JP2884584B2 - DC fan - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A. Industrial application fields B. Summary of the invention C. Prior art D. Problems to be solved by the invention E. Means to solve the problems F. Function G. Embodiment G _1. First Embodiment construction and operation (FIG. 1) G _2. configuration and operation of the second embodiment (FIG. 2, FIG. 3 (a), (b), FIG. 4, FIG. 5) G _3. third embodiment Example Configuration and Operation (FIGS. 6 and 7) H. Effects of the Invention A. Industrial Application Field The present invention relates to a DC fan with improved cooling efficiency and versatility.

B. Summary of the Invention The present invention relates to a DC fan using a DC fan motor, wherein the rotation speed of the DC fan motor is speed-controlled at a predetermined specified speed by a speed servo circuit, and the specified speed of the DC fan motor is set to a temperature of a cooling target. Increase / decrease by the temperature servo circuit based on the detection, suppress the decrease in the air volume with the speed servo against the increase / decrease of the load, etc. And at the same time, the same motor specifications can be used for various applications.

C. Prior Art Conventionally, a fan has been used for exhaust heat cooling of a set of various devices. The conventional fan is an AC fan using an AC motor, and a DC fan using a DC motor is also used in some cases in order to prevent the fan from being affected by the specifications of the commercial power supply in the place of use. For any of the fans, the rated speed is 1500, 2000, 2500, 3000,
By using motors having different rotation speed-torque characteristics such as 3500 rpm, a plurality of types of fans have been prepared. Among DC fans, those that detect a specific temperature with a temperature sensor and perform high-speed rotation at a temperature equal to or higher than that temperature to adjust the air volume in two stages are also commercially available.

D. Problems to be Solved by the Invention However, in the fan in the above-mentioned conventional technology,
As shown in the characteristic diagram of the fan of the conventional example in FIG. 8, since the fan motor is used at the point corresponding to the used load on the rotation speed N-torque T characteristic of the fan motor, there are the following problems. .

(1) If the load increases with an increase in dust or the like or the static pressure on the set structure, the number of revolutions N decreases, so that the air volume decreases and the heat generation of the set increases.

(2) Conversely, when the load decreases, the number of rotations increases and the air volume increases, so that noise increases.

(3) Variation of supply voltage to fan motor and number of rotations N
-The air volume is not constant because the rotation speed fluctuates due to variations in the torque T characteristic.

(4) When actually selecting a fan, in consideration of the variation in (3), an increase in the set temperature, and the use environment, use a fan more than necessary with a sufficient margin, or use a low ambient temperature or a low set temperature. In some cases, as in the case of high speed, the number of revolutions is increased and the air flow is increased, so that noise is increased.

(5) Therefore, if a specific temperature is detected by the temperature sensor and the air temperature is adjusted in two stages by rotating at a high speed only at a certain temperature or higher, the noise in (4) when the environmental temperature or the set temperature is low is eliminated. However, the change in noise at the switching point is also a matter of concern for the user.

(6) In any case, since the air volume cannot be continuously changed according to the temperature rise of the set, the cooling efficiency is poor.

(7) The cooling capacity is fixed for each fan, there is no versatility, and different fans must be selected according to the application.

The present invention has been made in order to solve the above problems, while increasing the cooling efficiency and reducing noise,
It is an object of the present invention to provide a DC fan capable of coping with various uses with different amounts of heat exhausted by the same motor.

E. Means for Solving the Problems The configuration of the DC fan of the present invention for achieving the above object is a DC fan motor that rotates the blades, and detects a speed of the DC fan motor and outputs a predetermined designated speed signal. A speed servo circuit for comparing and controlling the speed to the specified speed, and a temperature servo for detecting the temperature of the cooling object and increasing or decreasing the specified speed in accordance with the increase or decrease of the temperature, having means for freely setting the specified speed. And a circuit.

F. Function The present invention controls the speed of the DC fan motor to a specified speed by a speed servo circuit, thereby suppressing a decrease in the air flow against an increase in load, while suppressing a variation in motor characteristics, supply voltage, and the like. While eliminating variations in air volume,
By changing the designated speed, it is possible to meet the required performance of various applications. Further, the specified speed is continuously increased or decreased by the temperature servo circuit in accordance with the detected temperature of the object to be cooled, so that cooling efficiency is increased and noise is reduced.

G. Examples Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

G _1. Configuration and Operation of First Embodiment (FIG. 1) FIG. 1 is a circuit diagram showing a first embodiment of the present invention. 1 is, for example, a DC fan motor that rotates a blade 11 that generates an axial flow, 2 is a driver that drives the DC fan motor 1, and 3 is a motor that detects the speed of the DC fan motor 1 and compares it with a designated speed signal _Vref. A speed servo circuit 4 for controlling the speed to a designated speed is a temperature servo circuit for detecting the temperature of a cooling target (such as a set) and continuously increasing or decreasing the designated speed signal _Vref according to the increase or decrease of the temperature. Driver, speed servo circuit 3, temperature servo circuit 4, etc., excluding external elements
It is preferable to use an IC (integrated circuit) 5.

The speed servo circuit 3 includes a speed detection unit 31 of the DC fan motor 1 and a current exchange unit that converts the detection signal into a current signal.
32, a capacitor C ₁ and resistor R ₁ to be detected velocity signal V _M a current signal to the pulsating by charge and discharge, the detected speed signal
Comparing the V _M and the specified velocity signal V _ref an operational amplifier 33 for outputting the deviation signal to the driver 2. Capacitor C ₁ and resistor R ₁ is connected with an external parallel, one end the current converter
It is connected to 32 and connected to one input (non-inverting input terminal +) of an operational amplifier 33, and the other end is connected to ground.

The temperature servo circuit 4 includes a voltage dividing circuit of _two resistors R ₂ and R ₃ for dividing the stabilized voltage V _reg to generate a reference voltage V ₁ , and a thermistor R _th attached to a set or the like to be cooled. A voltage dividing circuit that _{divides the} stabilizing voltage V _reg with the connection resistor R ₄ to generate a detected temperature signal V _th for a cooling target, compares the reference voltage V ₁ with the detected temperature signal V _th, and compares the difference. And a temperature-sensitive amplifier 41 that amplifies and creates a command speed signal _Vref . An operational amplifier can be used as the temperature-sensitive amplifier 41. Reference voltages V ₁ is connected to the non-inverting input terminal of the temperature-sensitive amplifier 41 +, temperature detection signal V _th inverting input terminal of the temperature-sensitive amplifier 41 -
Connect to The output _Vref of the temperature-sensitive amplifier 41 is connected to the inverting input terminal of the temperature-sensitive amplifier 41 via an external feedback resistor _Rf . The command speed signal _Vref is connected to the inverting input terminal-of the operational amplifier 33 of the speed servo circuit 3.

In the configuration of the first embodiment described above, the resistance value of the thermistor _Rth changes continuously depending on the temperature of the object to be cooled, and the detected temperature signal _Vth increases and decreases continuously as the temperature increases and decreases. The temperature-sensitive amplifier 41 _compares the detected temperature signal _Vth with the reference voltage _Vth.
In comparison with ₁ , the designated speed signal _Vref is increased or decreased continuously according to the difference, for example, if the temperature rises, the designated speed increases. Velocity servo circuit 3, a speed signal relative to the designated speed signal V _ref, the operational amplifier 33, so that the actual detected speed signal V _M of the DC fan motor 1 is equal to the specified speed signal V _ref, the driver 2 , The feedback control is performed. Therefore, even if the static pressure increases and the load increases, the rotation speed of the DC fan motor 1 is kept constant by the servo circuit 3 without decreasing, and the decrease in the air volume is suppressed. On the other hand, even if the load decreases or becomes lighter than expected, the rotation speed of the DC fan motor 1 is kept constant by the servo circuit 3 without increasing, and an excessive air volume is generated. Noise does not increase. Similarly, the rotation speed is constant without being affected by variations in the NT characteristics of the DC fan motor 1 and variations in the supply voltage thereof, and there is no variation in the air volume. When the ambient temperature or the set temperature is low, the DC fan motor 1 is controlled by the temperature servo circuit 4.
When the temperature is high, the rotational speed is continuously increased in accordance with the temperature to increase the cooling efficiency. At this time, since the change in speed is stepless, a sudden change in the annoying noise is not felt.

In the servo control, the slope and the absolute values of temperature versus torque characteristic, the value of the temperature coefficient and the feedback resistor R _f of the thermistor R _th, can be freely set by the resistance ratio of the thermistor R _th and the external resistor R _4. For this reason, various rotation speeds can be obtained at normal temperature and arbitrary temperature with the same motor specification, so that it is not necessary to provide an unnecessary fan or select a fan having a different specification for each application.

G _2. Configuration and operation of the second embodiment (FIGS. 2, 3 (a), (b), FIGS. 4, 5) FIG. 2 shows a second embodiment of the present invention. It is a circuit block diagram. This embodiment is a more practical configuration of the first embodiment, and shows an example in which an OTM (one-sensor two-phase motor) is used as a DC fan motor. Also in this embodiment, IC5 is used except for external elements. 12 OTM the A-phase coil, 13 is the same B-phase coil of the OTM, the common side is connected to the DC power supply terminal V _cc of the external terminal board 6, L _a terminal of the other end in the case of A-phase coil 12 IC 5 , IC5 for B phase coil 13
To the _Lb terminal. L _a, L _b terminals are connected to the driver.

The driver includes a Hall effect element 21, a Hall amplifier 22 that amplifies the Hall voltage to generate a polarity detection signal, a switching / output driver 23, and an excitation current of each phase coil 12, 13 based on an output of the switching / output driver 23. , And two power transistors Q ₁ , Q _2, etc. Connected to the collector L _a terminal of the power transistor Q _1, the power transistor
The collector of Q ₂ is connected to L _b terminal, each emitter is connected to the ground terminal GND of the IC 5, the switching-each base individually
Connect to output driver 23. The Hall effect element 21 is connected between the DC power supply terminal _Vcc of the external terminal plate 6 and the ground terminal GND.
Connected via an R _11, it detects the polarity of the rotor magnet of the below-described OTM as Hall voltage, the Hall voltage IC5
H _a, is inputted through H _b terminals to the differential of the Hall amplifier 22. The switching / output driver 23 alternately outputs the respective base currents of the power transistors Q ₁ and Q ₂ based on the polarity detection signal of the Hall amplifier 22 to switch the excitation timing of the A-phase coil 12 and the B-phase coil 13. Further, the switching / output driver 23 controls the excitation current by increasing or decreasing the base current according to the output of the speed servo circuit 3. Switch C ₁₁
This is a capacitor for frequency compensation of the output driver 23.

Velocity servo circuit 3 has the same configuration as the first embodiment, in this embodiment, detects the L _a, the counter electromotive voltage proportional to the rotational speed generated from the L _b terminals to the coil 12, which replace the current, creates a detected speed signal by charging and discharging by the capacitor C ₁ of the external and the resistor R _1, the switching-designation velocity signal from the temperature sensing amplifier 41 of the temperature servo circuit as a reference speed signal Speed control is applied to the output driver 23.

Temperature servo circuit includes a temperature sensitive amplifier 41 in the present embodiment, the inverting input terminal - a feedback resistor R _r of external reference voltage source E and the temperature-sensitive amplifier 41 to provide a reference voltages V _1, at a temperature sensing element And a thermistor _Rth having a certain positive characteristic or negative characteristic.
The temperature detection element thermistor _Rth is preferably installed in the set, particularly in a place where the temperature rises the most or where cooling is desired best. One end of the thermistor R _th is a temperature sensitive amplifier 41
To the non-inverting input terminal +, and the other end to the ground terminal
Connect to GND. The feedback resistor _Rf is connected between the output of the temperature sensitive amplifier 41 and the non-inverting input terminal +.

Reference numeral 51 denotes an automatic return control circuit, and reference numeral 52 denotes a heat cutoff circuit. Both detect a dangerous state and instruct the switching / output driver 23 to stop excitation of the coils 12 and 13. Also,
Both circuits 51 and 52 have an automatic return function of automatically canceling the excitation stop after leaving the danger state. Automatic return control circuit 51, L _a, a counter electromotive voltage generated from the L _b terminal of each phase coil 12, 13 of the motor as compared with the DC power supply V _cc, to create a pulse-like rotation detection signal, the resistor R ₁₂ And capacitor C
_A threshold value is set by a charge / discharge circuit including _{12 and the} like, and the rotation state of the motor is determined by determining the level of the rotation detection signal.If the rotation is abnormally low or stopped, the excitation is stopped. specify. At the same time, the transistor Q ₃ which connects the emitter to ground is turned on or off, and outputs from the RD terminal of the external terminal board 6 the alarm signals for the system down to the set. Alarm signal from the collector of the transistor Q _3, a power supply V _cc by the resistors R ₁₃
And output at low level or high level. In the normal state, the opposite level of the alarm is output. The thermal cutoff circuit 52 detects an abnormally high shunting temperature, instructs excitation stop, and releases the excitation stop when it returns to normal.

3 (a) and 3 (b) are configuration diagrams of a DC fan motor (OTM) in a second embodiment, (a) is a configuration diagram of a stator, and (b) is a configuration diagram of a rotor magnet.
The stator 14 (a) and the rotor magnet 15 (b) the centers O _S and O _R is arranged to face to match. The rotor magnet 15 is radially divided into six equal parts, and N-poles and S-poles are alternately magnetized in the divided parts 15a. In the peripheral portion of the divided portion 15a, a magnetic pole opposite to the above-described magnetization is formed in a small portion 15b of every other adjacent magnetic pole portion. On the other hand, on the side of the stator 14, two A-phase coils 12, 12 and two B-phase coils 13, 13 are alternately arranged at the same pitch angle as the divided portion 15a, and the Hall effect element 21 is disposed at the magnetic pole of the divided portion 15a. only disposed in the portion for detecting (center O _S closer). here,
When the A-phase coils 12 and 12 and the B-phase coils 13 and 13 are alternately excited, a rotating torque acts in a fixed direction by the action of the opposite magnetic pole of the small portion 15b, and the rotor magnet 15 can be rotated.

In the second embodiment having the above configuration, the thermistor R _th
Is changed according to the set temperature, the designated speed signal of the temperature-sensitive amplifier 41 changes according to the change amount. At this time, for example, if the temperature rises, the designated speed signal is changed such that the designated speed increases. Speed servo circuit 3
Switches the feedback control to the rotation speed instructed by the specified speed signal, and applies the feedback control to the control driver 23.The switching and control driver 23 controls the base currents of the power transistors Q ₁ and Q ₂ according to the instruction, The rotation speed is controlled to the specified speed by controlling the excitation current. Therefore, the second embodiment operates similarly to the first embodiment and has the same operation and effect.

4 and 5 are characteristic diagrams of a fan showing the effect of the second embodiment. FIG. 4 is a diagram showing a DC (direct current) 12 V, rated speed.
The characteristic diagram of the air flow Q vs. the static pressure P and the number of rotations (rotational speed) N comparing the case where the speed servo of this embodiment is applied (1) and the case where the speed servo is not applied using a 4000 rpm DC fan motor is shown. FIG. 5 shows a characteristic diagram of the temperature T versus the rotation speed N when the temperature servo is applied (1) and when the temperature servo is not applied (2) according to the present embodiment. In FIG. 4, when the speed servo is applied (1), the rotation speed is substantially constant with respect to the change in the air flow, and the decrease in the air flow is suppressed for the same static pressure P. It can be seen that is improved. In FIG. 5, when the temperature servo is applied (1), the temperature becomes
When the temperature rises from 20 ° C to 40 ° C, about 450 continuously from 3000rpm
The rotation speed can be increased to 0 rpm, and conversely, when the temperature decreases to 0 ° C., the rotation speed can be continuously reduced from 3000 rpm to 1600 rpm, and the cooling efficiency can be increased as compared with the case (2) without the temperature servo.

G _3. Configuration and Operation of Third Embodiment (FIGS. 6 and 7) FIG. 6 is a circuit diagram showing a third embodiment of the present invention. In the present embodiment, the temperature servo circuit is a current comparison type, which simplifies the circuit, and realizes miniaturization in the case of an IC. 1 is a DC fan motor for rotating a blade 11 for generating an axial flow, for example, 2 is a driver for driving the DC fan motor 1, and 3 is a speed for detecting the speed of the DC fan motor 1 based on a back electromotive force of a coil. Speed servo circuit that compares the signal with the specified speed _Vref and controls the speed to the specified speed.
Is a temperature servo circuit for detecting the temperature of a cooling target (such as a set) and sucking the detected speed signal in accordance with the increase or decrease of the temperature to continuously increase or decrease the designated speed relatively. driver
2, the speed servo circuit 3, the temperature servo circuit 4, etc. are 1C (integrated circuit) 5 excluding external elements.

The speed servo circuit 3 includes a speed detector 31 of the DC fan motor 1 and a current converter that converts the detection signal into a current signal.
32 and charge / discharge of this pulsating current signal and the detected speed signal
A capacitor C ₁ to V _M and the resistor R _1, the detection speed signal V _M
And an operational amplifier 35 that compares the specified speed voltage _Vref supplied from the constant voltage source 34 and outputs a deviation signal to the driver 2. Capacitor C ₁ and resistor R ₁ is externally connected in parallel, one end is connected to one input of the operational amplifier 35 is connected to the current exchange section 32 (non-inverted input terminal +), the other end is connected to ground .

Temperature servo circuit 4, the reference resistor R _ref and the thermistor R _th external that respectively connect one end to the ground, stabilized voltage V _reg resistor R ₂₁ and the divided potential with R ₂₂ V _O the reference resistor R _ref to connection (a) to the circuit 42 for supplying the terminal and the thermistor R _th of connecting (B) reference current i ₁ and the detected temperature current i ₂ is given to each of the terminals, the reference resistance
The difference current i ₃ between the reference current i ₁ flowing in R _ref and the detected temperature current i ₂ flowing in the thermistor R _th (= i ₁ −i ₂ , where R _ref <R _th,
i ₁ > i ₂ ) and the difference current i ₃
Is multiplied by, for example, N times, and a current mirror circuit 44 for drawing a current from the detected speed signal in the speed servo circuit 3 described above. Circuit 42 has a pnp transistor Tr ₁ and an npn transistor T
r ₂ and Tr ₃ . The emitter of the transistor Tr ₁ is a resistor R ₂₃
Connected to the circuit power supply V _cc through, its collector connected to ground, and its base connected to the voltage V _o. The bases of the transistors Tr ₂ and Tr ₃ are connected to the transistor Tr ₁ described above.
Connect to the emitter, the emitter of the transistor Tr ₂ is to (A) terminal, the emitter of the transistor Tr ₃ is connected to the (B) terminal. Circuit 43 is a pnp transistor Tr ₄ , T
It consists of a circuit of r ₅ and Tr ₆ . The emitter of the transistor Tr ₄ is connected to the circuit power supply V _cc through a resistor R _24, its collector connected to the collector of the above transistor Tr _2. The emitter of the transistor Tr ₅ is connected via a resistor R ₂₅ to the circuit power supply V _cc, and its collector is connected to the collector of the transistor Tr ₃ of the above. The bases of the transistors Tr ₄ and Tr ₅ are both connected to the collector of the transistor Tr ₂ . The emitter of the transistor Tr ₆ is connected to the collector of the above transistor Tr _5, the base is connected to the collector of the transistor Tr _1. Current mirror circuit 44 is comprised of a circuit of an npn transistor Tr _7, Tr _8. Collector and base of the transistor Tr ₇ is connected to the collector of the transistor Tr _6, the emitter is connected to ground. Base of the transistor Tr ₈ is connected to the collector of the transistor Tr _7, emitter to ground, collector connected to the input point of the operational amplifier 35 of the detected speed signal from the current exchange section 32 of the velocity servo circuit 3 (C). Here, the emitter area of the transistor Tr ₈ is N times the transistor Tr _7. Thereby, the transistor T
The collector of r ₇ - emitter the difference current i ₃ flows into, i ₄ which transistors Tr ₈ is amplified N times (C) point
(= N · i ₃ ).

In the third embodiment having the above configuration, the currents i ₁ , i ₂ and i ₃ of the temperature servo circuit 4 have the following values.

i ₁ = V _o / R _ref i ₂ = V _o / R _th i ₃ = i ₁ −i ₂ Here, if the temperature at the place where the thermistor R _th is attached rises, the thermistor R _th according to the temperature Increases, and the detected temperature current i ₂ decreases. Then, the difference current i ₃ is the difference between the reference current i ₁ and the detected temperature current i ₂ is increased. If it reverses the temperature falls, the differential current i ₃ is moved in the direction to decrease. This difference current i ₃ is calculated by the current mirror circuit of the next stage.
44 is amplified N times, draw current or detection speed current flows into the resistor R ₁ in the N times larger current i ₄ = N · i ₃ only velocity servo circuit 3. As a result, the designated speed indicated by the designated speed voltage _Vref relatively increases or decreases. Therefore, "temperature rise → R _th → i ₂ small → i ₃ → large → i ₄ large → speed increase” or “temperature decrease → R _th small → i ₂ large → i ₃ small → i ₄ small → speed decrease” With such a flow, the temperature servo can be realized as in the first and second embodiments.

FIG. 7 shows the temperature T (° C.) of the fan in the third embodiment.
FIG. 4 is an explanatory diagram of a characteristic of a rotation speed N (rpm). Rotation speed N
The slope △ N / △ T of the temperature characteristic determined in proportion to the temperature coefficient of the thermistor R _th, the absolute value by changing the resistance R ₁ of the external, larger by reducing the resistance value, as shown It can be set freely, for example, it can be made smaller by making it larger. Further, the temperature change, the change amount of the current flowing in the resistor R _1, the reference resistance R is also varied by _ref and the resistance value of the thermistor R _th, specifically to the absolute value of the resistance and temperature coefficient of the thermistor R _th is Therefore, the setting range of the change rate can be widened. Table 1 shows an experimental example. However, the gain of the current mirror circuit 44 is 1, and the thermistor R _th and the reference resistance R _ref are respectively
It is assumed that 100 μA flows at 10 KΩ.

As described above, in the third embodiment, as described in the first embodiment, various rotation speeds can be obtained at normal temperature and arbitrary temperature with the same motor specifications, and a fan more than necessary can be provided, and There is no need to select fans with different specifications.

Further, in the third embodiment, in the temperature servo circuit 4, as in the second embodiment, the number of used pins of the IC is two and the number of external elements is only two, and the temperature servo circuit 4 is different from the first and second embodiments. Since the circuit is simplified and the number of elements is reduced, it is possible to contribute to the space saving of the fan required to be downsized.

Various DC motors other than the OTM can be used as the DC fan motor, and thermistor _Rth can use other temperature detecting elements. In the third embodiment, the circuit on the speed command voltage _Vref side may be directly operated by the temperature servo circuit 4. As described above, the present invention can be applied in various ways according to the gist and can take various embodiments.

H. Effects of the Invention As is clear from the above description, according to the DC fan of the present invention, (1) the rotational speed is almost constant by the speed servo even if the supply voltage to the motor fluctuates. The air volume does not vary.

(2) The rotation speed can be kept substantially constant even if the NT characteristics of the motor vary.

(3) When the set temperature is low, the motor rotates slowly and at an appropriate number of revolutions as the temperature rises, so that the air volume can be obtained and the cooling efficiency is improved.

(4) The number of rotations can be freely set, and various numbers of rotations can be obtained with the same motor specifications.

(5) The number of rotations at room temperature and the number of rotations at an arbitrary temperature can be easily selected.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a first embodiment of the present invention, and FIG.
FIG. 3 is a circuit diagram showing a second embodiment of the present invention, FIGS. 3 (a) and 3 (b) are diagrams showing the configuration of a DC fan motor according to the second embodiment, and FIGS. FIG. 6 is a circuit diagram showing a third embodiment of the present invention, FIG. 7 is an explanatory diagram of the characteristics of the fan of the third embodiment, and FIG. It is a characteristic view of the fan of the conventional example. 1 ... DC fan motor, 3 ... Speed servo circuit, 4 ...
... temperature servo circuit, 31 ... speed detector, 33, 35 ... operational amplifier, 41 ... temperature-sensitive amplifier, 43 ... circuit (means for detecting difference signal), 44 ... current mirror circuit (increase / decrease specified speed) Means), V _ref …… Specified speed signal (specified speed voltage), R
_th ... Thermistor.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-280911 (JP, A) JP-A-56-40489 (JP, U) JP-A-57-165098 (JP, U) (58) Investigation Field (Int.Cl. ⁶ , DB name) H02P 5/00-5/26 H02P 7/00-7/34 H02P 6/02

Claims (2)

(57) [Claims] 1. A DC fan motor for rotating blades, a speed servo circuit for detecting the speed of the DC fan motor, comparing the detected speed with a specified speed signal, and controlling the speed to the specified speed, With means for setting
A DC fan, comprising: a temperature servo circuit that detects a temperature of a cooling target and increases or decreases the specified speed according to the increase or decrease of the temperature. 2. A DC fan according to claim 1, wherein the temperature servo circuit detects a difference signal between a freely settable reference current and the detected temperature current, and designates a speed servo circuit by the difference signal. Means for increasing and decreasing the speed.