# Patent

## Title
Motor driving device

## Abstract

The invention discloses a motor driving device for generating at least one driving signal according to a clock signal corresponding to the output signal of a hall sensor. The motor driving device also controls rotation of a motor via at least one driving signal, wherein the at least one driving signal includes a first driving signal and a second driving signal and the motor driving device controls the rotation of the motor according to the first driving signal and the second driving signal.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 097212148, filed in Taiwan, Republic of China on Jul. 9, 2008, the entire contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a motor driving device, and more particularly to a soft-cut motor driving device for preventing backflow current.
2. Description of the Related Art
As electronic components increase requirement for more and more power, more and more heat has to be accordingly dissipated. Therefore, various heat-dissipation devices have already been developed, with the most popular being motor-controlled fans.
The description of a single-phase motor is discussed hereafter, with reference to FIG. 1 and FIG. 2. FIG. 1 illustrates a schematic diagram of a typical single-phase DC motor driving device. And FIG. 2 is a signal oscillogram of a typical motor driving device. As shown in FIG. 1 and FIG. 2, the typical single-phase DC motor driving device 10 comprises a Hall sensor 12, a detecting device 14, a control circuit 16 and a full-bridge driving circuit 18. Hall sensor 12 is used to detect the rotational position of the motor rotor and generate a first sensing signal SD1 and a second sensing signal SD2. The detecting device 14 is used to generate a clock signal SCLK according to the first sensing signal SD1 and the second sensing signal SD2. The control circuit 16 is used to generate four sets of driving signals A, B, C and D according to the clock signal SCLK. The full-bridge driving circuit 18 comprises a first switch SW1, a second switch SW2, a third switch SW3, a fourth switch SW4 and an inductor L. The full-bridge driving circuit 18 is coupled to a supply voltage VCC. The first switch SW1 and the second switch SW2 are respectively controlled by one of the driving signals A and D which are generated from the control circuit 16, while the third switch SW3 and the fourth switch SW4 are respectively controlled by the driving signal C, D which are generated from the control circuit 16. One end of the inductor L is coupled to the first switch SW1 and the fourth switch SW4 at the point N1, and the other end of the inductor L is coupled to the third switch SW3 and the second SW2 at the point N2. The first switch SW1 and the second switch SW2 are turned on or off in accordance with the third switch SW3 and the fourth switch SW4. Specifically, when the first switch SW1 and the second switch SW2 are turned on and the third switch SW3 and the fourth switch SW4 are turned off, an inductor current IL would flow through the inductor L from the point N1 to the point N2. Alternatively, when the first switch SW1 and the second switch SW3 are turned off and the third switch SW3 and the fourth switch SW4 are turn on, the inductor current IL on the inductor L would flow from the point N2 to the point N1. Therefore, the rotational direction and speed of the motor may be controlled by appropriately changing the quantity and the direction of the driving current of the inductor L. The first switch SW1, the second switch SW2, the third switch SW3 and the fourth switch SW4 may be respectively composed of transistors.
When the motor rapidly switches the switches SW1 ̃SW4 of the full-bridge circuit 18, a high-frequency voltage pulse may occur, which increases rotating motor noise. Moreover, during the switching process, if the current through the motor is unable to be released in a short time, the inductor current IL would flow back to the supply voltage VCC and generate a voltage surge to cause the motor driving device 10 broken.
FIG. 2 is a schematic diagram illustrating a signal generated by subtracting the second sensing signal SD2 from the first sensing signal SD1, the clock signal SCLK, two driving signals SC1 and SC2 flowing through the point N1 and N2, respectively, and the inductor current IL. When the first sensing signal SD1 generated by the Hall sensor 12 is larger than the second sensing signal SD2, the signal (SD1-SD2) from the first sensing signal SD1 subtracting the second signal SD2 is positive. Since the detecting device 14 is a hysteresis comparator, there exists a time de-glitch, as label t (de-glitch) in FIG. 2 shows, when comparing the clock signal SCLK generated by the detecting device 14 with the signal (SD1-SD2) made by subtracting the second sensing signal SD2 from the first sensing signal SD1. Note that the corresponding level of the clock signal SCLK changes as the motor switches switches, which is the so-called soft-cut technology. Specifically, the clock signal SCLK will alter the switches SW1 ̃SW4 of the full-bridge driving circuit 18 via the control circuit 16. However, even if supported by the soft-cut technology, if the switches SW1 ̃SW2 complete the “soft-cut” but the direction of the inductor current IL still doesn't immediately change, the inductor current IL will backflow to the supply voltage VCC via the turned-on switches SW1 ̃SW4 which are coupled to the supply voltage VCC and generate voltage surge at the output end as shown in the periods (d), (e) and (f) in FIG. 2.
Therefore, important issues when developing motor driving devices is to employ the soft-cut technology to drive motors with reduced noise, and employ protective devices to prevent the current of the motor to flow back to the supply voltage VCC.
BRIEF SUMMARY OF INVENTION
Provided is a motor driving device, used to generate at least one driving signal according to a clock signal and employ the at least one driving signal to control the rotation of a motor, comprising an inverter, a first processing unit, a second processing unit, a first buffering unit and a second buffering unit. The inverter is used to invert the clock signal and generate an inverse signal, the first processing unit is coupled to the inverter and is used to generate a first processing signal according to the inverse signal, and the second processing unit is used to generate a second processing signal according to the clock signal. Additionally, the first buffering unit is coupled to the first processing unit and is used to generate a first driving signal according to the first processing signal, and the second buffering unit is coupled to the second processing unit and is used to generate a second driving signal according to the second processing signal, wherein the at least one driving signal comprises the first driving signal and the second driving signal, and the motor driving device controls the rotation of the motor according to the first driving signal and the second driving signal.
A detailed description is given in the following embodiments with reference to the accompanying drawings.



BRIEF DESCRIPTION OF DRAWINGS
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
FIG. 1 illustrates a schematic diagram of a typical single-phase DC motor driving device.
FIG. 2 is the signal oscillogram of a typical motor driving device.
FIG. 3 is a schematic diagram of a motor driving device according to the present invention.
FIG. 4 is the signal oscillogram of a motor driving device according to the present invention.



DETAILED DESCRIPTION OF INVENTION
The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
Referring to FIG. 3, a schematic diagram of motor driving device according to the present invention is shown. As shown in FIG. 3, the present invention is a motor driving device 30, which generates at least a driving signal SC1 or SC2 according to a clock signal SCLK, and further uses the at least driving signal SC1 or SC2 to control the rotation of a motor 31. In one embodiment, the clock signal SCLK is a digital signal. The motor driving signal 30 comprises an inverter 36, a first processing unit 381, a second processing unit 382, a first buffering unit 401 and a second buffering unit 402. The inverter 36 is used to invert the clock signal SCLK and generate an inverse signal SIV. The first processing unit 381 is coupled to the inverter 36 and is used to generate a first processing signal SP1 according to the inverse signal SIV. The second processing unit 382 is used to generate a second signal SP2 according to the clock signal SCLK. The first buffering unit 401 is coupled to the first processing unit 381 and is used to generate a first driving signal SC1 according to the first processing signal SP1. The second buffering unit 402 is coupled to the second processing unit 382 and is used to generate a second driving signal SC2 according to the second processing signal SP2, wherein the at least driving signal SC1, SC2 comprises the first driving signal SC1 and the second driving signal SC2. Meanwhile, the motor driving device 30 employs the first driving signal SC1 and the second driving signal SC2 to control the motor 31 to rotate or stop, wherein the motor driving device 30 may be disposed in an integrated circuit.
In one embodiment, the motor driving device 30 comprises a Hall sensor 32 and a detecting device 34. The Hall sensor 32 is used to detect whether the motor 31 is rotating and generates a first sensing signal SD1 and a second sensing signal SD2. The detecting device 34 is coupled to the Hall sensor 32 and is used to generate the clock signal SCLK according to the first sensing signal SD1 and the second sensing signal SD2. In one embodiment, the detecting device 34 is a hysteresis comparator, which is used to compare the first sensing signal SD1 with the second sensing signal SD2 to generate the clock signal SCLK.
The first processing unit 381 comprises a first first voltage source VDD1, a first first current source I11, a first first transistor M11, a first second transistor M12, a first second current source I12 and a first first capacitor C11. The first first current source I11 is coupled to the first first voltage VDD1. The first first transistor M11 comprises a first first end, a first second end and a first third end, wherein the first first end is coupled to the first first current source I11, and the first second end is coupled to the output of the invertor 36 and is used to receive the inverse signal SIV. The first second transistor M12 comprises a second first end, a second second end and a second third end, wherein the second first end is coupled to the first third end of the first first transistor M11, the second second end is coupled to the output end of the inverter 36 and is used to receive the inverse signal SIV. The first second current I12 is coupled between the second third end of the first second transistor M12 and a ground VSS. The first first capacitor C11 comprises a first end and a second end, wherein the first end is coupled between the first third end of the first first transistor M11 and the second first end of the first second transistor M12, the second end is coupled to the ground VSS, and the first first capacitor C11 is used to charge and discharge to generate the first processing signal SP1.
The second processing unit 382 comprises a second first voltage VDD2, a second first current source I21, a second first transistor M21, a second second transistor M22, a second second current source I22 and a second first capacitor C21. The second first current source I21 is coupled to the second first voltage source VDD2. The second first transistor M21 comprises a first first end, a first second end and a first third end, wherein the first first end is coupled to the second first current source I22 and the first second end is coupled to the detecting device 34 and is used to receive the clock signal SCLK. The second second transistor M22 comprises a second first end, second second end and a second third end, the second first end is couplet to the first third end of the second first transistor M21, the second second end is coupled to the detecting device 34, and the second second end is used to receive the clock signal SCLK. The second second current source I22 is coupled between the second third end of the second second transistor M22 and the ground VSS. The second first capacitor C21 comprises a first end and a second end, wherein the first end is coupled between the first third end of the second first transistor M21 and the second first end of the second second transistor M22, the second end is coupled to the ground VSS, and the second first capacitor C21 is used to charge and discharge to generate the second processing signal SP2.
The first buffering unit 401 comprises a positive input end (+), a negative input end (−) and an output end, wherein the positive input end (+) is coupled to the first processing unit 381, and the negative input end (−) is coupled to the output end. The first buffing 401 is used to generate the first driving signal SC1 according to the first processing signal SP1, and further control the motor 31 to rotate or stop according to the first driving signal SC1. The second buffering unit 402 also comprises a positive input end (+), a negative input end (−) and an output end, the positive input end (+) of the second buffering unit 402 is coupled to the second processing unit 382, and the negative input end (−) of the second buffering unit 402 is coupled to the output end and is used to generate the second driving signal SC2 according to the second processing signal SP2 and further control the motor 31 to rotate or stop according to the second driving signal SC2. Each of the first buffering unit 401 and the second buffering unit 402 may be a unity gain buffer; and each of the output end of the first buffering unit 401 and the output end of the second buffering unit 402 may form a full-bridge driving circuit.
Referring to FIG. 4, the signal oscillogram of the motor driving devices according to the present invention is shown. A signal (SD1-SD2) generated by subtracting the second sensing signal SD2 from the first sensing signal SD1, the clock signal SCLK, and two driving signals SC1 and SC2 according to the present invention is shown in FIG. 4. The motor driving device 30 employs charge pumps as the first processing unit 381 and second processing unit 382 and employs the clock signal SCLK to control the charge pumps to charge or discharge. The motor driving device 30 control the charging/discharging time of the capacitors C11, C21 by changing the charging/discharging current I11, I12, I21, I22 of the charge pump and the size of the capacitors C11, C21, as shown in the periods (a), (b) and (c) in FIG. 4. Finally, soft-cut is achieved by driving the motor 31 via the unity gain buffer 401 and 402. Moreover, after coupling the unity gain buffer 401 and 402 to the charge pump (processing unit 381, 382) respectively, when the backflow occurs, the component coupled to the ground comprised in each output end of the two unity gain buffers 401 and 402 may be turned on due to the negative feedback mechanism, thus allowing the inductor current IL to be released so that the output voltage of the motor 31 may be controlled to the level as the output voltage of the charge pumps (processing unit 381, 382), as shown in the periods (d), (e), and (f) in FIG. 4. Therefore, the unity gain buffer 401 and 402 employed by the present motor driving device 30 prevents the inductor current IL from flowing back to the supply voltage VCC at the time when the motor 31 changes its phases.
Since the charge pumps and unity gain buffers are coupled with each other in cascade, the present motor driving device achieves the control method of soft-cut motor driving and stabilizes the output voltage of the motor to prevent backflow from occurring and flowing back to the supply voltage and causing damage to the motor driving circuit. Therefore, the present invention not only achieves soft-cut of the motor, but also efficiently prevents voltage surge, reduces noise of the motor, increases the reliability and operating range of systems, and solves the problems of the prior art.
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

## Claims

1. A motor driving device, used to generate at least one driving signal according to a clock signal and employ the at least one driving signal to control the rotation of a motor, comprising:
an inverter, used to invert the clock signal and generate an inverse signal;
a first processing unit, coupled to the inverter and is used to generate a first processing signal according to the inverse signal;
a second processing unit, used to generate a second processing signal according to the clock signal;
a first buffering unit, coupled to the first processing unit and is used to generate a first driving signal according to the first processing signal; and
a second buffering unit, coupled to the second processing unit and is used to generate a second driving signal according to the second processing signal,
wherein the at least one driving signal comprises the first driving signal and the second driving signal, and the motor driving device controls the rotation of the motor according to the first driving signal and the second driving signal.

2. A motor driving device as claimed in claim 1, further comprising:
a Hall sensor, used to detect whether the motor is rotating and generate a first sensing signal and a second sensing signal; and
a detecting device, coupled to the Hall sensor, used to generate the clock signal according to the first sensing signal and the second sensing signal.

3. A motor driving device as claimed in claim 2, wherein the clock signal is a digital signal.

4. A motor driving device as claimed in claim 2, wherein the detecting device is a hysteresis comparator, which is used to compare the first sensing signal with the second sensing signal and generate the clock signal.

5. A motor driving device as claimed in claim 1, wherein the first processing unit comprises:
a first first voltage source;
a first first current source, coupled to the first first voltage source;
a first first transistor, having a first first end, a first second end and a first third end, wherein the first first end is coupled to the first first current source, and the first second end is coupled to a output of the inverter and is used to receive the inverse signal at the first second end;
a first second transistor, having a second first end, a second second end and a second third end, wherein the second first end is coupled to the first third end of the first first transistor, the second second end is coupled to the output end of the inverter and is used to receive the reverse signal;
a first second current source, coupled between the second third end of the first second transistor and a ground; and
a first first capacitor, having a first end and a second end, wherein the first end is coupled to the first third end of the first first transistor and the second first end of the first second transistor, and the second end is coupled to the ground, and the first first capacitor is used to charge or discharge to generate the first processing signal.

6. A motor driving device as claimed in claim 5, wherein the second processing unit comprises:
a second first voltage source;
a second first current source, coupled to the second first voltage source;
a second first transistor, having a first first end, a first second end and a first third end, wherein the first first end is coupled to the second first current source, and the first second end is coupled to a detecting device and is used to receive the clock signal at the second second end;
a second second transistor, having a second first end, a second second end and a second third end, wherein the second first end is coupled to the first third end of the second first transistor, the second second end is coupled to the detecting device and is used to receive the clock signal;
a second second current source, coupled between the second third end of the second second transistor and the ground; and
a second first capacitor, having a first end and a second end, wherein the first end is coupled to the first third end of the second first transistor and the second first end of the second second transistor, and the second end is coupled to the ground, and the second first capacitor is used to charge or discharge to generate the second processing signal.

7. A motor driving device as claimed in claim 6, wherein the first buffering unit comprises a positive input end, a negative input end and an output end, wherein the positive input end is coupled to the first processing unit, the negative input end is coupled to the output end, and is used to generate the first driving signal according to the first processing signal and further accordingly control the motor to rotate or stop according to the first driving signal.

8. A motor driving device as claimed in claim 7, wherein the second buffering unit comprises a positive input end, a negative input end and an output end, wherein the positive input end is coupled to the second processing unit, the negative input end is coupled to the output end, and is used to generate the second driving signal according to the second processing signal and further control the motor to rotate or stop according to the second driving signal accordingly.

9. A motor driving device as claimed in claim 8, wherein each of the first buffering unit and the second buffering unit is a unity gain buffer.

10. A motor driving device as claimed in claim 8, wherein each of the output end of the first buffering unit and the output end of the second buffering unit is a full-bridge driving circuit.

11. A motor driving device as claimed in claim 1, wherein the motor driving circuit is an integrated circuit.