Fan rotary speed controlling device

This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 099138290 filed in Taiwan, Republic of China on Nov. 8, 2010, the entire contents of which are hereby incorporated by reference.

1. Field of Invention

The present invention relates to a fan rotary speed controlling device and, in particular, to a fan rotary speed controlling device of a brushless DC fan.

2. Related Art

Regarding to the driving mechanism of the motor of a current brushless DC fan, a Hall sensor is involved to determine the positions of magnetic poles of the permanent magnetic rotor after the windings of the stator is powered on. Accordingly, the direction of the current flowing through the windings of the stator is changed to generate the alternative magnetic field, which can push the permanent magnetic rotor to continuously rotate. Currently, the PWM (pulse width modulation) technology is the most popular rotary speed control technology for the fan motor.

As shown in FIG. 1 , a conventional fan rotary speed controlling device 1 is applied to control the rotary speed of a motor 7 . The fan rotary speed controlling device 1 includes a rotary-speed voltage conversion circuit 11 , a control circuit 12 , a pulse width modulation (PWM) circuit 13 , and a switching circuit 14 . The rotary-speed voltage conversion circuit 11 receives a rotary-speed signal S 1 , which represents the rotary speed of the motor 7 while operating. Then, the rotary-speed voltage conversion circuit 11 converts the rotary-speed signal S 1 into a voltage signal S 2 , which is then transmitted to the control circuit 12 . The control circuit 12 , which includes a PID (Proportion-Integral-Differential) controller, receives the voltage signal S 2 and a target voltage signal S 3 , and compares the voltage signal S 2 with the target voltage signal S 3 to output a signal S 4 . The PWM circuit 13 generates a PWM signal S 6 according to the signal S 4 and a fundamental frequency signal S 5 . The switching circuit 14 turns on/off a plurality of switch elements depending on the PWM signal S 6 , so that it can output a control signal S 7 to control the rotary speed of the motor 7 .

The conventional constant-rotary-speed controlling method for motors, such as the above-mentioned PID control or programmable logic control (PLC), can achieve the desired constant-rotary-speed control for motors. However, these conventional methods can not precisely control the rotary speed of the motor, and have the problems of difficult adjustment and high cost.

In view of the foregoing subject, an objective of the present invention is to provide a fan rotary speed controlling device that can enhance the stability and preciseness of the rotary speed.

To achieve the above objective, the present invention discloses a fan rotary speed controlling device including a first signal generating circuit, a second signal generating circuit, a pulse width modulation (PWM) circuit and a switching circuit. The first signal generating circuit receives a real frequency signal and a target frequency signal, and generates a first signal according to the real frequency signal and the target frequency signal. The second signal generating circuit is electrically connected with the first signal generating circuit and generates a second signal according to the first signal. The PWM circuit is electrically connected with the second signal generating circuit and generates a PWM signal according to the second signal. The switching circuit is electrically connected with the PWM circuit and outputs a control signal to control the rotary speed of a motor.

In one embodiment of the present invention, the second signal generating circuit includes a filter for receiving the first signal and filtering the first signal to generate the second signal, which is a DC signal.

In one embodiment of the present invention, the switching circuit comprises a bridge circuit.

In one embodiment of the present invention, the fan rotary speed controlling device further includes an integrated circuit electrically connected with the first signal generating circuit and the switching circuit.

In one embodiment of the present invention, the integrated circuit includes a signal converter for receiving an external PWM signal and generating the target frequency signal according to the external PWM signal.

In one embodiment of the present invention, the integrated circuit includes an oscillator for outputting a square wave signal.

In one embodiment of the present invention, the fan rotary speed controlling device further includes a waveform converting circuit electrically connected with the integrated circuit and the PWM circuit. The waveform converting circuit receives the square wave signal and outputs a third signal to the PWM circuit according to the square wave signal.

As mentioned above, in the fan rotary speed controlling device of the present invention, the first signal generating circuit receives the real frequency signal of an operation motor and a target frequency signal, and generates the first signal according to the real frequency signal and the target frequency signal, the second signal generating circuit generates the second signal according to the first signal, the PWM circuit generates the PWM signal according to the second signal and the fundamental frequency signal, and the switching circuit controls the bridge circuit according to the PWM signal and outputs the control signal depending on ON/OFF states of the switch elements of the bridge circuit so as to control the rotary speed of the motor. Consequently, the fan rotary speed controlling device of the present invention can keep adjusting the rotary speed of the motor, thereby enhancing the preciseness and stability of the motor rotary speed.

The present invention will become more fully understood from the subsequent detailed description and accompanying drawings, which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is a schematic diagram of a conventional fan rotary speed controlling device;

FIG. 2 is a schematic diagram of a fan rotary speed controlling device according to a first embodiment of the present invention;

FIG. 3 is a schematic diagram of a fan rotary speed controlling device according to a second embodiment of the present invention; and

FIG. 4 is a schematic diagram of a fan rotary speed controlling device according to a third embodiment of the present invention.

The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements.

With reference to FIG. 2 , a fan rotary speed controlling device 2 according to a first embodiment of the invention is applied to control the rotary speed of a motor 7 . In this embodiment, the fan rotary speed controlling device 2 is used in a brushless DC fan. The fan rotary speed controlling device 2 includes a first signal generating circuit 21 , a second signal generating circuit 22 , a pulse width modulation (PWM) circuit 23 , and a switching circuit 24 . In order to efficiently enhance the preciseness and stability of the rotary speed of the motor 7 , the fan rotary speed controlling device 2 is designed based on the concept of phase locked loop (PLL).

In addition, the fan rotary speed controlling device 2 further includes a driving circuit 30 and a rotary-speed detecting circuit 31 . The rotary-speed detecting circuit 31 includes a rotary-speed detecting element for detecting the rotary speed of the operating motor 7 . The rotary-speed detecting circuit 31 can further convert the detected rotary speed into an operating frequency and thus generate a real frequency signal S 11 . Then, the real frequency signal S 11 is transmitted to the first signal generating circuit 21 and the driving circuit 30 . In this embodiment, the rotary-speed detecting element can be a Hall sensor or an opto-coupler.

The first signal generating circuit 21 receives the real frequency signal S 11 and a target frequency signal S 12 . In this embodiment, the target frequency signal S 12 is generated by a target frequency generating circuit 25 and output to the first signal generating circuit 21 . The target frequency signal S 12 represents the frequency corresponding to the desired rotary speed of the motor 7 . Then, the first signal generating circuit 21 generates a first signal S 13 according to the relative error between the real frequency signal S 11 and the target frequency signal S 12 .

The second signal generating circuit 22 is electrically connected with the first signal generating circuit 21 and includes a filter. The filter receives the first signal S 13 and filters it to generate a second signal S 14 , which is a direct current (DC) signal.

In addition, the fan rotary speed controlling device 2 further includes a fundamental frequency generating circuit 26 , which generates a fundamental frequency signal S 15 . In this embodiment, the fundamental frequency signal S 15 is a triangle wave.

The PWM circuit 23 is electrically connected with the second signal generating circuit 22 and the fundamental frequency generating circuit 26 . In this embodiment, the PWM circuit 23 generates a PWM signal S 16 according to the second signal S 14 and the fundamental frequency signal S 15 , and then outputs the PWM signal S 16 to the switching circuit 24 .

The switching circuit 24 is electrically connected with the PWM circuit 23 . The switching circuit 24 includes a bridge circuit such as a single-phase full-bridge circuit, single-phase half-bridge circuit or three-phase full-bridge circuit. In practice, the switching circuit 24 controls the ON/OFF states of the switch elements of the bridge circuit according to the PWM signal S 16 , and then outputs a control signal S 17 depending on the ON/OFF states of the switch elements and the signal 11 ′ converted from the real frequency signal 11 by the driving circuit 30 so as to control the rotary speed of the motor 7 .

Regarding to a PLL, it is composed of a phase/frequency detector (PFD), a loop filter and a voltage control oscillator (VCO), all of which are connected with each other to form a closed loop. In this embodiment, the first signal generating circuit 21 is equivalent to a PFD, the second signal generating circuit 22 is equivalent to a loop filter, and the PWM circuit 23 , the switching circuit 24 and the motor 7 are together to be equivalent to a VCO.

The first signal generating circuit 21 receives the target frequency signal S 12 and takes the real frequency signal S 11 outputted from the motor 7 as a feedback signal. Furthermore, the first signal generating circuit 21 can generate the first signal S 13 according to the error between the target frequency signal S 12 and the real frequency signal S 11 , and then outputs the first signal S 13 to the second signal generating circuit 22 . Then, the filter of the second signal generating circuit 22 filters the first signal S 13 to generate the second signal S 14 , which is a DC signal, and the second signal generating circuit 22 outputs the second signal S 14 to the PWM circuit 23 . The PWM circuit 23 outputs the PWM signal S 16 to the switching circuit 24 after comparing the second signal S 14 with the fundamental frequency signal 15 . Accordingly, the switching circuit 24 can control the rotary speed of the motor 7 . By repeating the above procedures, the rotary speed of the motor 7 can be adjusted until that the real frequency signal S 11 is equal to the target frequency signal S 12 . When the real frequency signal S 11 is equal to the target frequency signal S 12 , the first signal S 13 outputted by the first signal generating circuit 21 is fixed so that the rotary speed of the motor 7 can be kept constant.

The above description discloses the fundamental aspect of the fan rotary speed controlling device of the invention, and the further modified aspects thereof will be illustrated hereinafter with reference to the following two embodiments.

Referring to FIG. 3 , a fan rotary speed controlling device 3 according to a second embodiment of the invention includes a first signal generating circuit 21 , a second signal generating circuit 22 , a PWM circuit 23 , a switching circuit 24 and a rotary-speed detecting circuit 31 . Compared with the above-described first embodiment, the fan rotary speed controlling device 3 of this embodiment further includes an integrated circuit 27 and a waveform converting circuit 28 . The integrated circuit 27 includes a logic controller 271 with programmable software, an oscillator 272 , and a signal converter 273 . The integrated circuit can be a microcontroller, a microprocessor, a programmable gate array (PGA), or an application-specific integrated circuit (ASIC) component.

The rotary-speed detecting circuit converts the rotary speed of the motor 7 into an operating frequency and thus generates a real frequency signal S 21 . Then, the real frequency signal S 21 is transmitted to the first signal generating circuit 21 and the logic controller 271 .

The logic controller 271 is electrically connected with the switching circuit 24 and converts the real frequency signal S 21 to a signal S 21 ′ to be transmitted to the switching circuit 24 . The oscillator 272 outputs a square wave signal S 22 to the waveform converting circuit 28 . The signal converter 273 receives an external PWM signal S 23 and converts the external PWM signal S 23 into a target frequency signal S 24 according to the duty cycle of the external PWM signal S 23 .

The first signal generating circuit 21 receives the real frequency signal S 21 and the target frequency signal S 24 , and then generates a first signal S 25 according to the real frequency signal S 21 and the target frequency signal S 24 .

The second signal generating circuit 22 is electrically connected with the first signal generating circuit 21 and includes a filter. The filter receives the first signal S 25 and filters it to generate a second signal S 26 , which is a DC signal.

The waveform converting circuit 28 electrically connected with the oscillator 272 receives the square wave signal S 22 and converts it into a signal S 27 which is a triangle wave signal.

The PWM circuit 23 is electrically connected with the second signal generating circuit 22 and the waveform converting circuit 28 . In this embodiment, the PWM circuit 23 generates a PWM signal S 28 according to the second signal S 26 and the signal S 27 , and then outputs the PWM signal S 28 to the switching circuit 24 .

The switching circuit 24 is electrically connected with the PWM circuit 23 , and it includes a bridge circuit such as a single-phase full-bridge circuit, single-phase half-bridge circuit or three-phase full-bridge circuit. In this embodiment, the switching circuit 24 controls the ON/OFF states of the switch elements of the bridge circuit according to the PWM signal S 28 , and then outputs a control signal S 29 depending on the ON/OFF states of the switch elements and the signal S 21 ′ so as to control the rotary speed of the motor 7 .

Referring to FIG. 4 , a fan rotary speed controlling device 4 according to a third embodiment of the invention includes a first signal generating circuit 21 , a second signal generating circuit 22 , a PWM circuit 23 , a switching circuit 24 , a target frequency generating circuit 25 , and a rotary-speed detecting circuit 31 . Compared with the above-described first embodiment, the fan rotary speed controlling device 4 of this embodiment further includes an integrated circuit 27 and a waveform converting circuit 28 . The integrated circuit 27 includes a logic controller 271 with programmable software and an oscillator 272 .

The rotary-speed detecting circuit 31 converts the rotary speed of the motor 7 into an operating frequency and thus generates a real frequency signal S 31 . Then, the real frequency signal S 31 is transmitted to the first signal generating circuit 21 and the logic controller 271 .

The logic controller 271 is electrically connected with the switching circuit 24 and converts the real frequency signal S 31 to a signal 31 ′ to be transmitted to the switching circuit 24 . The oscillator 272 outputs a square wave signal S 32 to the waveform converting circuit 28 .

The target frequency generating circuit 25 generates a target frequency signal S 33 , which indicates the desired rotary speed of the motor 7 , and then outputs the target frequency signal S 33 to the first signal generating circuit 21 .

The first signal generating circuit 21 receives the real frequency signal S 31 and the target frequency signal S 33 , and then generates a first signal S 34 according to the real frequency signal S 31 and the target frequency signal S 33 .

The second signal generating circuit 22 is electrically connected with the first signal generating circuit 21 and includes a filter. The filter receives the first signal S 34 and filters it to generate a second signal S 35 which is a DC signal.

The waveform converting circuit 28 electrically connected with the oscillator 272 receives the square wave signal S 32 and converts it into a signal S 36 which is a triangle wave signal.

The PWM circuit 23 is electrically connected with the second signal generating circuit 22 and the waveform converting circuit 28 . In this embodiment, the PWM circuit 23 generates a PWM signal S 37 according to the second signal S 35 and the signal S 36 , and then outputs the PWM signal S 37 to the switching circuit 24 .

The switching circuit 24 is electrically connected with the PWM circuit 23 , and includes a bridge circuit such as a single-phase full-bridge circuit, single-phase half-bridge circuit or three-phase full-bridge circuit. In this embodiment, the switching circuit 24 controls the ON/OFF states of the switch elements of the bridge circuit according to the PWM signal S 37 , and then outputs a control signal S 38 depending on the ON/OFF states of the switch elements and the signal S 31 ′ converted from the real frequency signal S 31 by the logic controller 271 so as to control the rotary speed of the motor 7 .

To sum up, in the fan rotary speed controlling device of the present invention, the first signal generating circuit receives the real frequency signal of an operation motor and a target frequency signal, and generates the first signal according to the real frequency signal and the target frequency signal, the second signal generating circuit generates the second signal according to the first signal, the PWM circuit generates the PWM signal according to the second signal and the fundamental frequency signal, and the switching circuit controls the bridge circuit according to the PWM signal and outputs the control signal depending on ON/OFF states of the switch elements of the bridge circuit so as to control the rotary speed of the motor. Consequently, the fan rotary speed controlling device of the present invention can keep adjusting the rotary speed of the motor, thereby enhancing the preciseness and stability of the motor rotary speed.

Although the present invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the present invention.