JP4979476B2 - Motor speed control circuit - Google Patents

Description

  The present invention relates to a motor speed control circuit.

  In recent years, an integrated circuit such as a CPU (Central Processing Unit) used in electronic devices has increased in heat generation as its operation speed increases. An increase in the amount of heat generated by the CPU causes problems such as thermal runaway in the CPU. Therefore, electronic devices are generally provided with a fan for cooling the CPU.

  FIG. 8 shows an example of a block diagram of a motor speed control circuit that controls the rotational speed of a fan motor for cooling the CPU (see Patent Document 1). More specifically, the reference voltage circuit 700 receives a speed control signal from a microcomputer or the like corresponding to the target rotational speed of the motor 500 and a temperature signal from a thermistor corresponding to the temperature around the CPU. A reference voltage corresponding to the signal is output. Further, an FG (Frequency Generator) signal corresponding to the rotational speed of the motor 500 is input to the speed voltage output circuit 701, and a speed voltage corresponding to the FG signal is output. The comparison circuit 702 compares the reference voltage with the speed voltage and outputs a drive signal that is a comparison result. The motor drive circuit 703 drives the motor 500 based on the drive signal so that the speed voltage matches the reference voltage.

Here, based on the embodiment disclosed in Patent Document 1, the relationship between the rotational speed of the motor 500, the speed control signal, and the temperature in the motor speed control circuit 600 of FIG. 8 is illustrated as shown in FIG. Become. In addition, T1-T3 in FIG. 9 shows temperature, and has a relationship of T1 <T2 <T3. Further, the speed control signal input to the motor speed control circuit 600 is a PWM (Pulse Wide Modulation) signal, and the rotational speed of the motor 500 increases according to the duty ratio of the H level (high level) of the PWM signal. . Since the motor speed control circuit 600 generates a speed voltage by feeding back an FG signal corresponding to the rotational speed of the motor 500 and compares it with a reference voltage, the rotational speed of the motor is the duty of the H level of the PWM signal. It varies linearly with the ratio. Further, even when the H-level duty ratio of the PWM signal is constant, the rotational speed of the motor increases as the temperature rises.
JP 2007-68344 A

  However, in a motor that rotates a fan in recent years, the rotation speed of the motor is linearly changed with respect to the speed control signal, the rotation speed of the motor is changed according to the temperature, and the rotation speed of the motor is minimized. When a speed control signal is input, it is required to minimize the rotational speed of the motor regardless of the temperature. The motor speed control circuit 600 shown in FIG. 8 changes the rotational speed of the motor 500 as the temperature changes even when a PWM signal is inputted to minimize the rotational speed as shown in FIG. Resulting in.

  In order to achieve the above object, the motor speed control circuit of the present invention outputs the rotation speed and the speed voltage corresponding to the temperature based on the speed signal corresponding to the rotation speed of the motor and the temperature signal corresponding to the temperature. A speed voltage circuit, a comparison circuit that compares a reference voltage corresponding to a target rotational speed of the motor and the speed voltage, and a voltage level of the speed voltage based on a comparison result of the comparison circuit. And a drive circuit for driving the motor to match the voltage level.

  The motor speed is changed linearly with respect to the speed control signal, the motor speed is changed according to the temperature, and when the speed control signal is input to minimize the motor speed, the temperature is Nevertheless, it is possible to provide a motor speed control circuit capable of minimizing the rotation speed of the motor.

  At least the following matters will become apparent from the description of this specification and the accompanying drawings.

  FIG. 1 is a diagram showing a configuration of a motor speed control circuit 10 according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an embodiment of the reference voltage circuit 20. FIG. 3 is a diagram illustrating an embodiment of the temperature / current generation circuit 30 to which the thermistor RTH is connected. FIG. 4 is a diagram illustrating an embodiment of the speed voltage output circuit 31. FIG. 5 is a diagram illustrating an embodiment of the comparison circuit 22. The motor speed control circuit 10 of the present embodiment will be described with reference to FIGS.

  The motor speed control circuit 10 is based on a speed control signal corresponding to the target rotational speed of the motor 11 input from the microcomputer, a temperature signal corresponding to the temperature, and a speed signal corresponding to the actual rotational speed of the motor 11. , A circuit for controlling the rotation speed of the motor 11, and is composed of a reference voltage circuit 20, a speed voltage circuit 21, a comparison circuit 22, and a motor drive circuit 23.

  The motor 11 is a motor that rotates a fan for cooling the CPU and the like, and a rotary motor or the like can be adopted.

  First, the outline of each circuit constituting the motor speed control circuit 10 shown in FIG. 1 will be described. The reference voltage circuit 20 is a circuit that outputs a reference voltage Vref corresponding to a target rotation speed when a speed control signal is input. In the present embodiment, the input speed control signal is a PWM signal, and the reference voltage Vref decreases when the duty ratio of the H level (high level) of the PWM signal is large, and the duty ratio of the H level of the PWM signal is Rise when small. The speed voltage circuit 21 is a circuit that outputs a speed voltage Vv corresponding to the speed signal and the temperature signal, and includes a temperature current generation circuit 30 and a speed voltage output circuit 31. In the present embodiment, the speed signal is an FG signal having a frequency corresponding to the rotational speed of the motor. The temperature current generation circuit 30 is a circuit that outputs a temperature current Ith corresponding to the temperature when a temperature signal is input. The temperature current Ith increases as the temperature rises, and the temperature current Ith decreases as the temperature falls. To do. The speed voltage output circuit 31 is a circuit that outputs a speed voltage Vv corresponding to the product of the cycle of the FG signal and the temperature current Ith. When the rotation speed of the motor 11 is high, the speed voltage Vv decreases and the motor 11 When the rotation speed is low, the speed voltage Vv increases. The comparison circuit 22 is a circuit that compares the reference voltage Vref and the speed voltage Vv and outputs a drive signal Vdr that is a comparison result. The motor drive circuit 23 is a circuit that drives the motor 11 in accordance with the drive signal Vdr. In the present specification, when the speed voltage Vv is higher than the reference voltage Vref, the acceleration control state for accelerating the motor 11 is set, and when the speed voltage Vv is lower than the reference voltage Vref, the deceleration control state for decelerating the motor 11 is set. .

  By configuring the motor speed control circuit 10 as described above, the speed voltage Vv of the motor speed control circuit 10 is controlled to coincide with the reference voltage Vref.

  As shown in FIG. 2, the reference voltage circuit 20 includes PNP transistors Q1 and Q2, NPN transistors Q3 to Q8, resistors R1 to R3, a capacitor C1, and bias current sources I1 to I4.

  As shown in FIG. 3, the temperature current generation circuit 30 includes PNP transistors Q10, Q12, Q13 (transistors), an NPN transistor Q11, and a bias current source I5. 3 is a thermistor RTH, and one end of the thermistor RTH is connected to the emitter electrode of the NPN transistor Q11. The PNP transistor Q12 and the NPN transistor Q11 correspond to the temperature voltage output circuit of the present invention.

  As shown in FIG. 4, the speed voltage output circuit 31 includes PNP transistors Q31, Q32, Q36, and Q40, NPN transistors Q30, Q33 to Q35, and Q37 to Q39, resistors R6 to R8, a capacitor C2, and bias current sources I6 to I8. , An edge circuit 60 and an integration circuit 70. The capacitor C2 corresponds to the capacitor of the present invention, and the edge circuit 60 and the NPN transistor Q30 correspond to the discharge circuit of the present invention.

  As shown in FIG. 5, the comparison circuit 22 includes PNP transistors Q43 to Q45, Q48, Q49, Q52, Q54, NPN transistors Q41, Q42, Q46, Q47, Q50, Q51, Q53, Q55, and bias current sources I9 to I12. Consists of

  The motor drive circuit 23 is not illustrated in the present specification, but an H bridge circuit, for example, can be used.

  When a PWM signal is input to the motor speed control circuit 10 as a speed control signal from a microcomputer or the like at a predetermined temperature Ta, and the motor 11 is rotating at a rotation speed corresponding to the predetermined temperature Ta and an H level duty ratio in the PWM signal. Will be described.

  In the reference voltage circuit 20, as shown in FIG. 2, the PNP transistors Q1 and Q2, the NPN transistors Q3 and Q4, and the bias current source I1 constitute a comparator, and the base electrode of the PNP transistor Q1 is a non-inverting input. The base electrode of the PNP transistor Q2 corresponds to the inverting input. A divided voltage V1 divided by resistors R1 and R2 connected in series between the power supply VDD and the ground GND is applied to the base electrode of the PNP transistor Q2.

  When the PWM signal is at the H level, when it is input to the base electrode of the PNP transistor Q1, that is, when the potential of the base electrode of the PNP transistor Q1 is higher than the divided voltage V1, the potential of the collector electrode of the NPN transistor Q4 is at the H level. Thus, the NPN transistor Q5 is turned on. When the NPN transistor Q5 is turned on, the bias current from the bias current source I2 flows to the NPN transistor Q5, the NPN transistor Q7 is turned off, and the NPN transistor Q8 is turned on. Therefore, the potential of the node where the resistor R3 and the capacitor C1 are connected is almost zero.

  On the other hand, when the PWM signal is at the L level (low level), when it is input to the PNP transistor Q1, that is, when the potential of the base electrode of the PNP transistor Q1 is lower than the divided voltage V1, the operation opposite to that described above is performed. Since the NPN transistor Q8 is turned off, the bias current from the bias current source I4 flows into the capacitor C1, and the capacitor C1 is charged.

  The resistor R3 and the capacitor C1 constitute an LPF (Low Pass Filter), and smoothes the voltage input to the LPF, that is, the voltage of the collector electrode of the NPN transistor Q8 that changes depending on whether the NPN transistor Q8 is turned on or off. As a result, the smoothed reference voltage Vref is output to the node where the resistor R3, which is the output of the LPF, and the capacitor C1 are connected. This voltage Vref decreases when the H level duty ratio of the PWM signal is large, and increases when the H level duty ratio of the PWM signal is small.

  In the temperature current generating circuit 30, as shown in FIG. 3, since the PNP transistor Q10 and the bias current source I5 constitute an emitter follower, the voltage VEF corresponding to Vbias1 applied to the base electrode of the PNP transistor Q10 is , Output from the emitter electrode of the PNP transistor Q10. Here, if the bias voltage Vbias1 applied to the base electrode of the PNP transistor Q10 is a voltage whose change in voltage value is small due to a temperature change such as a band gap reference voltage, the voltage VEF is also a voltage value with respect to the temperature change. The change of becomes smaller. The thermistor RTH corresponds to the emitter resistance of the NPN transistor Q11. Since the voltage VEF described above is applied to the base electrode of the NPN transistor Q11, the current flowing through the thermistor RTH is determined by the resistance value RTH (Ta) of the thermistor corresponding to the temperature Ta. As a result, the voltage signal VTH (Ta) generated in the thermistor RTH is input to the temperature current generation circuit 30 as a temperature signal. Since the PNP transistor Q12 and the PNP transistor Q13 form a current mirror, a temperature current Ith corresponding to the current flowing through the thermistor RTH (Ta) is output from the PNP transistor Q13. If the temperature coefficient of the thermistor RTH in this embodiment is negative, the temperature current Ith increases as the temperature rises, and the temperature current Ith decreases as the temperature falls.

  In the speed voltage output circuit 31, as shown in FIG. 4, the temperature current Ith from the temperature current generation circuit 30 is supplied to a node to which the bias current source I6 and the capacitor C2 are connected. The edge circuit 60 changes the output edge signal VED into a short pulse by detecting the edge of the input pulse signal. FIG. 6 is a diagram showing waveforms of main signals in the speed voltage output circuit 31, and will be referred to as appropriate. First, when the FG signal is input to the edge circuit 60, as described above, the edge signal VED is changed to a short pulse at the edge of the FG signal. Since the edge signal VED is input to the base electrode of the NPN transistor Q30, the NPN transistor Q30 is turned on or off depending on the level of the edge signal.

  When the edge signal VED is at the L level, the NPN transistor Q30 is off, and the capacitor C2 is charged with the sum of the temperature current Ith and the bias current Ibias1 for the period TA. Assuming that the node voltage of the node to which the temperature current Ith and the bias current Ibias1 are supplied is V2, the current value of the bias current Ibias1 is Ibias1, and the capacitance value of the capacitor C2 is C, only the period Tx from time Ts when VED becomes L level. The node voltage V2 at the elapsed time Tp is represented by V2 (Tx) = ((Ith + Ibias1) × Tx) / C. First, an operation when the node voltage V2 is higher than the divided voltage V3 in the resistors R4 to R6 connected in series between the power supply VDD and the ground GND will be described. Note that the period TB is a period in which the relationship of the node voltage V2> the divided voltage V3 is satisfied. Since the PNP transistors Q31 and Q32, the NPN transistors Q33 and Q34, and the bias current source I7 constitute a comparator, the potential of the collector electrode of the NPN transistor Q33 becomes L level. Accordingly, the NPN transistor Q35 is turned off, the NPN transistor Q38 is turned on, and the NPN transistor Q39 is turned off. Since the bias voltage Vbias2 that turns on the PNP transistor Q40 is applied to the base electrode of the PNP transistor Q40, the output voltage Vo becomes H level. In the present embodiment, the H level output voltage Vo is the power supply voltage VDD. When the node voltage V2 is lower than the divided voltage V3, the operation is the reverse of the above operation, and the NPN transistor Q39 is finally turned on. Here, the on resistance of the PNP transistor Q40 is designed to be larger than the on resistance of the NPN transistor Q39, and the output voltage Vo becomes L level. In this embodiment, the L level output voltage Vo is 0 (zero) V.

  On the other hand, when the edge signal VED is at the H level, the NPN transistor Q30 is turned on, so that the node voltage V2 becomes lower than the divided voltage V3. Therefore, the same operation as when the node voltage V2 is lower than the divided voltage V3 is performed, and as a result, the output voltage Vo becomes L level. In addition, when the edge signal VED is at the H level and the node signal V2 is lower than the divided voltage V3 when the edge signal VED is at the L level, the period TC is indicated.

  From the above description, if the period during which the edge signal VED is at the H level is sufficiently short and ignored, the output voltage Vo has a period of the period TA. Therefore, it can be seen that the output voltage Vo can be expressed as Vo = VDD × (TB / TA). Further, there is a relationship of TA = TB + TC between the periods TA, TB, TC, and V3 = V2 (TC) = ((Ith + Ibias1) × TC) / between the divided voltage V3 and the period TC. There is a relationship of C. From the above relationship, when the output voltage Vo is arranged, Vo = VDD × (1− (C × V3) / (TA × (Ith + Ibias1))). That is, the output voltage Vo is a voltage corresponding to the product of the temperature current Ith and the L level period TA of the edge signal VED. Further, the temperature current Ith changes according to the temperature, and the period TA of the L level of the edge signal VED changes according to the cycle of the FG signal, that is, the rotational speed of the motor. It can be seen that the voltage is in accordance with the product of the rotational speeds. Further, since the temperature current Ith is constant at the predetermined temperature Ta, the width in which the output voltage Vo becomes L level is constant. When the rotation speed of the motor 11 is high, the width of the L level in one cycle of the output voltage Vo becomes large, and the output voltage Vo decreases. When the rotation speed of the motor 11 is low, the width of the L level shown in one cycle of the output voltage Vo becomes small and the output voltage Vo rises. The integrating circuit 70 outputs the speed voltage Vv corresponding to the H level of the output voltage Vo by integrating the output voltage Vo. Therefore, the speed voltage Vv decreases when the rotation speed of the motor 11 is high, and the speed voltage Vv increases when the rotation speed of the motor 11 is low.

  As shown in FIG. 5, the reference voltage Vref and the speed voltage Vv are input to the comparison circuit 22. As described above, in this specification, when the speed voltage Vv is higher than the reference voltage Vref, the motor 11 is accelerated, and when the speed voltage Vv is lower than the reference voltage Vref, the motor 11 is decelerated. State.

  First, the operation of the comparison circuit 22 in the acceleration control state will be described. NPN transistors Q41, Q42, Q46, Q47, PNP transistors Q43, Q44, Q45, Q48, and bias current source I9 constitute a comparator. The base electrode of the NPN transistor 41 corresponds to the non-inverting input of the comparator, and the base electrode of the NPN transistor 42 corresponds to the inverting input of the comparator. Therefore, in the acceleration control state, the NPN transistor Q49 is turned off, the NPN transistor Q50 is turned on, and the NPN transistor Q51 is turned on. Furthermore, since the bias current source I12 is set so that the PNP transistor Q54 is turned on and the NPN transistor Q55 is turned off when the NPN transistor Q51 is turned on, the drive signal Vdr becomes L level. On the other hand, in the deceleration control state, the operation reverse to the acceleration control state is performed, so that the drive signal Vdr finally becomes H level.

  The motor drive circuit 23 is driven to accelerate the motor 11 when an L level drive signal Vdr is input, and is driven to decelerate the motor 11 when an H level drive signal Vdr is input.

  Here, the FG signal in the acceleration control state will be described. In the acceleration control state, since the rotation speed of the motor 11 is accelerated, the pulse period of the FG signal corresponding to the rotation speed of the motor 11 is shortened, and the period occupied by the L level in the output voltage Vo increases. Therefore, the speed voltage Vv decreases so as to coincide with the reference voltage Vref. On the other hand, in the deceleration control state, since the rotation speed of the motor 11 is decelerated, the pulse period of the FG signal corresponding to the rotation speed of the motor 11 is increased, and the period occupied by the L level in the output voltage Vo is decreased. Therefore, the speed voltage Vv rises to match the reference voltage Vref. Thus, since the motor speed control circuit 10 feeds back the speed voltage Vv and controls the rotation speed of the motor 11 so as to match the level of the reference voltage Vref, the rotation speed of the motor 11 is the reference voltage Vref, and further It has a linear relationship with the duty ratio of the H level of the PWM signal.

  The operation of the motor speed control circuit 10 when the H level duty ratio in the PWM signal is zero at the predetermined temperature Ta will be described. When a PWM signal having an H level duty ratio of zero is input to the reference voltage circuit 20, the base electrode of the PNP transistor Q1 becomes L level, so that the voltage Vref smoothed by the LPF becomes almost the power supply voltage VDD. . At this time, since the speed voltage Vv is lower than the reference voltage Vref, the motor speed control circuit 10 enters a deceleration control state. Accordingly, the motor speed control circuit 10 decelerates the motor 11 so that the speed voltage Vv matches the reference voltage Vref. In order to set the speed voltage Vv to the power supply voltage VDD, it is necessary to stop the H level pulse in the FG signal, and as a result, the motor 11 is stopped. Therefore, when the H level duty ratio of the PWM signal is zero, the rotational speed of the motor is zero regardless of the temperature.

  The operation of the motor speed control circuit 10 when the H level duty ratio of the PWM signal is a predetermined duty ratio and the temperature changes from the predetermined temperature Ta will be described. FIG. 7 is a diagram showing the relationship between the rotational speed of the motor and the speed control signal at different temperatures when the motor 11 is driven by the motor speed control circuit 10 to which the present invention is applied. When the temperature rises, the resistance value of the thermistor RTH becomes small, and the temperature current Ith increases. As a result, the period during which the node voltage V2 becomes higher than the divided voltage V3 increases, the width of the L level in one cycle of the output voltage Vo decreases, and the speed voltage Vv becomes higher than the reference voltage Vref. Since this is the acceleration control state described above, the motor speed control circuit 10 controls the rotation speed of the motor 11 to increase. As a result, the pulse period of the FG signal corresponding to the rotation speed of the motor 11 is shortened, and the period occupied by the L level in the output voltage Vo increases. As a result, the speed voltage Vv decreases so as to coincide with the reference voltage Vref.

  On the other hand, when the temperature is lower than the predetermined temperature Ta, the temperature current Ith decreases. As a result, the period during which the node voltage V2 is lower than the divided voltage V3 increases, and as a result, the output voltage Vo becomes lower than the reference voltage Vref. In this case, the operation is reverse to the above-described operation, and the deceleration control state is set. Therefore, the rotation speed of the motor 11 is decelerated, and the pulse period of the FG signal corresponding to the rotation speed of the motor 11 is lengthened. That is, the period occupied by the L level in the output voltage Vo decreases, and the speed voltage Vv increases so as to match the reference voltage Vref.

  In this way, even if the H-level duty ratio of the PWM signal is a predetermined duty ratio, the speed voltage Vv changes as the temperature increases, and the rotational speed of the motor, that is, the rotational speed of the fan increases. On the other hand, when the temperature decreases, similarly, the motor speed control circuit 10 can reduce the rotation speed of the fan by decreasing the rotation speed of the motor.

  The motor speed control circuit 10 to which the present embodiment having the above-described configuration is applied changes the rotational speed of the motor 11 linearly with respect to the duty ratio of the H level of the PWM signal, and responds to the temperature and the rotational speed of the motor. When the PWM signal having the H level duty ratio of zero is input to stop the motor 11, the rotation speed of the motor 11 is set to zero regardless of the temperature.

  Further, in Patent Document 1, a divided voltage (hereinafter referred to as a series resistor) is connected to a thermistor, and a divided voltage generated by applying a voltage to the series resistor is input to the motor speed control integrated circuit as a temperature signal. is doing. From the viewpoint of reducing the number of parts, it is preferable to realize the series resistance in the motor speed integrated circuit, but it is difficult to control the resistance value and the temperature coefficient of the resistance in the integrated circuit. Therefore, it is necessary to use discrete components for the series resistance. On the other hand, in this embodiment, by connecting the thermistor RTH to the emitter electrode of the NPN transistor Q11, the voltage signal VTH (Ta) generated in the thermistor RTH is input to the motor speed control circuit 10 as a temperature signal. Thereby, in this embodiment, in order to input a temperature signal, it is sufficient to use only the thermistor RTH, and the number of parts can be reduced as compared with the case described above.

  In addition, the said Example is for making an understanding of this invention easy, and is not for limiting and interpreting this invention. The present invention can be changed and improved without departing from the gist thereof, and the present invention includes equivalents thereof.

  For example, in this embodiment, the PWM signal is a speed control signal, but an analog signal may be a speed control signal. In this case, an analog signal may be directly input to the comparison circuit 22 instead of the reference voltage Vref in the present embodiment.

  In this embodiment, the speed voltage Vv is generated by charging the capacitor C2 with the temperature current Ith. However, the temperature current Ith is not supplied to the speed voltage output circuit 31, and the speed voltage output circuit 31 of this embodiment is used. The output speed voltage Vv may be used as the bias voltage. In this case, instead of the temperature current generation circuit 30, the above-mentioned bias voltage is applied to one end of a resistor in which a thermistor and a resistor are connected in series, whereby the divided voltage between the thermistor and the resistor is converted into a speed voltage. Vv. The speed voltage Vv generated by the divided voltage of the thermistor and the resistance is a voltage corresponding to the product of the bias voltage and the resistance ratio including the thermistor resistance. Therefore, the speed voltage Vv corresponding to the rotational speed and temperature of the motor can be generated, and the same effects as those described in the present embodiment can be obtained.

It is a figure which shows the structure of the motor speed control circuit 10 which is one Embodiment of this invention. 2 is a diagram illustrating an embodiment of a reference voltage circuit 20. FIG. It is a figure which shows one Embodiment of the temperature current generation circuit 30 to which the thermistor RTH was connected. FIG. 3 is a diagram illustrating an embodiment of a speed voltage output circuit 31. 3 is a diagram illustrating an embodiment of a comparison circuit 22. FIG. FIG. 4 is a diagram illustrating waveforms of main signals in the speed voltage output circuit 31. It is a figure which shows the relationship between the rotational speed of a motor in a different temperature, and a speed control signal at the time of driving the motor 11 by the motor speed control circuit 10 to which this invention is applied. It is a figure which shows an example of the block diagram of the conventional motor speed control circuit. It is a figure which shows the relationship between the rotational speed of the motor in the different temperature in the conventional motor speed control circuit, and a speed control signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Motor speed control circuit 11 Motor 20 Reference voltage circuit 21 Speed voltage circuit 22 Comparison circuit 23 Motor drive circuit 30 Temperature current generation circuit 31 Speed voltage output circuit 60 Edge circuit 70 Integration circuit

Claims (5)

A speed voltage circuit that outputs a speed voltage corresponding to the rotational speed and the temperature based on a speed signal corresponding to the rotational speed of the motor and a temperature signal corresponding to the temperature;
A comparison circuit that compares a reference voltage corresponding to a target rotational speed of the motor and the speed voltage;
A drive circuit for driving the motor to match the voltage level of the speed voltage with the voltage level of the reference voltage based on the comparison result of the comparison circuit;
A motor speed control circuit comprising: The speed voltage circuit includes:
Outputting the speed voltage according to the product of the rotational speed and the temperature based on the speed signal and the temperature signal;
The motor speed control circuit according to claim 1. The speed signal is
It is a pulse signal whose cycle changes according to the rotation speed of the motor,
The speed voltage circuit includes:
A temperature current generation circuit for generating a temperature current according to the temperature signal;
A speed voltage output circuit that outputs the speed voltage according to a product of the period of the pulse signal and a current amount of the temperature current;
The motor speed control circuit according to claim 2, comprising: The speed voltage is
The voltage according to the charging voltage of the capacitor to which the temperature current is supplied,
The speed voltage output circuit includes:
A discharge circuit that discharges the capacitor at intervals according to the period so that the charging voltage is a voltage corresponding to a product of the period of the pulse signal and the amount of the current of the temperature current; The motor speed control circuit according to claim 3. The temperature signal is
A voltage signal generated in a thermistor whose resistance value changes according to the temperature,
The temperature / current generation circuit includes:
A temperature voltage output circuit for outputting a temperature voltage corresponding to the resistance value;
A transistor that outputs the temperature current when the temperature voltage is applied to a control electrode;
5. The motor speed control circuit according to claim 3, further comprising:

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