  132 A,  132 B have a regenerative switching function.  
      This embodiment of the invention renders the low potential side switching units  12 A and  12 B in the sixth embodiment by respectively parallel connecting low potential side third switching units  131 A and  131 B having a low ON resistance and low potential side third switching units  132 A and  132 B with a high ON resistance. The low potential side third switching unit group  131 A,  131 B,  132 A,  132 B is rendered by parallel connecting third switching devices, and the number of parallel connected third switching devices in low potential side third switching unit group  132 A and  132 B is less than in the low potential side third switching unit group  131 A and  131 B. The number of parallel connected third switching devices is determines so that when in the full ON state low potential side third switching units  131 A and  131 B are in the low resistance ON state, and low potential side third switching units  132 A and  132 B are in the high resistance ON state.  
      The differences between this eighth embodiment and the sixth embodiment are described below.  
      The phase switching operation of this inductive load drive device is described next.  
      In the normal (forward) phase drive state high potential side switching unit  11 A is on and high potential side switching unit  11 B is off, low potential side third switching units  131 B and  132 B are on, and low potential side third switching units  131 A and  131 B are off. The drive current therefore flows through a drive current path from the power supply  6  to high potential side switching unit  11 A, inductive load  8 , low potential side third switching units  131 B and  132 B, and to ground  2 . Because both low potential side third switching units  131 B and  132 B are on at this time, the inductive load drive device operates in the low resistance ON state.  
      When the phase is switched from this forward phase drive state, the phase signal S 9  goes from LOW to HIGH and high potential side switching unit  11 A turns off. The state signal S 3  goes HIGH for a predetermined regeneration period starting when the phase signal S 9  changes phase. As a result, the high potential side switching unit  11 B also goes OFF. The characteristics of the inductive load  8  cause regenerative current to continue flowing to the inductive load  8  until the energy stored during the drive period is completely discharged. The low potential side third switching units  131 A and  132 A go on, low potential side third switching unit  131 B goes off, and low potential side third switching unit  132 B goes on. The low potential side third switching unit  131 A is in the low resistance ON state at this time, but the low potential side third switching units  132 A and  132 B are in the high resistance ON state.  
      The regenerative current therefore flows through the regenerative current path from ground  2  to low potential side third switching unit  131 A in the low resistance ON state and low potential side third switching unit  132 A in the high resistance ON state, inductive load  8 , low potential side third switching unit  132 B in the high resistance ON state, and to ground  2 . Because no part of the regenerative current path flows to the power supply  6 , the supply-to-ground capacitance  7  can be low. In addition, because the ON resistance of the low potential side third switching unit  132 B is high, the voltage at both ends of the inductive load  8  can be set high and the time required for regenerative current attenuation can be shortened.  
      As in the first embodiment, the on resistance of the low potential side third switching units  132 A and  132 B can be set using equation (3). The regeneration period can be set using equation (2). The inductive load drive device enters the reverse phase drive state after the regeneration period set by the state signal generating unit  3 . The high potential side switching unit  11 B and low potential side third switching units  131 A and  132 A are thus on, and the drive current flows through the drive current path from the power supply  6  to high potential side switching unit  11 B, inductive load  8 , low potential side third switching units  131 A and  132 A, and to ground  2 .  
      The inductive load drive device according to this embodiment of the invention turns the high potential side switching unit group off in the regeneration period, and the regenerative current therefore does not flow to the power supply  6 . As a result, the power supply voltage will not rise due current inflow even if an internal resistance  306  is present in the power supply. An extra safety margin is therefore not required when setting the withstand voltage of the inductive load drive device and the size of the supply-to-ground capacitance  7  can therefore be reduced, thus affording a low unit cost. The regeneration period can also be shortened because the regenerative current attenuation time can be shortened, and the time required to switch the phase of the inductive load between forward and reverse can be shortened.  
      In addition, by rendering the number of switching units that are ON in the regenerative current path, the path resistance can be increased, this path resistance can shorten the power consumption time, and the regenerative current attenuation time can be further shortened.  
      Phase switching from the forward phase drive state (with current flowing through the drive current path from the power supply  6  to the high potential side switching unit  11 A, inductive load  8 , low potential side third switching units  131 B and  132 B, and to ground  2 ) to the reverse phase drive state (with current flowing through the drive current path from the power supply  6  to the high potential side switching unit  11 B, inductive load  8 , low potential side third switching units  131 A and  132 A, and to ground  2 ) is described above. Switching from the reverse phase drive state to the forward phase drive state is controlled in the same way.  
      The high potential side switching units  11 A and  11 B are p-channel MOS transistors in this embodiment of the invention, but the same effect can be achieved using n-channel MOS transistors instead. The predriver unit  5  is preferably a logic circuit as shown in  FIG. 14 , but other devices that operate as described above can be used instead.  
     Ninth Embodiment  
       FIG. 15  is a schematic block diagram of an inductive load drive device according to a ninth embodiment of the invention.  
      This ninth embodiment of the invention replaces the low potential side switching unit group in the regenerative current path in the eighth embodiment with a high potential side switching unit group. Other aspects of this embodiment are the same as in the eighth embodiment, the operation and effect of this embodiment are also the same as in the eighth embodiment, and further description thereof is thus omitted below.  
     Tenth Embodiment  
       FIG. 16  is a schematic block diagram of an inductive load drive device according to a tenth embodiment of the invention.  
      In the second through ninth embodiments described above the state signal generating unit  3  sets the regeneration period by generating a state signal based on a phase signal. This tenth embodiment of the invention, however, sets the regeneration period by detecting regenerative current attenuation based on a comparison of the voltage at both ends of the inductive load  8  and a predetermined second reference voltage. This tenth embodiment of the invention shown in  FIG. 16  differs from the third embodiment shown in  FIG. 6  in that the terminal voltages of the inductive load  8  are input to the state signal generating unit  3 , which generates the state signal S 3  based on these terminal voltages. The differences between this tenth embodiment of the invention and the third embodiment are described below.  
      Referring to  FIG. 16 , the inductive load drive device according to this embodiment of the invention additionally has pull-down resistances  52 A and  52 B for fixing the drain voltages S 12 AD and S 12 Bd of the low potential side switching units  12 A and  12 B at the ground potential, a second reference voltage source  54  for outputting a predetermined second reference voltage S 54 , a switch  55  that operates selectively according to the phase signal S 9 , and a comparator  53  for comparing the output voltage S 55  of the switch  55  with the second reference voltage S 54  to output state signal S 3 . In this embodiment of the invention the state signal S 3  is also called a comparison result signal.  
      In the normal (forward) phase drive state the phase signal S 9  and state signal S 3  are LOW, high potential side switching unit  11 A is ON and high potential side switching unit  11 B is OFF. The switch control signals S 4 A and S 4 B are LOW, the switches  13 A and  13 B are set to the predriver units  5 A and  5 B, respectively, the low potential side switching unit  12 A is off and the low potential side switching unit  12 B is on. As a result, the drive current flows through the drive current path from the power supply  6  to the high potential side switching unit  11 A, inductive load  8 , low potential side switching unit  12 B, and to ground  2 .  
      To switch the drive mode to the reverse phase from the normal phase, phase signal S 9  goes from LOW to HIGH and the high potential side switching unit  11 A goes off. The state signal S 3  goes high for the predetermined regeneration period starting from when the phase signal S 9  changes. The high potential side switching unit  11 B therefore goes off. The characteristics of the inductive load  8  cause regenerative current to continue flowing to the inductive load  8  until the energy stored during the drive period is completely discharged.  
      Switching control signal S 4 A goes LOW, switching control signal S 4 B goes HIGH, switch  13 A is set to the predriver unit  5 A side, and switch  13 B switches to the differential amplifier  21 B side.  
       FIG. 17  is a partial circuit diagram describing circuit operation in the regeneration state. Note that the low potential side switching unit  12 A is omitted in the figure because it is in the full ON low resistance ON state. The gate voltage S 12 BG of the low potential side switching unit  12 B is controlled by the differential amplifier  21 B so that the drain voltage S 12 BD of the low potential side switching unit  12 B is always equal to the first reference voltage S 22 B. As a result, a voltage substantially equal to the first reference voltage S 22 B is applied to both ends of the inductive load  8 .  
      The regenerative current therefore flows through the regenerative current path from ground  2  to the low potential side switching unit  12 A in the full ON low resistance ON state, inductive load  8 , the low potential side switching unit  12 B in the half ON high resistance ON state, and to ground  2 . Because no part of the regenerative current path flows to the power supply  6 , the supply-to-ground capacitance  7  can be low. In addition, because the ON resistance of the low potential side switching unit  12 B is high, the voltage at both ends of the inductive load  8  can be set high and the time required for regenerative current attenuation can be shortened.  
      As the regenerative current attenuates in the regeneration state the gate voltage S 12 BG of the low potential side switching unit  12 B decreases to the first reference voltage S 22 B. When the regenerative current has completely dissipated, the gate voltage S 12 BG is less than or equal to the ON threshold voltage of the low potential side switching unit  12 B, and the low potential side switching unit  12 B turns off. The pull-down resistance  52 B fixes the drain voltage S 12 BD at the ground potential at this time. More specifically, the drain voltage S 12 BD is held equal to the first reference voltage S 22 B during the regeneration period, and is fixed by the pull-down resistance  52 B to the ground potential when the regenerative current has completely dissipated. This switching is detected by the second reference voltage source  54  and comparator  53  to output the state signal S 3 .  FIG. 17  shows only the circuit block related to this detection operation.  
      When this state signal S 3  is applied, the drive unit  10  switches to the reverse phase drive state. The high potential side switching unit  11 B and low potential side switching unit  12 A are ON, and the drive current flows through the drive current path from the power supply  6  to high potential side switching unit  11 B, inductive load  8 , low potential side switching unit  12 A, and to ground  2 .  FIG. 18  is a voltage diagram of the signals at selected points of this operation. Because the reverse phase drive state is enabled as soon as regenerative current attenuation is detected, the operating phase can be switched quickly without wasting time.  
      The inductive load drive device according to this embodiment of the invention turns the high potential side switching unit group off when in the regeneration state, and regenerative current therefore does not flow to the power supply  6 . As a result, the power supply voltage will not rise due current inflow even if an internal resistance  306  is present in the power supply. An extra safety margin is therefore not required when setting the withstand voltage of the inductive load drive device and the size of the supply-to-ground capacitance  7  can therefore be reduced, thus affording a low unit cost. The regeneration period can also be shortened because the regenerative current attenuation time can be shortened, and the time required to switch the phase of the inductive load between forward and reverse can be shortened.  
      The regenerative current attenuation time can be further shortened because attenuation of the regenerative current is monitored and the reverse phase drive state is enabled as soon as dissipation of the regenerative current is detected.  
      The regenerative current does not flow to the power supply side with the inductive load drive device and drive method of the invention, and the power supply voltage is therefore not increased by inflowing current even when there is an internal resistance in the power supply. The withstand voltage of the inductive load drive device can therefore be designed without an extra safety margin, the size of the capacitance between the power supply and ground can therefore be reduced, and the cost can therefore be reduced. The attenuation time of the regenerative current can therefore be shortened, the regeneration period can be minimized, and the forward/reverse phase switching time of the inductive load can be shortened.  
      More specifically, controlling the on resistance of the transistor enables increasing the resistance of the regenerative current path and enables shortening the regenerative current attenuation time because the current consumption time of the path resistance is shortened.  
      Furthermore, because transistor on resistance can be feedback controlled to maximize the drain voltage while not exceeding the withstand voltage of the inductive load drive device, the resistance of the regenerative current path can be maximized more appropriately and the regenerative current attenuation time can be shortened even more because this path resistance shortens the power consumption time.  
      In addition, the resistance of the regenerative current path can be increased by selectively using a high ON resistance transistor in the regeneration state, and the regenerative current attenuation time can be shortened even more because this path resistance shortens the power consumption time.  
      Yet further, by selecting the number of transistors that are on in the regenerative current path, the path resistance can be increased and the regenerative current attenuation time can be further shortened because this path resistance shortens the power consumption time.  
      The regenerative current attenuation time can be yet further shortened by monitoring regenerative current attenuation and switching to the reverse phase drive state as soon as attenuation is completed.  
      Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.  
      Phase switching from the forward phase drive state (with current flowing through the drive current path from the power supply  6  to the high potential side switching unit  11 A, inductive load  8 , low potential side switching unit  12 B, and to ground  2 ) to the reverse phase drive state (with current flowing through the drive current path from the power supply  6  to the high potential side switching unit  11 B, inductive load  8 , low potential side switching unit  12 A, and to ground  2 ) is described above. Switching from the reverse phase drive state to the forward phase drive state is controlled in the same way.  
      The high potential side switching units  11 A and  11 B are p-channel MOS transistors in this embodiment of the invention, but the same effect can be achieved using n-channel MOS transistors instead. The switch control unit  4  and predriver units  5 A and  5 B are preferably logic circuits as shown in  FIG. 16 , but other devices that operate as described above can be used instead.  
      Two differential operators  21 A and  21 B and first reference voltage sources  22 A and  22 B are used in this embodiment, but a single device can be used for each because neither the differential operators nor the first reference voltage sources are used at the same time. Using a single differential operator and a single first reference voltage source does not affect the operation and advantage of this embodiment of the invention.  
      The present invention is described with reference to the foregoing embodiments of the invention by way of example only, and is not limited to these embodiments.  
      The present invention can be used in an inductive load drive device and a drive method for an inductive load drive device.