JP3199722B2 - Bridge type drive circuit and magnetic disk drive using the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bridge-type drive circuit for driving an inductance load and a magnetic disk drive using the same, and in particular, to reduce the size and power consumption of a magnetic head drive circuit. The present invention relates to a bridge type driving circuit suitable for the above and a magnetic disk device using the same.

[Conventional technology]

As a general method of low power consumption driving when supplying current to an inductance load, there is a PWM driving method, and as a well-known example of this, Naoki Mishiro, “Servo power electronics of microcomputer edge”, Sogo Denshi Shuppan (1989)
Year) on pages 135-141. FIG. 12 is a circuit diagram for explaining a conventional PWM driving method, and corresponds to, for example, FIG. Such a circuit is called an H-bridge circuit because of its shape. Tr ₁ and T
r ₃ is the upper arm transistor of the H-bridge type drive circuit, Tr
₂ and Tr ₄ are called lower arm transistors. here,
From Tr ₁ which is an example in which the four Tr ₄ in NPN transistor. _D01 to _D04 are diodes, and M is an inductance load of a motor or the like. As the load current I _L in the driving circuit, when supplying positive current direction of the arrow in the figure, clear Tr ₂ and Tr _3, and Tr ₄ are turned on, the Tr ₂ on-off drives (PWM driving)
I do. Then, when Tr ₁ is turned on, Tr ₁ ⇒ M from the power supply V _DDH
⇒ When current increases while Tr ₄ flows, and Tr ₁ is off
D ₀₂ ⇒M⇒Tr ₄ and the return current (or regenerative current) flow while decreasing. That is, it is possible to control the current average value of the load current I _L by Tr ₁ controls the duty ratio of on. Tr ₁ and T to control negative load current I _L
r ₄ may be turned off, Tr ₂ may be turned on, and Tr ₃ may be turned on / off (PWM drive).

On the other hand, a method in which Tr ₁ and Tr ₃ of the upper arm transistor are continuously turned on without performing on / off driving (PWM driving), and the current is continuously supplied for driving is referred to as linear driving. In the case of linear driving, the main operating region of each transistor is in a linear region in which both the emitter-collector voltage and the collector current are not near zero. Therefore, power consumption corresponding to the product of the emitter-collector voltage of the transistor and the collector current is large. In the PWM drive, each transistor is used in a saturated state (on state) in which a small voltage is not applied between the emitter and the collector, or in a cutoff state (off state) in which the collector current does not flow, so that the power consumption is small. Therefore, there is a problem in that the linear drive consumes more power in the transistor than the PWM drive.

Now, in the magnetic disk drive, the voice coil motor for moving the magnetic head is driven. There is a demand that this voice coil motor forms an inductance load and that it be driven with as low power consumption as possible.
In the control of the magnetic head, there is a seek period in which the magnetic head is first moved to the position of the target track at high speed. Next, there is a following period in which a torque is generated in proportion to the repulsive force of a spring pressing the magnetic head after moving to the target track, and the magnetic head is fixed on the target track and follows this. During the seek period, a large current is supplied to the voice coil motor to move the magnetic head at high speed. In a typical example of a 3.5-inch magnetic disk, a current of about 1 A is supplied. During the following period, a small current is supplied because it is only necessary to follow the target track. A similar typical example supplies about 100 mA. Reading of data stored on the disk is mainly performed during the following period. During the seek period, servo data such as the current track position required for the magnetic head to reach the target track is read.

One of the characteristics of the drive of the magnetic disk device is that the drive of a large current (seek period) and the drive of a small current (following period) are performed in a mixed manner.

[Problems to be solved by the invention]

Load current I _L in the case of the conventional PWM driving becomes sawtooth wave including a high frequency current component. At this time, the average load current is set using the first active element having a large current driving capability even during the following period in which the load current is small. For this reason,
There is a drawback that the peak value of the pulse-like load current increases and radiated noise increases. This is taken into the magnetic head. For this reason, there is a problem that the above-mentioned data and the above-mentioned servomotor cannot be read normally by the magnetic head.

Further, since the peak value of the load current is large, the duty ratio of the PWM drive needs to be sufficiently reduced accordingly. For this reason, there is a disadvantage that the controllability for keeping the average load current constant during the following period is poor.

Therefore, conventionally, it has been necessary to use a linear drive with low noise for driving the voice coil motor. Therefore, there is a problem that the power consumed by the driving transistor cannot be reduced.

Amount of power consumption in a linear drive, in the above example, the track-following period the load current I _L the resistance of the voice coil motor is as small as about 10Ω, which is the load to 100mA and small. For this reason, only about 1 V is consumed by the voice coil motor. Therefore, most of the power supply voltage is applied to the active element, and it has not been possible to sufficiently reduce power consumption during the following period. As a result, the drive circuit of the above example required power consumption of 1 W or more.

Here, there is a demand to integrate the above-described drive circuit and servo circuit on one integrated circuit (one chip). However, in general, if the power consumption of the integrated circuit is not suppressed to 1 W or less, a device such as forced cooling is required, and there is a problem that it cannot be applied to ordinary small devices. Therefore, in the drive circuit using the linear drive, there is a problem that it is difficult to integrate the circuit into one chip.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a bridge-type drive circuit using low-power-consumption, low-noise PWM drive and a magnetic disk device using the same. .

[Means for solving the problem]

Means of the present invention for achieving the above object include a first active element (M _UL ) connected in series between a first operating potential point (V _DDH ) and a second operating potential point (GND). , A second active element (M _DL ), and a third active element (M _UR ) connected in series between the first operating potential point (V _DDH ) and the second operating potential point (GND). ), A fourth active element (M _DR ), the first active element (M _UL ), and the second active element (M _DR ).
_DL ), a first terminal connected to a common connection point with the third active element (M _UR ), and a fourth terminal (M _UR ).
_DR ), a second terminal connected to a common connection point with the first terminal and the second terminal, and by connecting a load (L _VCM ) between the first terminal and the second terminal, the first period At
By conducting the first active element (M _UL ) and the fourth active element (M _DR ), the first operating potential point (V _DDH ) and the second operating potential point (GND) can be set. A bridge-type drive circuit configured to flow a current through a path of the first active element (M _UL ), the load (L _VCM ), and the fourth active element (M _DR ) , the first active element (M _UL) from the first operating potential point in parallel (V _DDH) and the said first active element between a first terminal (M _UL) from essentially zero current 5th with small supply capacity
In the second period, the first active element (M _UL ) is non-conductive, the fourth active element (M _DR ) and the fifth active element (M _ULX ) are connected in the second period. _ULX ), the fifth active element (M _ULX ) and the load (L _VCM ) are connected between the first operating potential point (V _DDH ) and the second operating potential point (GND). )
And a bridge-type drive circuit characterized in that a current flows through the path of the fourth active element ( _MDR ), and a magnetic disk device using the same. (See FIG. 1).

[Action]

In the first period, a large current can be supplied to the load by the first active element having a large current supply capability. Therefore, for example, in a magnetic disk drive, the seek period until the magnetic head moves to the position of the target track can be shortened.

In the second period, a small current is supplied to the load by the fifth active element having a small current supply capability. Therefore, for example, in the second period of the magnetic disk device, that is, in the following period in which the magnetic head is fixed on the target track by supplying a small current to the load, the fifth active element having a small current supply capability loads the magnetic head. Can be driven.

Therefore, the peak value of the load current can be reduced, and the PW
The duty ratio of M drive can be increased. As a result, controllability for keeping the average load current constant during the following period can be improved. In addition, this method has an effect that the radiated noise can be significantly reduced because the peak value of the load current is small. This has the effect that a low power consumption PWM drive circuit can be used in the voice coil drive circuit of the magnetic disk drive. In addition, the reduction in power consumption has an effect that the drive circuit can be easily integrated.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a drive circuit diagram of a first embodiment of the present invention. V
_DDH is the power supply voltage of the output circuit, L _VCM is the inductance of the voice coil motor, R _VCM is the resistance component existing in series with the L _VCM, and is the sum of the parasitic resistance component of the voice coil motor and the sense resistor for load current detection, I _VCM Is the load (L _VCM and R _VCM )
Is the load current flowing through The control of the magnetic head consists of a seek period during which the magnetic head is moved to the target track and a following period during which the magnetic head is moved to the target track, generating a torque that balances the repulsive force of the spring pressing the magnetic head, and fixing the magnetic head to the target track. Consists of M _UL , M _UR , M
_DR and M _DL are N-channel MOS transistors for supplying current to L _VCM during a seek period, and M _ULX and M _URX are N-channel MOS transistors for supplying current to L _VCM during a following period. D ₀₄ from the diode D ₀₁ for circulating current that was in FIG. 12 of the prior art is to substitute the drain-body diode of the MOS transistor in this case. In the present embodiment, instead of the linear drive system used in the voice coil motor drive circuit of the conventional magnetic disk drive to reduce the power consumption of the transistor, the PW
M drive was used. In order to prevent noise, which is a disadvantage of PWM, MOS transistors M _ULX and M _URX for following are provided about one digit smaller than MOS transistors M _UL and M _UR used for seeking. M _ULX (M _URX ) is a MOS transistor M _UL (M
_{Since the} current drive capability is about one digit smaller than that of ( _UR ), the maximum value of the load current is smaller than that of the case where the PWM drive at the time of following is performed by _MUL ( _MUR ). For this reason, it is possible to reduce the magnitude of the radiated noise that enters the magnetic head by the PWM drive. Also, the desired average load current I _VCM (
_mean ), the on-duty of PWM drive is M _ULX (M
_{Using URX} ) has the advantage that the pulsating current of the I _VCM is small and that accurate current control can be performed. In addition, since M _ULX (M _URX ) has a smaller input capacity than M _UL (M _UR ), there is an advantage that the gate drive power of the MOS transistor can be reduced.

PWM driving during the following period can be performed by the following method. To obtain a positive I _VCM , drive _MULX by PWM. That is, the M _ULX and M _DR in the ON state, M _UL and M _UR and M
Turn off _DL and M _URX , supply current to the load through the path of M _ULX ⇒ L _VCM , R _VCM ⇒ M _DR , and when the load exceeds the target load current, turn off M _ULX and turn M _DL ⇒ L _VCM, switch to return current modes R _VCM ⇒M _DR. When the load current has reached the target value or less, the _MULX is turned on again. Here, even if M _DL is turned off when M _ULX is turned off, the load current can be supplied because the drain-body of M _DL is forward-biased, but the decay time constant of the load current is reduced. when you turn off M _ULX it is also possible to reduce the voltage drop across the M _DL turn on the M _{DL. MURX} is PWM driven to supply reverse following load current.
Since the purpose of current driving at the time of following is to generate a torque in the opposite direction balanced with the spring pressing the magnetic head, the direction of the load current to be supplied may be only one direction. In this case, the MOS transistor _MURX for following becomes unnecessary. In the case of a magnetic disk device, two drive elements are provided in parallel because there are two types of current levels to be supplied to the load.
Further drive elements can be added in parallel with the _UL and _MUR .

FIG. 2 is a time chart in the case of performing a PWM drive during a seek period in the first embodiment of the present invention. Since the current level is originally large during the seek period, the power supply voltage is generally almost applied to the load even in the case of the linear drive, and the loss of power consumption is small. For this reason, the effect of reducing the power consumption of the transistor even when PWM driving is performed is small. However, when an N-channel MOS transistor is used as the upper arm transistor, it is necessary to boost the gate with a powerful charge pump circuit in order to increase the follow-up speed for obtaining the target current in the linear drive. There is a problem that it is necessary to prevent the noise caused by the clock from affecting the reading of the servo data. On the other hand, the PWM drive has an advantage that the boosting of the gate can be easily performed by using the bootstrap method.

Since the average current of the I _VCM during the seek period is as high as 1 A or more in this embodiment, it is difficult to reduce the noise due to the on / off operation. In the case of the analog servo system using the linear drive, since the above-mentioned noise does not occur, the servo data is always read during the seek period. However, when the voice coil motor is driven by PWM, large radiated noise enters the magnetic head during the seek period, and it becomes difficult to read the normal servo data. For this reason, the present embodiment provides a new data reading method that combines the features of the sector servo method of intermittently reading servo data with the features of PWM drive that performs on / off operations intermittently. In the sector servo method, a track signal is written at a predetermined position on a magnetic disk, and the information is read every servo cycle to perform digital servo. For this reason, by performing the timing of the current switch in the PWM drive at a time different from the timing of reading the servo data, even if there is high radiated noise generated from the voice coil motor, the reading of the servo data is not affected. Do not give.
Therefore, there is an advantage that a normal seek can be performed. Taking the case where the servo cycle is 200 μs and the PWM cycle is 50 μs as an example, the following is specifically described. Set the first 25μs of the servo cycle to the servo data reading period,
The first 25 μs of the PWM cycle is set to a period in which the load current is not supplied from the power supply (a period in which only the return current mode occurs).
If the latter 25 μs of the PWM cycle is set to a period during which the load current can be supplied from the power supply, that is, a period during which switching of the active element may occur, switching of the active element will never occur during the period of reading servo data. Not done. Therefore, noise due to switching of the active element does not adversely affect the reading of servo data. It is desirable that the PWM frequency be higher than the servo frequency to prevent resonance with the mechanical system due to the PWM drive.

The PWM drive during the seek period will be described below with reference to FIG. To obtain a positive I _VCM may be PWM driven M _UL. That is, the M _UL and M _DR in the ON state, M _ULX and M _UR
, M _DL and M _URX are turned off, the current is supplied to the load through the path of M _UL ⇒ L _VCM ⇒ M _DR , and when the load current exceeds the target load current, M _UL is turned off and M _DL ⇒ L supplying a switching load current return current mode of _VCM ⇒M _DR. When the load current has reached the target value or less, the _MUL is turned on again. Here, the voltage at the drain-body diode between the can supply M _DL load current for the drain-body M _DL even if you leave off the M _DL is forward biased when off the M _UL Since the voltage drop when the _MDL is turned on can be smaller than the voltage drop, it is desirable to drive the _MUL and the _MDL in opposite phases by PWM to reduce power consumption. At this time, if _MUL and _MDL are turned on at the same time,
Care must be taken for the timing of through current flowing from _VDDH . To supply a load current in the opposite direction, _MUR is driven by PWM. Here, MOS transistor M _ULX for following
The gate voltage does not need to be raised to _VDDH or higher because the ON resistance of the _MURX does not need to be small. However, when N-channel MOS transistors are used as the seek MOS transistors M _UL and M _UR , the on-resistance is reduced when the gate voltage is boosted and driven compared to the power supply voltage V _DDH by a method such as bootstrap or charge pump. There is an effect.

The concept of performing the current switch timing at a different time from the servo data reading timing is especially
It is important in driving, but even in the case of driving with a normal linear amplifier, the drive current that does not change the supply current to the load at the servo motor reading timing, or even if it changes it, it is not possible to perform the drive that does not make a sudden change during the seek time Desirable as a low noise servo method.

FIG. 3 is a detailed drive circuit diagram of the first embodiment of the present invention.
FIG. 4 is the driving table. FIG. 3 shows only the left arm drive circuit. The load at the right end _LVCM is provided, and a circuit similar to that shown in the figure is provided symmetrically on the right side of the load (in the present embodiment, a negative-direction following circuit is not provided). R ₁ , R ₂ , R ₄
Is a gate resistance for reducing the change rate of the drain current of the MOS transistor. A _L is a voltage terminal for turning on / off the M _DL , and B _L is a voltage terminal for turning on the M _UL . C _L is a clock input terminal for the charge pump circuit for boosting the gate of M _UL to the power supply voltage V _DDH or higher, and D _L is M _ULX
This is a voltage terminal for turning on and off. C ₁ is the bootstrap capacitor for boosting the gate of M _UL over the power supply voltage V _DDH. You may only use one either has a combination of a charge pump circuit and the bootstrap circuit for the gate boosting of M _UL in this circuit.

FIG. 5 is a block circuit diagram of the first embodiment of the present invention. VCM is a voice coil motor. Conventional magnetic disk drives perform digital calculations based on target track data and servo information detected by the current magnetic head, determine the target speed, convert it to an analog signal, and, if necessary, prevent mechanical vibration. The signal after passing through a notch filter is input to a linear amplifier for driving. On the other hand, the voice coil motor drive circuit of the present invention can convert a digital signal into a signal pulse width as it is and drive the same, so that the calculation result of the digital operation circuit is not converted to an analog signal and the PWM voice coil drive circuit is not used. Therefore, there is an advantage that the number of parts can be reduced. Further, according to the present invention, the power consumption of the VCM driver circuit can be reduced, so that a digital arithmetic circuit including a microprocessor or a digital signal processor used for servo can be integrated with the driver circuit on one chip. Therefore, there is an effect that the drive board can be downsized.

FIG. 6 shows a fifth embodiment of the PWM drive circuit according to the first embodiment of the present invention.
This is an interface circuit in the case where a digital signal is not directly input as shown in the block diagram of FIG. V _IN is the control input voltage corresponding to the target current value flowing through the voice coil motor, V _ref0 is the current value actually flowing through the voice coil motor or a reference voltage obtained by superimposing a sawtooth wave on the position signal waveform where the magnetic head exists. It is. The magnitude relationship between V _IN and V _ref0 is compared by the comparator 3, and based on the result, the current flowing to the load is pulse width modulated. V _ref1 is a reference voltage for the comparator 1 to determine whether the load current in the positive direction is set to the seek mode or the following mode, and V _ref2 is set to the following mode for the positive current or the seek of the negative current. This is a reference voltage for the comparator 2 to determine whether to set the mode. The voltage obtained by the pulse width modulation is applied to the input terminals A _L , B _L , C _L , D _L , A _R , B _R , and C _R in FIG. 3 in a control mode. A signal which becomes "L" during the read period of the servomotor is applied to the input Z in FIG. This allows the second
As described in the figure, it is possible to prevent a sudden change in load current at the time of seeking.

FIG. 7 is a block circuit diagram for further reducing the noise of the driving circuit according to the first embodiment of the present invention. In this embodiment, a high-pass filter is provided in parallel with the _LVCM in order to reduce the high-frequency component flowing through the _LVCM of the load, so that a high-frequency current component that causes radiated noise jumping into the magnetic head does not flow into the load.

FIG. 8 shows a driving circuit according to a second embodiment of the present invention. In this embodiment, the N-channel MOS transistors M _ULX and M _URX for following shown in FIG.
It is substantially the same as the first embodiment, _except that it is configured with M _ULY and M _URY . Here, the current driving capability of the M _ULy and M _URY is that each be designed small compared to M _UL and M _UR is the same as the first embodiment.

FIG. 9 shows a driving circuit according to a third embodiment of the present invention. In this embodiment, the M _ULX the first embodiment in that M _UL1 and M _UL2 2
Composed of elements, there is shown an embodiment in which the M _URX was composed of two elements that M _UR1 and M _UR2. M _UL1 and M _UL2 (M _UR1
By shifting the ON / OFF timing of M _UR2 ), the current flowing to the load can be _smoothed, and the high-frequency current component can be made difficult to flow, and noise can be reduced. In this embodiment, the case where the transistor for following is divided into two is shown, but it is also possible to further divide the transistor into three and shift the ON / OFF timing. Similarly, if the gates of the seek MOS transistors M _UL and M _UR are divided into two or more parts and the individual transistors are driven with a delay, noise during seek can be reduced.

FIG. 10 is a detailed drive circuit diagram of the third embodiment of the present invention. Although only the left arm drive circuit is shown as in FIG. 3 of the present invention, a similar circuit is provided for the right arm. R ₁ , R ₂ , R ₄ and R ₅ are gate resistors for reducing the rate of change of the drain current of the MOS transistor. Becomes possible to reduce a high frequency component of the PWM current in the track-following change the switching speed of the M _UL1 and M _UL2 by varying the resistance of R ₄ and R _5. A _L , B _L , C _L , D _{L and the} like play the same role as in FIG.

FIG. 11 shows a fourth embodiment of the present invention. In this embodiment, a case is shown in which the upper arm MOS transistors M _UL and M _UR for seeking are configured by P-channel MOS transistors. Here, the upper arm MOS transistor M for following
The current driving capability of _ULY and M _URY are each that is designed smaller than in the M _UL and M _UR is the same as the first embodiment and the like. In the case of the present embodiment, it is not necessary to boost the gate voltage to a level higher than the power supply voltage, so that there is an advantage that the following regenerative current driving effective for reducing power consumption can be easily performed. That is,
To obtain a positive I _VCM in the seek period may be PWM driven M _UL. That is, _MUL and _MDR are turned on, and _MUL and _MDR are turned on.
Turn off _ULX , M _URX , M _UR, and M _DL , and set M _UL ⇒L _VCM ⇒M _DR
The current is supplied to the load through the path, and when the load reaches or exceeds the target load current, _MUL and _MDR are turned off, and then _MUR
And turns on the M _DL, switched to the regenerative current mode that M _DL ⇒L _VCM ⇒M _UR. When the load current has reached the target value or less, _MUR and _MDL are turned off again, and _MUL and _MDR are turned on. Here, power consumption can be reduced because the energy stored in L _VCM is returned to the power source by the regenerative current mode. Here, the purpose of turning on M _UR and M _DL in the regenerative mode is to reduce the power consumption of these elements, and the current flows through the diode between the drain and source of M _UR and M _DL even when it is off. It is possible to shed.

〔The invention's effect〕

According to the present invention, the PWM drive can be introduced into the voice coil motor drive of the magnetic disk device that requires low noise drive, so that there is an effect that low power consumption drive becomes possible. In addition, this makes it possible to integrate the servo circuit and the drive circuit into one chip, which has the effect of reducing the size of the drive circuit.

[Brief description of the drawings]

FIG. 1 is a drive circuit diagram of a first embodiment of the present invention, and FIG. 2 is a drive circuit diagram of a first embodiment of the present invention.
FIG. 3 is a detailed drive circuit diagram of the first embodiment of the present invention, FIG. 4 is a drive table thereof, and FIG. 5 is a first embodiment of the present invention. FIG. 6 is a block circuit diagram of the embodiment, FIG. 6 is a logic circuit diagram for an interface when an input of the output circuit of the first embodiment of the present invention is an analog signal, and FIG. 7 is a diagram of the first embodiment of the present invention. FIG. 8 is a block circuit diagram for further reducing noise of the driving circuit, FIG. 8 is a driving circuit diagram of the second embodiment of the present invention, and FIG.
FIG. 10 is a drive circuit diagram of a third embodiment of the present invention, FIG. 10 is a detailed drive circuit diagram of a third embodiment of the present invention, FIG. 11 is a drive circuit diagram of a fourth embodiment of the present invention, FIG. 12 is a diagram of a conventional PWM drive circuit. M _UR , M _UL ... N-channel MOS transistor or P-channel MOS transistor, M _DR , M _DL , M _URX , M _ULX , M _UL1 , M _UL2 , M
_{UR1, M UR2, M 1 ~M} 4, M 7, M 8 ...... N -channel MOS _{transistor, M URY, M ULY, M} 5, M 6 ...... P -channel MOS transistor,
Tr _{1 to} Tr ₄ …… NPN transistors, D _{1 to} D ₁₁ , D _{01 to} D ₀₄ ……
Diode, R _{1 to} R ₅ … Resistance, R _VCM …… Resistance (including parasitic resistance) in series with the voice coil motor, L _VCM …… Voice coil motor inductor, A _L , B _L , C _L , D _L , A _R , B _R , C _R ……
Input terminal of output circuit, Z: Input terminal that goes to “L” state during servo data reading period, _VIN: Input voltage, V _DDH
…… Power supply voltage, V _ref0 , V _ref1 , V _ref2 …… Reference voltage, VCM…
… Voice coil motors, 1 to 3 …… comparators, 4 to
6 Transfer gate, 7-14 Inverter
15-24… AND circuit, 25,26… OR circuit, 27-30 …… Delay circuit.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Isao Yoshida, Inventor 1-280, Higashi Koikekubo, Kokubunji City, Tokyo Inside the Central Research Laboratory of Hitachi, Ltd. Central Research Laboratory (56) References JP-A-50-52528 (JP, A) JP-A-55-35893 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02K 5/00 , 5/05 H02K 5/28-5/44 H02K 6/00-6/24 H02K 7 / 00,7 / 05 H02K 7/36-7/66 H02M 7/42-7/98

Claims (17)

(57) [Claims] A first active element and a second active element connected in series between a first operating potential point and a second operating potential point; the first operating potential point and the second active potential point; A third active element and a fourth active element connected in series between the first active element and the second active element, and a first active element connected to a common connection point between the first active element and the second active element. And a second terminal connected to a common connection point between the third active element and the fourth active element. A load is placed between the first terminal and the second terminal. Is connected between the first operating potential point and the second operating potential point by conducting the first active element and the fourth active element in the first period. A bridge-type drive configured to flow a current through a path of the first active element, the load, and the fourth active element A fifth active circuit having a current supply capability substantially smaller than that of the first active element between the first operating potential point and the first terminal in parallel with the first active element. Connecting the first active element to the non-conductive state, and setting the fourth active element and the fifth active element to conductive during the second period, thereby connecting the first operating potential point to the first operating potential point. A bridge-type drive circuit, wherein a current is caused to flow between the second active potential point and the second active potential point via a path of the fifth active element, the load, and the fourth active element. 2. The method according to claim 1, wherein a current flows through the load during the second period by a PWM driving method in which conduction of the fifth active element is performed intermittently. A bridge-type drive circuit as described. 3. The method according to claim 1, wherein the second active element comprises a MOS transistor, and when the fifth active element is intermittently conducted in the PWM driving method, the fifth active element is turned off. Current is configured to flow through a path of the MOS transistor, the load, and the fourth active element.
3. The bridge-type drive circuit according to claim 2, wherein the bridge-type drive circuit is constituted by an on-current generated by turning on a transistor or a current flowing through a diode between a body and a drain of the MOS transistor. 4. The PWM driving method is controlled such that the average duty ratio when the fifth active element is turned on when the fifth active element is turned on intermittently is 1/2 or less. 3. The bridge-type drive circuit according to claim 2, wherein: 5. The semiconductor device according to claim 1, wherein said first and third active elements are N-channel MOS transistors, and said first and third N-channel MOS transistors are connected to a gate of said first transistor when said first or third N-channel MOS transistor is conductive. 2. The bridge-type drive circuit according to claim 1, wherein a voltage higher than the voltage at the operating potential point is applied. 6. The bridge-type driving circuit according to claim 5, wherein said fifth active element is an N-channel MOS transistor. 7. The bridge-type drive circuit according to claim 1, wherein said first and third active elements comprise P-channel MOS transistors. 8. The bridge-type drive circuit according to claim 7, wherein said fifth active element is a P-channel MOS transistor. 9. At least one of the first to fourth active elements is formed of a MOS transistor, the gates of which are separated from each other, and the pull-down capability or the pull-up capability varies with time. 2. The bridge-type drive circuit according to claim 1, wherein the bridge-type drive circuit is a composite element formed so as to be capable of reducing a time variation rate of rise or fall of a current. 10. The bridge-type drive circuit according to claim 1, wherein the control data for said bridge-type drive circuit comprises digital data. 11. The bridge-type drive circuit according to claim 1, wherein a filter circuit is connected in parallel with said load to prevent a current having a high frequency component from flowing through said load. 12. The bridge-type drive circuit according to claim 11, wherein said bridge-type drive circuit is formed coexisting on the same integrated circuit chip as said filter circuit. 13. The bridge-type drive circuit is formed so as to coexist on the same integrated circuit chip as a microprocessor or a digital signal processor for driving the filter circuit and the bridge-type drive circuit. 12. The bridge-type drive circuit according to claim 11, wherein: 14. A magnetic disk drive using the bridge type drive circuit according to claim 1 and driving a voice coil motor as the load. 15. A method as set forth in claim 1, wherein the reading of the information on the magnetic disk is performed at a time which does not coincide with the switching time of each of the first to fourth active elements in the first period. 15. The magnetic disk drive according to claim 14, wherein: 16. A magnetic disk drive according to claim 14, wherein a switching frequency of at least one of said first to fourth active elements is higher than a servo frequency for controlling a magnetic head. . 17. The magnetic disk drive according to claim 14, wherein a high-pass filter for preventing noise is provided in parallel with said voice coil motor.