Motor drive device, method, and cooling device using the same

The present invention relates to a motor drive device using a Hall element.

As a method of driving a single-phase motor, a Hall element is used to detect the position of the rotor, and a voltage is applied to the coil of the single-phase motor according to the position information of the rotor to control the coil current to rotate the rotor. A method of controlling is known (Patent Document 1).

Conventionally, as described in FIG. 1 of Patent Document 1, a transistor that inputs an output signal of a Hall element to a hysteresis comparator, converts it into a square wave signal, and constitutes an H-bridge circuit based on this square wave signal. By turning on and off, the coil of the motor is energized to control the rotation. At this time, by delaying the square wave signal output from the hysteresis comparator, at the timing of phase switching, of the transistors constituting the H-bridge circuit, both of the two transistors connected in series between the power supply and the ground are connected. Set a period of off (hereinafter referred to as dead time). As a result, when the phase is switched, the through current is prevented from flowing through the transistors constituting the H-bridge circuit.<patcit num="1"><text>Japanese Unexamined Patent Publication No. 7-87775</text></patcit>

<p> When the motor is driven with a dead time in between as in the technique described in Patent Document 1, the regenerative current is generated during the dead time period via a freewheel diode provided in parallel with the transistor constituting the H bridge circuit. It will flow.</p><p> However, in the technique described in Patent Document 1, the time waveform of the regenerative current flowing through the freewheel diode may change suddenly or have a large peak. As a result, there is a possibility that a large noise is generated or a large voltage is applied to the transistors constituting the output circuit such as the H-bridge circuit due to the counter electromotive voltage.</p><p> The present invention has been made in view of the above problems, and an object of the present invention is to provide a motor drive device capable of gradually changing the coil current when the phase of the motor is switched.</p>

<p> The motor drive device of an aspect of the present invention includes a Hall element that outputs first and second sine wave signals that are opposite to each other depending on the position of the rotor, and a first sine wave signal that is output from the Hall element. A hysteresis comparator that compares with the second sine wave signal and outputs a square wave signal, and detects the timing of phase switching based on the first and second sine wave signals output from the Hall element, and the phase is cut. A drive that drives a motor to be driven by synthesizing a pulse width modulation signal generation circuit that outputs a pulse width modulation signal whose duty ratio gradually changes for a predetermined period of time, and a square wave signal and a pulse width modulation signal by logical calculation. It is equipped with a circuit.</p><p> According to this aspect, at the timing of phase switching, the energization period is controlled based on the pulse width modulation signal in which the duty ratio gradually changes, so that the coil current can be changed gently.</p><p> The pulse width modulation signal generation circuit compares the amplifier that amplifies the difference between the first and second sine wave signals output from the Hall element and outputs it as an absolute value signal, and the absolute value signal output from the amplifier with the periodic voltage. It may include a pulse width modulation comparator that outputs a pulse width modulation signal. In this case, the absolute value signal becomes a periodic signal that becomes the minimum value at the timing of phase switching (hereinafter, also referred to as zero cross). By comparing this absolute value signal with a triangular wave or sawtooth periodic voltage, the pulse width modulation comparator can generate a pulse width modulation signal in which the duty ratio gradually changes during the phase switching period.</p><p> The amplifier may be configured with its gain adjustable by an external resistor. By changing the gain of the amplifier, the length of the predetermined period of phase switching can be adjusted.</p><p> The drive circuit may include an H-bridge circuit as an output stage. This drive circuit may drive the low-side switch based on the square wave signal and may drive the high-side switch based on the pulse width modulation signal.</p><p> The above-mentioned motor drive circuit includes a temperature detection circuit that generates a temperature-dependent temperature detection voltage, and a comparator that generates a temperature pulse width modulation signal in which the duty ratio changes based on the comparison result between the temperature detection voltage and the periodic voltage. , And the drive circuit may synthesize the temperature pulse width modulation signal and the pulse width modulation signal and the square wave signal by logical calculation. In this case, the control of the motor reflecting the temperature can be realized.</p><p> The above-mentioned motor drive circuit smoothes a pulse width-modulated control signal that controls the rotation speed of the motor to be driven and outputs it as a rotation control voltage, and is based on a comparison result between the rotation control voltage and the periodic voltage. A comparator that generates a rotation control pulse width modulation signal whose duty ratio changes is further provided, and the drive circuit logically calculates and synthesizes the rotation control pulse width modulation signal, the pulse width modulation signal, and the square wave signal. May be good.</p><p> In the smoothing circuit, a control signal is input to the base, a transistor grounded at the emitter, a capacitor connected between the collector and ground of the transistor, one end is connected to the collector of the transistor, and a predetermined voltage is applied to the other end. The signal appearing in the collector of the transistor may be output as the rotation control voltage. In this case, the control signal input from the outside can be reflected in the control of the motor.</p><p> The above-mentioned motor drive device may be integrally integrated on one semiconductor substrate. The term "integrated integration" includes the case where all the components of the circuit are formed on the semiconductor substrate and the cases where the main components of the circuit are integrally integrated, and is used for adjusting the circuit constant. A resistor or a capacitor may be provided outside the semiconductor substrate. The circuit area can be reduced by integrating the motor drive device as one LSI.</p><p> Another aspect of the present invention is a cooling device. This device includes a fan motor and the above-mentioned motor drive device for driving the fan motor. According to this aspect, the noise generated from the fan motor can be reduced by gently changing the current flowing through the motor.</p><p> Yet another aspect of the present invention is an electronic device. This electronic device includes the cooling device described above. According to this aspect, the noise generated from the electronic device is reduced.</p><p> Yet another aspect of the present invention is a motor driving method. In this method, the steps of outputting the first and second sine wave signals that are opposite to each other according to the position of the rotor are compared with the first sine wave signal and the second sine wave signal, and the square wave signal is obtained. A step of outputting, a step of detecting the timing of phase switching based on the first and second sine wave signals, and a step of generating a pulse width modulated signal in which the duty ratio gradually changes for a predetermined period of phase switching. It includes a step of synthesizing a sine wave signal and a pulse width modulated signal by logical calculation to drive a motor to be driven.</p><p> According to this aspect, at the timing of phase switching, the energization period is controlled based on the pulse width modulation signal in which the duty ratio gradually changes, so that the regenerative current flowing through the coil can be changed gently. ..</p><p> It should be noted that any combination of the above components or components and expressions of the present invention that are mutually replaced between methods, devices, systems, and the like are also effective as aspects of the present invention.</p>

<p> According to the present invention, the coil current can be gradually changed at the timing of switching the phase of the motor.</p>

(First Embodiment) An embodiment of the present invention will be described with respect to a motor drive device used as a cooling device for cooling an electronic device such as a refrigerator or a personal computer. FIG. 1 is a circuit diagram showing a configuration of a cooling device 200 according to a first embodiment of the present invention. The cooling device 200 includes a motor drive device 100, a fan motor 110, and a Hall element 120.

The fan motor 110 is a single-phase full-wave motor and is arranged so as to face an object to be cooled (not shown). The rotation of the fan motor 110 is controlled by controlling the coil current, that is, the energized state by the drive voltage output from the motor drive device 100.

The Hall element 120 is connected to the power supply line to which the power supply voltage Vcc is applied via the resistor R10, and is grounded via the resistor R11. The magnitude of the signal output from the Hall element 120 is adjusted by the resistors R10 and R11. Therefore, depending on the common mode input range of the hysteresis comparator 10 and the amplifier 22, one or both of the resistors R10 and R11 may be short-circuited.

The Hall element 120 outputs a first sine wave signal Vs1 and a second sine wave signal Vs2 according to the position of the rotor of the fan motor 110. The first sine wave signal Vs1 and the second sine wave signal Vs2 are sine waves that are out of phase with each other and whose period changes according to the rotation speed of the fan motor 110. A power supply voltage Vcc is applied to the Hall element 120 via the resistor R10. The amplitudes of the first sine wave signal Vs1 and the second sine wave signal Vs2 output from the Hall element 120 can be adjusted by the resistor R10.

The motor drive device 100 drives the fan motor 110 based on the first sine wave signal Vs1 and the second sine wave signal Vs2 output from the Hall element 120. The motor drive device 100 is a functional IC integrally integrated on one semiconductor substrate. The motor drive device 100 drives the first input terminal 102, the second input terminal 104, and the fan motor 110 to which the first sine wave signal Vs1 and the second sine wave signal Vs2 are input, respectively, as terminals for signal input / output. The first output terminal 106 and the second output terminal 108 are provided, respectively, to output the first drive voltage Vdrv1 and the second drive voltage Vdrv2.

The motor drive device 100 includes a hysteresis comparator 10, a pulse width modulation signal generation circuit 20, and a drive circuit 30. The hysteresis comparator 10 compares the first sine wave signal Vs1 output from the Hall element 120 with the second sine wave signal Vs2, and is a square wave signal having a high level when Vs1&gt; Vs2 and a low level when Vs1 &lt;Vs2. Output Vrct.

The pulse width modulation signal generation circuit 20 detects the phase switching timing of the fan motor 110 based on the first sine wave signal Vs1 and the second sine wave signal Vs2 output from the Hall element 120, and determines the phase switching. Outputs a pulse width modulation signal Vpwm whose duty ratio gradually changes during the period.

The pulse width modulation signal generation circuit 20 includes an amplifier 22, a pulse width modulation comparator (hereinafter referred to as PWM comparator) 24, and an oscillator 26. The amplifier 22 amplifies the difference between the first sine wave signal Vs1 and the second sine wave signal Vs2 output from the Hall element 120 and outputs the absolute value signal Vabs. The oscillator 26 outputs a triangular or saw-like periodic voltage Vosc. The frequency of the periodic voltage Vosc generated by the oscillator 26 is sufficiently high with respect to the rotation speed of the fan motor 110, and it is desirable to set it to, for example, about several tens of kHz, more specifically, about 10 kHz to 40 kHz.

The PWM comparator 24 compares the absolute value signal Vabs output from the amplifier 22 with the periodic voltage Vosc, and outputs a pulse width modulation signal Vpwm which is a high level when Vabs&gt; Vosc and a low level when Vabs &lt;Vosc. This pulse width modulated signal Vpwm is a pulse width modulated signal having a constant frequency and changing between high level and low level periods according to the voltage value of the absolute value signal Vabs.

The square wave signal Vrct output from the hysteresis comparator 10 and the pulse width modulation signal Vpwm output from the pulse width modulation signal generation circuit 20 are input to the drive circuit 30. The drive circuit 30 drives the fan motor 110 by synthesizing the square wave signal Vrct and the pulse width modulation signal Vpwm by logical operation.

The drive circuit 30 includes a logic circuit 32, a pre-driver circuit 34, and an H-bridge circuit 36. The logic circuit 32 synthesizes the square wave signal Vrct and the pulse width modulation signal Vpwm by a logical operation. The logic circuit 32 outputs a signal obtained by logically inverting the square wave signal Vrct as the first signal Sig1 and outputs the square wave signal Vrct as the second signal Sig2 to the pre-driver circuit 34 in the subsequent stage. Further, in the logic circuit 32, the logical product of the pulse width modulated signal Vpwm and the square wave signal Vrct (Vrct Vpwm) is set as the third signal Sig3, and the logical product of the pulse width modulated signal Vpwm and the inverted signal of the square wave signal Vrct ( * VrctVpwm) is output as the 4th signal Sig4. The * attached to each signal in the present specification represents a logical inversion.

The H-bridge circuit 36, which is the output stage of the drive circuit 30, includes a first high-side switch MH1, a second high-side switch MH2, a first low-side switch ML1, and a second low-side switch ML2. The first high-side switch MH1 and the second high-side switch MH2 are P-channel MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), and the first low-side switch ML1 and the second low-side switch ML2 are N-channel MOSFETs.

The first high-side switch MH1 and the first low-side switch ML1 are connected in series between the power supply line to which the power supply voltage Vdd is applied and the ground. The voltage at the connection point of the first high-side switch MH1 and the second low-side switch ML2 is applied to one end of the fan motor 110 as the first drive voltage Vdrv1 via the first output terminal 106. The on / off state of the first high-side switch MH1 and the first low-side switch ML1 is controlled by the gate control signals SH1 and SL1 input to each gate. That is, the first high-side switch MH1 is turned on when the gate control signal SH1 is at a low level and turned off when the gate control signal SH1 is at a high level. The first low-side switch ML1 is turned on when the gate control signal SL1 is at a high level and turned off when the gate control signal SL1 is at a low level.

The first drive voltage Vdrv1 applied to the fan motor 110 becomes the power supply voltage Vdd when the first high-side switch MH1 is on and the first low-side switch ML1 is off, and the first high-side switch MH1 is off and the first low-side switch. When ML1 is on, the ground potential is 0V.

Similarly, the second high-side switch MH2 and the second low-side switch ML2 are also connected in series between the power line and ground. The voltage at the connection point of the second high-side switch MH2 and the second low-side switch ML2 is applied to the other end of the fan motor 110 as the second drive voltage Vdrv2 via the second output terminal 108.

The pre-driver circuit 34 generates gate control signals SH1, SH2, SL1, and SL2 based on the first signal Sig1 to the fourth signal Sig4 output from the logic circuit 32. In this embodiment, SL1 = Sig1, SL2 = Sig2, SH1 = * Sig3, SH2 = * Sig4 are set. That is, in the present embodiment, the pre-driver circuit 34 drives the first low-side switch ML1 and the second low-side switch ML2 by alternately turning them on and off based on the square wave signal Vrct. Further, the pre-driver circuit 34 drives the first high-side switch MH1 and the second high-side switch MH2 by alternately turning them on and off based on the logical product of the pulse width modulation signal Vpwm and the square wave signal Vrct.

The operation of the cooling device 200 configured as described above will be described with reference to FIG. FIG. 2 is a time chart showing the operating state of the cooling device 200 of FIG. The time chart of FIG. 2 shows the first sine wave signal Vs1 and the second sine wave signal Vs2, the absolute value signal Vabs and the periodic voltage Vosc, the pulse width modulation signal Vpwm, the square wave signal Vrct, and the first signal Sig1 ~ The 4th signal Sig4 and coil current Icon are shown. Further, in the figure, for the sake of brevity, the vertical axis and the horizontal axis are shown enlarged or reduced as appropriate.

From the Hall element 120, the first sine wave signal Vs1 and the second sine wave signal Vs2, which are out of phase with each other, are output according to the position of the rotor. The square wave signal Vrct output from the hysteresis comparator 10 has a high level when Vs1&gt; Vs2 and a low level when Vs1 &lt;Vs2.

The absolute value signal Vabs output from the amplifier 22 is obtained by amplifying the difference | Vs1-Vs2 | between the first sine wave signal Vs1 and the second sine wave signal Vs2, and has a component proportional to | Vs1-Vs2 | and a direct current. It becomes the voltage on which the components are superimposed. As a result, the absolute value signal Vabs takes the minimum value at the timing of phase switching, as shown in FIG. The pulse width modulation signal Vpwm output from the PWM comparator 24 is high level when Vabs&gt; Vosc and low level when Vabs &lt;Vosc. Hereinafter, the period in which the pulse width modulation signal Vpwm repeats high level and low level according to the frequency of the periodic voltage Vosc is referred to as a soft start period (corresponding to Tx in Fig. 2), and the pulse width modulation signal Vpwm becomes high level or low level. The fixed period is called the energization period (corresponding to Ty in the figure).

In the soft start period, the pulse width modulated signal Vpwm has the longest low-level period at the phase switching timing (zero cross point) where the absolute value signal Vabs is the minimum, and the low-level period centered on the zero cross point. It is getting shorter and shorter.

As described above, the first signal Sig1 generated by the logic circuit 32 is a signal obtained by inverting the square wave signal Vrct, and the second signal Sig2 is a signal obtained by inverting the square wave signal Vrct. The third signal Sig3 is the logical product of the square wave signal Vrct and the pulse width modulation signal Vpwm, and the fourth signal Sig4 is the logical product of the inverted signal of the square wave signal Vrct and the pulse width modulation signal Vpwm. Therefore, the high-level period of the third signal Sig3 and the fourth signal Sig4 gradually increases from the zero crossing point, respectively.

The first high-side switch MH1 is on when the gate control signal SH1 is low level, off when it is high level (that is, on when the third signal Sig3 is high level, off when it is low level), and is the second low-side switch. ML2 is on when the gate control signal SL2 is high level and off when the gate control signal SL2 is low level. Therefore, during the period from time T0 to T1 in FIG. 2, the first high-side switch MH1 repeats on / off according to the pulse width signal while the second low-side switch ML2 is on. At this time, the coil current Icon flows in the direction from the first output terminal 106 of the motor drive device 100 to the second output terminal 108.

Similarly, the first low-side switch ML1 is on when the gate control signal SL1 is high level and off when the gate control signal SL1 is low level, and the second high-side switch MH2 is on when the gate control signal SH2 is low level and is high level. When it is off (that is, it is on when the fourth signal Sig4 is at a high level and off when it is at a low level). Therefore, during the period from time T1 to T2, the second high-side switch MH2 repeats on / off according to the pulse width signal while the first low-side switch ML1 is on. At this time, the coil current Icon flows in the direction from the second output terminal 108 of the motor drive device 100 to the first output terminal 106.

As described above, according to the motor drive device 100 according to the present embodiment, the coil current Icon is obtained by driving the fan motor 110 based on the pulse width modulation signal Vpwm at the timing of phase switching. As shown by the solid line in 2, it will change gradually. As a result, the generation of noise is reduced, and the peak of the coil current Icon can be suppressed.

In order to clarify the effect of the motor drive device 100 according to the present embodiment, the time waveform of the coil current Icon when the fan motor 110 is driven without using the pulse width modulation signal at the timing of phase switching. Is indicated by a broken line. When all the transistors MH1, MH2, ML1 and ML2 constituting the H-bridge circuit 36 are turned off at the timing of phase switching without using the pulse width modulation signal, the coil current Icon is passed through a flywheel diode (not shown). Will flow. Since the coil current Icoil cannot be controlled during the non-energized period in which all the transistors are turned off, the coil current Icoil has a peak as shown by the broken line in FIG. When the coil current Icon flows through the flywheel diode toward the power supply line, a very large voltage is applied to the transistors constituting the H-bridge circuit 36, which may affect the reliability of the device. .. According to the motor drive device 100 according to the present embodiment, such a problem can be suitably solved.

(Second embodiment) In the first embodiment, the case where the single-phase motor is linearly driven during the energization period has been described, but in the second embodiment below, the case where the single-phase motor is switched and driven will be described. FIG. 3 is a circuit diagram showing the configuration of the cooling device 200 according to the second embodiment. In FIG. 3, the same or equivalent components as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

A temperature detection circuit 130 that generates a temperature detection voltage Vth depending on the ambient temperature of the object to be cooled is connected to the outside of the motor drive device 100. The temperature detection circuit 130 includes a thermistor Rth and a resistor R12 connected in series between the reference voltage and ground. The voltage at the connection point between the thermistor Rth and the resistor R12 is input to the control terminal 103 of the motor drive device 100 as the temperature detection voltage Vth. This temperature detection voltage Vth is input to the pulse width modulation signal generation circuit 20 together with the first sine wave signal Vs1 and the second sine wave signal Vs2 output from the Hall element 120.

The pulse width modulation signal generation circuit 20 includes a comparator 28 that compares the temperature detection voltage Vth with the periodic voltage Vosc output from the oscillator 26. The comparator 28 generates a temperature pulse width modulation signal Vpwmth that has a high level when Vosc&gt; Vth and a low level when Vosc &lt;Vth. This temperature pulse width modulation signal Vpwmth is output to the drive circuit 30.

The drive circuit 30 logically operates and synthesizes the temperature pulse width modulation signal Vpwmth, the pulse width modulation signal Vpwm output from the PWM comparator 24, and the square wave signal Vrct, and drives the fan motor 110. The logic circuit 32 sets the logical product of the pulse width modulation signal Vpwm output from the PWM comparator 24 and the temperature pulse width modulation signal Vpwmth output from the comparator 28 as the pulse width modulation signal Vpwm', and sets this pulse width modulation signal Vpwm. 'And the square wave signal Vrct are logically calculated to generate the first signal Sig1 to the fourth signal Sig4. The synthesis of the pulse width modulation signal Vpwm'and the square wave signal Vrct may be performed in the same manner as the synthesis of the pulse width modulation signal Vpwm and the square wave signal Vrct in the first embodiment.

According to the motor drive device 100 according to the second embodiment configured as described above, the temperature can be reflected in the rotation control of the fan motor 110.

(Third embodiment) In the third embodiment, the cooling device 200 that controls the fan motor 110 based on the pulse width modulated control signal Vcnt that controls the rotation speed of the fan motor 110 to be driven, not the temperature, will be described. In the present embodiment, the configuration of the motor drive device 100 is the same as that in FIG. 3, and a smoothing circuit 140 is provided instead of the temperature detection circuit 130. FIG. 4 is a circuit diagram showing a configuration of a smoothing circuit 140 of the cooling device 200 according to the third embodiment.

This smoothing circuit 140 smoothes the pulse width-modulated control signal Vcnt that controls the rotation speed of the fan motor 110, and outputs it as a DC rotation control voltage Vcnt'. The smoothing circuit 140 includes a transistor Q1, a capacitor C1, and a resistor R14. The control signal Vcnt is input to the base of the transistor Q1, and the emitter is grounded. Capacitor C1 is connected between the collector of transistor Q1 and ground. The voltage appearing in the collector of the transistor Q1 is input to the control terminal 103 of the motor drive device 100 as the rotation control voltage Vcnt'.

According to the cooling device 200 according to the present embodiment, the rotation control of the fan motor 110 can be controlled according to the duty ratio of the control signal Vcnt input from the outside. That is, the smoothing circuit 140 of FIG. 4 outputs a rotation control voltage Vcnt', which decreases the voltage value as the duty ratio of the control signal Vcnt increases. When the rotation control voltage Vcnt'is lowered, the duty ratio of the temperature pulse width modulation signal Vpwmth output from the comparator 28 is increased, so that the fan motor 110 can be rotated at a high rotation speed.

The above-described embodiment is an example, and it is understood by those skilled in the art that various modifications are possible for each of these components and combinations of each processing process, and that such modifications are also within the scope of the present invention. is there.

In the first to third embodiments described above, the gain of the amplifier 22 may be configured to be adjustable by an external resistor. By adjusting the gain of the amplifier 22, the magnitude of the absolute value signal Vabs can be controlled. When the gain of the amplifier 22 is increased, the absolute value signal Vabs shown in FIG. 2 shifts to the high potential side, so that the energization period Ty becomes long and the soft start period Tx becomes short. On the contrary, when the gain of the amplifier 22 is reduced, the absolute value signal Vabs shown in FIG. 2 shifts to the low potential side, so that the energization period Ty becomes short and the soft start period Tx becomes long.

In the embodiment, the case where the motor driving device 100 drives a single-phase full-wave motor has been described, but the present invention is not limited thereto. Even in a multi-phase motor, the coil current can be gradually changed by providing a soft start period at the timing of phase switching and generating and driving a pulse width modulation signal.

In the embodiment, the case where the motor drive device 100 is integrated into one LSI has been described, but the present invention is not limited to this, and some components are provided outside the LSI as discrete elements or chip components. , Or it may be composed of a plurality of LSIs. For example, the H-bridge circuit 36 of the drive circuit 30 may be configured by using discrete power transistors.

In the embodiment, among the transistors constituting the H-bridge circuit 36, the low-side switch is driven based on the square wave signal Vrct, and the high-side switch is driven based on the pulse width modulation signal Vpwm and the square wave signal Vrct. The invention is not limited to this. For example, the pre-driver circuit 34 may drive both the high-side switch and the low-side switch based on the pulse width modulation signal Vpwm and the square wave signal Vrct. That is, the gate control signal SL1 may be the fourth signal Sig4, and the gate control signal SL2 may be the third signal Sig3.

Further, the transistor used in the embodiment may replace the bipolar transistor and the FET with each other.

The setting of the high level and low level logical values described in the embodiment is an example, and can be freely changed by appropriately inverting it with an inverter or the like.

<figref num="1">It is a circuit diagram which shows the structure of the cooling apparatus which concerns on 1st Embodiment.</figref><figref num="2">It is a time chart which shows the operating state of the cooling device of FIG.</figref><figref num="3">It is a circuit diagram which shows the structure of the cooling apparatus which concerns on 2nd Embodiment.</figref><figref num="4">It is a circuit diagram which shows the structure of the smoothing circuit of the cooling apparatus which concerns on 3rd Embodiment.</figref>

Code description

100 motor drive, 10 hysteresis comparator, 20 pulse width modulation signal generation circuit, 22 amplifier, 24 PWM comparator, 26 oscillator, 28 comparator, 30 drive circuit, 32 logic circuit, 34 pre-driver circuit, 36 H bridge circuit, MH1 1 High side switch, MH2 2nd high side switch, ML1 1st low side switch, ML2 2nd low side switch, 110 fan motor, 120 hole element, 130 temperature detection circuit, 140 smoothing circuit, 200 cooling device, Vpwm pulse width modulation signal , Vrct square wave signal, Vabs absolute value signal, Vs1 first sine wave signal, Vs2 second sine wave signal, Vpwmth temperature pulse width modulation signal.