Abstract:
A drive and control circuit for motor system and the method thereof are disclosed. The motor system could be applied in a cooling device, wherein the motor system comprises a rotor, a coil and a bridge circuit. The drive and control circuit comprises a control unit, a state detecting circuit, a load determining circuit, and a startup setting circuit. The startup setting circuit makes the motor run with the maximum torque, thus to make the motor system start up easily and quickly. The load determining circuit detects the load of the motor system, thus to generate a load determining signal to determine the speed of the motor system. The control unit could be realized with few components so as to save the costs.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims priority to and the benefit of Chinese Patent Application No. 201110110111.4, filed Apr. 29, 2011, which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates generally to motor drive and control circuits and the method thereof, and more particularly but not exclusively to motor drive and control circuits which could startup a motor system with maximum torque and the method thereof. 
       BACKGROUND 
       [0003]    In real applications, motors often fail to start up with heavy load because of insufficient torque. There is a need to optimize the utilization of the power source to successfully start the motor and thereby shorten the transition time from stillness to rated speed. 
         [0004]      FIG. 1  shows a prior art drive and control circuit for a motor system. In  FIG. 1 , the drive and control circuit comprises a control circuit  101  and a power stage. The power stage comprises four switches SW 1 , SW 2 , SW 3  and SW 4 . The control circuit  101  generates four control signals PWM 1 , PWM 2 , PWM 3  and PWM 4  to respectively control the four switches SW 1 , SW 2 , SW 3  and SW 4 . The operation is: when the switches SW 1  and SW 4  are turned ON by the control signals PWM 1  and PWM 4 , the switches SW 2  and SW 3  are turned OFF by the control signals PWM 2  and PWM 3 , thus the current flowing through the motor  102  flows in direction a as shown in  FIG. 1 ; when the switches SW 2  and SW 3  are turned ON by the control signals PWM 2  and PWM 3 , the switches SW 1  and SW 4  are turned OFF by the control signals PWM 1  and PWM 4 , thus the current flowing through the motor  102  flows in direction b as shown in  FIG. 1 . By alternatively changing the direction of the current flowing through the motor  102 , the motor  102  runs with a fixed direction. 
         [0005]    During when the current flowing through the motor  102  flows in direction a, the switch SW 4  stays ON, and the switch SW 1  is turned ON and OFF at a frequency of 25 kHz. Similarly, during when the current flowing through the motor  102  flows in direction b, the switch SW 3  stays ON, and the switch SW 2  is also turned ON and OFF at a frequency of 25 kHz. 
         [0006]      FIG. 2  shows waveforms of signals in the circuit of  FIG. 1 . In  FIG. 2 , “Vcosc” represents a sawtooth signal and “Vth” represents a reference signal. “Speed” represents a pulse signal, and the frequency of the pulse signal is proportional to the speed of the motor. The sawtooth signal Vcosc is compared with the reference signal Vth to generate a control signal PWM. Persons of ordinary skill in the art should know that the control signal PWM is corresponding to the control signals PWM 1  or PWM 2  in  FIG. 1 . When the sawtooth signal Vcosc is fixed, the pulse width of the control signal PWM is determined by the reference signal Vth. As shown in  FIG. 2 , when the reference signal Vth is lower than the sawtooth signal Vcosc, the duty cycle of the control signal PWM could even be 100%, thus resulting in a maximum motor torque, and thereby resulting in a maximum motor speed. 
         [0007]    In real applications, the motor is expected to start up quickly so as to shorten the transition time from stillness to rated speed. Thus the duty cycle of the control signal PWM should be sufficient enough to achieve a maximum torque when the motor starts up. 
         [0008]      FIG. 3  shows the waveforms of signals in a conventional system with a control signal PWM having variable duty cycle. When the reference signal Vth is lower than the sawtooth signal Vcosc in the startup interval in  FIG. 3 , the control signal PWM has a 100% duty cycle, thereby the motor starts up with a high torque and gets started up easily and quickly. After the startup interval, the motor enters a steady state. The duty cycle of the control signal PWM changes to a set value determined by the changed reference signal Vth, and the speed of the motor is proportional to the duty cycle of the control signal PWM. 
         [0009]      FIG. 4  shows the waveforms of signals in a conventional system with a control signal PWM having a fixed duty cycle. As shown in  FIG. 4 , the duty cycle of the control signal PWM starts directly from a set value determined by the constant reference signal Vth. Thereby the motor has a much smaller torque than that in  FIG. 3 , resulting in a much longer transition time from stillness to rated speed. If started up with a heavy load, the motor may fail to start up due to insufficient torque. 
       SUMMARY 
       [0010]    The details and the advantages of the embodiments in accordance with the present disclosure are described in the following description. Many additional embodiments will be apparent to persons of ordinary skill in the art by reading this disclosure or by practicing the embodiments of the present disclosure. 
         [0011]    The present disclosure discloses a method which could startup a motor system with maximum torque in a short time. 
         [0012]    The method could startup a BLDC (Brushless DC) motor system with maximum torque. 
         [0013]    The present disclosure discloses a method of determining the load of the motor system, and controlling the speed of the motor system based on thereupon. 
         [0014]    The present disclosure discloses a drive and control circuit for motor system, comprising: a state detecting circuit configured to detect the state (run/stop) of the motor system, to provide a state detecting signal based thereupon; a load determining circuit configured to detect the ambient temperature of a fan driven by the motor system, to determine the load of the motor system and to generate a load determining signal based thereupon; and a startup setting circuit configured to generate a startup setting signal based on the operation of the motor system, and to generate a second control signal based on the startup setting signal, the load determining signal and the state detecting signal; and a control unit configured to control the operation of the motor system based on the state detecting signal and the second control signal. The startup setting circuit generates the startup setting signal when the motor system starts up, to make sure that the motor system starts up with a maximum torque. 
         [0015]    The present disclosure discloses a method of starting up a motor system with maximum torque, comprising: generating a state detecting signal by a state detecting circuit based on the state of the motor system, wherein the state of the motor system comprising a running state and a stop state; generating a load determining signal by a load determining circuit based on an ambient temperature of the fan driven by the motor system; generating a startup setting signal by a startup setting circuit when the motor system starts up; generating a second logic signal by a control unit based on the state detecting signal, the load determining signal and the startup setting signal; and generating control signals to control the bridge circuit of the motor system based on the second logic signal and the state detecting signal. The startup setting signal is provided when the motor system starts up, to make sure that the motor system starts up with a maximum torque. 
         [0016]    The drive and control circuit in accordance with the embodiments of the present disclosure drive the motor system with a maximum torque during the startup period and the restart period, thereby shorten the transition time from stillness to rated speed. In addition, the drive and control circuit is simplified and fewer external components are needed, so the cost is down. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  shows a prior art drive and control circuit for a motor system; 
           [0018]      FIG. 2  shows waveforms of signals in the circuit of  FIG. 1 ; 
           [0019]      FIG. 3  shows the waveforms of signals in a conventional system with a control signal PWM having variable duty cycle; 
           [0020]      FIG. 4  shows the waveforms of signals in a conventional system with a control signal PWM having a fixed duty cycle; 
           [0021]      FIG. 5  schematically shows a drive and control circuit for a motor system in accordance with an embodiment of the present disclosure; 
           [0022]      FIG. 6  schematically shows the waveforms of the signals in the circuit of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    In the present disclosure, numerous specific details are provided, such as examples of circuits, components, and methods, to provide a thorough understanding of embodiments of the disclosure. Persons of ordinary skill in the art will recognize, however, that the disclosure can be practiced without one or more of the specific details. In other instances, well-known details are not shown or described to avoid obscuring aspects of the disclosure. 
         [0024]    It is to be understood in these letters patent that the meaning of “A” is coupled to “B” is that either A and B are connected to each other as described below, or that, although A and B may not be connected to each other as described below, there is nevertheless a device or circuit that is connected to both A and B. This device or circuit may include active or passive circuit elements, where the passive circuit elements may be distributed or lumped-parameter in nature. For example, A may be connected to a circuit element that in turn is connected to B. 
         [0025]      FIG. 5  and  FIG. 6  schematically show the improvement of the torque control during the system&#39;s start-up in accordance with embodiments of the present disclosure. 
         [0026]      FIG. 5  schematically shows a drive and control circuit for a motor system in accordance with an embodiment of the present disclosure. The drive and control circuit comprises: a state detecting circuit  506  configured to detect the state (run/stop) of the motor system, to provide a state detecting signal based thereupon; a load determining circuit  503  configured to detect the ambient temperature of a fan driven by the motor system, to determine the load of the motor system and to generate a load determining signal based thereupon; a startup setting circuit  507  configured to generate a startup setting signal based on the operation of the motor system, and to generate a second control signal based on the startup setting signal, the load determining signal and the state detecting signal; a control unit  502  configured to control the operation of the motor system based on the state detecting signal and the second control signal. In one embodiment, the drive and control circuit for a motor system further comprises: a hall sensor  500  configured to generate two sine wave signals based on a position of a rotor to a coil in a motor system; and a comparator  501  configured to receive the sine wave signals, and to generate two square signals based on the two sine wave signals, wherein the two square signals are provided to the control unit  502  to change a direction of a current flowing through the motor system. 
         [0027]    In one embodiment, the startup setting circuit  507  generates the startup setting signal based on the operation of the motor system, and thereby generates a second control signal based on the startup setting signal, the load determining signal and the state detecting signal, wherein the second control signal controls the operation of the motor system. The startup setting circuit  507  generates the startup setting signal when the motor system starts up, to make sure that the motor system starts up with a maximum torque. 
         [0028]    In one embodiment, the startup setting circuit  507  comprises: a current source  508 , a capacitor C 54 , a second comparator  5071 , an AND gate AND 58  and an OR gate OR 59 . The current source  508  is configured to charge the capacitor C 54 . The second comparator  5071  having a first input terminal (inverting terminal), a second input terminal (non-inverting terminal) and an output terminal, wherein the first input terminal is configured to receive a voltage Vc 54  across the capacitor C 54 , the second input terminal is configured to receive a first reference signal VREF 1 , and wherein based on the comparison of the voltage Vc 54  and the first reference signal VREF 1 , the second comparator  5071  generates the startup setting signal at the output terminal. When the voltage Vc 54  is lower than the first reference signal VREF 1 , the startup setting signal is logical high; while when the voltage Vc 54  is higher than the first reference signal VREF 1 , the startup setting signal is logical low. 
         [0029]    The OR gate OR 59  is configured to receive the startup setting signal and the load determining signal, and based on the startup setting signal and the load determining signal, the OR gate OR 59  generates a first logic signal. The AND gate AND 58  receives the first logic signal and the state detecting signal, and based on the first logic signal and the state detecting signal, the AND gate AND 58  generates a second logic signal. 
         [0030]    In one embodiment, the load determining circuit  503  comprises: a minimum limit circuit  5031  configured to generate a minimum signal V LS ; a load sensing circuit  5032  configured to detect the ambient temperature of the fan driven by the motor system, to generate a threshold signal Vth based on the ambient temperature; a first comparator  5033  having a first input terminal, a second input terminal and a third input terminal, wherein the first input terminal is configured to receive the threshold signal Vth, the second input terminal is configured to receive the minimum signal V LS , and the third input terminal is configured to receive a sawtooth signal Vcosc, and wherein the first comparator  5033  generates the load determining signal based on the comparison of the sawtooth signal Vcosc with the lower one of the threshold signal Vth and the minimum signal V LS . 
         [0031]    In one embodiment, the minimum limit circuit  5031  comprises a first resistor R 51  and a second resistor R 52  coupled in series between the power supply Vcc and a ground node Vss. The minimum signal V LS  is generated at the connection node of the first resistor R 51  and the second resistor R 52 . Persons of ordinary skill in the art should know that the any suitable circuit for generating the minimum signal V LS  could be used without detracting the merits of the present disclosure. The minimum signal V LS  may have different values in different applications, as long as it is lower than the maximum withstanding voltage of the pin. 
         [0032]    In one embodiment, the temperature sensing circuit  5032  comprises a thermal resistor Rs and a third resistor R 53  coupled in series between the power supply Vcc and the ground node Vss, and the threshold signal Vth is generated at the connection node of the thermal resistor Rs and the third resistor R 53 . In one embodiment, the motor system is applied in a fan application. The fan is applied in a heat dissipation device for electrical equipment. When the electrical equipment gets hotter in the operation, the fan runs at a higher speed. In one embodiment, the thermal resistor Rs has negative temperature coefficient, and adheres to the fan to sense the ambient temperature. In normal operation, when the electrical equipment becomes hotter, the fan becomes hotter, too. Then the resistance of the thermal resistor Rs decreases, which causes the threshold signal Vth to decrease as shown in  FIG. 6 . Thus the threshold signal Vth reflects the ambient temperature of the fan. Persons of ordinary skill in the art should know that any suitable circuit which generates a signal reflecting the ambient temperature of the fan could be used without detracting the merits of the invention. 
         [0033]    The first comparator  5033  compares the threshold signal Vth with the minimum signal V LS , and sets the lower one as a load setting signal. The first comparator  5033  generates the load determining signal based on the comparison of the sawtooth signal Vcosc with the load setting signal. When the sawtooth signal Vcosc is higher than the load setting signal, the load determining signal is logical high. 
         [0034]    In one embodiment, the state detecting circuit  506  comprises: the capacitor C 54 , the current source  508 , a first NPN-type bipolar device Tr 56 , a second NPN-type bipolar device Tr 57 , a third comparator  5062 , a fourth comparator  5063  and an AND gate AND 55 . The state detecting circuit  506  receives a pulse signal provided by the control unit  502 . The pulse signal has pulses at the crossing point of the two square waveforms and reflects the state (run/stop) of the motor system. Based on the pulse signal, the state detecting circuit  506  generates the state detecting signal indicating the state (run/stop) of the motor system. The capacitor C 54  is charged by the current source  508  and is discharged when either the first NPN-type bipolar device Tr 56  or the second NPN-type bipolar device Tr 57  is turned ON. The charging and discharging of the capacitor C 54  results in a sawtooth voltage Vc 54 . 
         [0035]    In one embodiment, the third comparator  5062  has an inverting input terminal, a non-inverting input terminal and an output terminal, wherein the inverting input terminal is configured to receive a second reference signal VREF 2 , the non-inverting input terminal of the comparator  5062  is configured to receive the voltage Vc 54  across the capacitor C 54 , and wherein based on the voltage Vc 54  and the second reference signal VREF 2 , the third comparator  5062  generates a comparison signal at the output terminal; a fourth comparator  5063  having a non-inverting input terminal, an inverting input terminal and an output terminal, wherein the non-inverting input terminal is configured to receive the voltage Vc 54  across the capacitor, the inverting input terminal is configured to receive a third reference signal VREF 3 , and wherein based on the voltage Vc 54  and the third reference signal VREF 3 , the fourth comparator  5063  generates the state detecting signal at the output terminal. The state detecting signal is provided to a base terminal of the NPN-type bipolar device Tr 57 , the startup setting circuit  507  and the control unit  502 . 
         [0036]    In one embodiment, the first reference signal VREF 1 , the second reference signal VREF 2  and the third reference signal VREF 3  have a following relationship: 
         [0000]      VREF1&lt;VREF2&lt;VREF3 
         [0037]    When the voltage Vc 54  is higher than the second reference signal VREF 2 , the comparison signal generated by the third comparator  5062  is logical high, which turns on the NPN-type bipolar device Tr 56 . When the voltage Vc 54  is higher than the third reference signal VREF 3 , the state detecting signal generated by the fourth comparator  5063  is logical high, which turns on the NPN-type bipolar device Tr 57 . 
         [0038]    The bipolar device Tr 56  has a base terminal, a collector terminal and an emitter terminal, wherein the emitter terminal is configured to receive the second reference signal VREF 2 , the collector terminal is coupled to the connection node of the current source  508  and the capacitor C 54 , and the base terminal is coupled to an output terminal of the AND gate AND 55 . The bipolar device Tr 57  has a base terminal, a collector terminal and an emitter terminal, wherein the emitter terminal is connected to the ground node, the collector terminal is coupled to the connection node of the current source  508  and the capacitor C 54 , and the based terminal is configured to receive the state detecting signal generated by the fourth comparator  5063 . 
         [0039]    The AND gate AND 55  is configured to receive the pulse signal generated by the control unit  502  and the comparison signal generated by the third comparator  5062 . 
         [0040]    In one embodiment, the motor  102  comprises a rotor and a coil. The hall sensor  500  is placed in a preset position which is in the midperpendicular of the magnetic pole of the coil. The hall sensor  500  generates a pair of sine wave signals based on the position of the rotor. The comparator  501  features a hysteretic characteristic and is configured to receive the pair of sine wave signals, wherein based on the sine wave signals, the comparator  501  generates two square signals IN+ and IN−. The two square signals IN+ and IN− are the communication signals and determines the direction of the current flowing through the motor. 
         [0041]    The control unit  502  is configured to control the operation of the motor system based on the state detecting signal generated by the state detecting circuit  506  and the second control signal generated by the startup setting circuit  507 . 
         [0042]    The power stage comprises four switches SW 1 , SW 2 , SW 3  and SW 4 . The control unit  502  provides control signals PWM 1 , PWM 2 , PWM 3  and PWM 4  to respectively control the switches SW 1 , SW 2 , SW 3  and SW 4 . When the switches SW 1  and SW 4  are turned ON by the control signals PWM 1  and PWM 4 , the switches SW 2  and SW 3  are turned OFF by the control signals PWM 2  and PWM 4 , thus the current flowing through the motor flows in direction a as shown in  FIG. 5 ; when the switches SW 2  and SW 3  are turned ON by the control signals PWM 2  and PWM 3 , the switches SW 1  and SW 4  are turned OFF by the control signals PWM 1  and PWM 4 , thus the current flowing through the motor flows in direction b as shown in  FIG. 5 . By alternatively changing the direction of the current flowing through the motor, the motor runs with a fixed direction. 
         [0043]    In one embodiment, during when the current flowing through the motor flows in direction a, the switch SW 4  stays ON and the switch SW 1  is turned ON and OFF with a frequency of 25 kHz; and during when the current flowing through the motor flows in direction b, the switch SW 3  stays ON and the switch SW 2  is also turned ON and OFF with a frequency of 25 kHz. 
         [0044]      FIG. 6  shows the waveforms of the signals in the circuit of  FIG. 5 . In  FIG. 6 , the two square signals IN+ and IN− are generated by the comparator  501 ; the threshold signal Vth is generated by the temperature sensing circuit  5032 ; the sawtooth signal Vcosc is generated by an oscillator  5034 ; the minimum signal V LS  is generated by the minimum limit circuit  5031 ; Vcosc(max) and Vcosc(min) respectively represent the maximum value and the minimum value of the sawtooth signal Vcosc; PWM represents any one of the control signals PWM 1 , PWM 2 , PWM 3  and PWM 4  generated by the control unit  502 ; and Vc 54  represents the voltage across the capacitor C 54 . a    
         [0045]    During subinterval t 0 ˜t 1 : the voltage Vc 54  across the capacitor C 54  is lower than the first reference signal VREF 1 , so the startup setting signal generated by the second comparator  5071  is logical high. As a result, the first logic signal generated by the OR gate OR 59  is logical high during this period, which means that the signal PWM has the maximum duty cycle and the motor system will startup with the maximum torque. 
         [0046]    During subinterval t 1 ˜t 2  (V LS &lt;Vth): the voltage Vc 54  increases. When the voltage Vc 54  goes higher than the first reference signal VREF 1 , the startup setting signal generated by the second comparator  5071  is logical low. Then the first logic signal generated by the OR gate OR 59  is determined by the load determining signal generated by the load determining circuit  503 . The first comparator  5033  sets the lower one of the minimum signal V LS  and the threshold signal Vth as the load setting signal, and compares the load setting signal with the sawtooth signal Vcosc. As shown in  FIG. 6 , the load determining signal is logical high when the sawtooth signal Vcosc is higher than the load setting signal, which is reflected by the waveform of signal PWM. The pulse signal generated by the control unit  502  may be blocked by the AND gate AND 55  when the comparison signal generated by the comparator  5062  is logical low. For example, at time t 1 - a , the pulse signal is logical high because of the change of the current direction as seen from waveform of two square signals in  FIG. 6 . At this moment, the voltage Vc 54  is lower than the second reference signal VREF 2 , so the comparison signal generated by the second comparator  5062  is logical low. Thus the logical high pulse signal is blocked and the signal generated by the AND gate AND 55  is logical low, and the voltage Vc 54  keeps increasing. At time t 1 - b , the pulse signal is again logical high. At this moment, the voltage Vc 54  is higher than the second reference signal VREF 2 , so the comparison signal generated by the second comparator  5062  is logical high. Then the signal generated by the AND gate AND 55  is logical low, and the bipolar device Tr 56  is turned ON. The capacitor C 54  is discharged and the voltage Vc 54  decreases to VREF 2 . 
         [0047]    During time subinterval t 2 ˜t 3  (V LS &gt;Vth): the ambient temperature increases, resulting in a decrease of the threshold signal Vth. When the threshold signal Vth is lower than the minimum signal V LS , the minimum signal V LS  is set as the load setting signal. 
         [0048]    During time t 2 ˜t 3 , the load determining signal generated by the first comparator  5033  is logical high when the sawtooth signal Vcosc is higher than the load setting signal. 
         [0049]    During subinterval t 3 ˜t 4 : the state detecting signal generated by the fourth comparator  5063  is provided to the base terminal of the bipolar device Tr 57  and an input terminal of the AND gate AND 58 . If the motor system is forced to stop, the two square signals will remain unchanged as shown in  FIG. 6 . Then the pulse signal generated by the control unit  502  stays low, and the bipolar device Tr 56  stays OFF. The voltage Vc 54  increases to the third reference signal VREF 3  at time t 3  (as shown in  FIG. 6 ). Then the state detecting signal becomes logical high and turns ON the bipolar device Tr 57  to discharge the capacitor C 54 , as shown in the subinterval t 3 ˜t 4 . 
         [0050]    During subinterval t 4 ˜t 5 : the capacitor C 54  is discharged by the bipolar device Tr 57  and the voltage Vc 54  decreases to zero at time t 4 . From time t 4 , the load determining signal generated by the first comparator  5033  controls to drive the motor system again. Meanwhile, the capacitor C 54  is charged again. When the voltage Vc 54  is lower than the first reference signal VREF 1 , the comparison signal generated by the second comparator  5071  becomes logical high, and the motor system will restart with the maximum torque, as shown in the subinterval t 4 ˜t 5  in  FIG. 6 . 
         [0051]    During subinterval t&gt;t 5 : when the voltage Vc 54  is higher than the first reference signal VREF 1 , the startup setting signal is logical low and the load is determined by the load determining signal generated by the first comparator  5033 , as shown in the subinterval t&gt;t 5  in  FIG. 6 . The threshold signal Vth decreases as the ambient temperature increases. The threshold signal Vth is lower than the minimum value Vcosc(min) of the sawtooth signal Vcosc during subinterval t&gt;t 5 , so the duty cycle of the load determining signal is 100%. 
         [0052]    Several embodiments of the foregoing drive and control circuit for a motor system provide better performance compared to conventional technique discussed above. Unlike the conventional technique, several embodiments of the drive and control circuit drive the motor system with a maximum torque during the startup period and the restart period, and the speed of the motor system is adjusted according to the load during normal operation. In addition, the drive and control circuit is simplified and may be integrated. Furthermore, several embodiments of the drive and control circuit need fewer external components (only circuit  5031  and circuit  5032  are needed), so the cost is down. 
         [0053]    An effective technique for drive and control the motor system has been disclosed. While specific embodiments of the present disclosure have been provided, it is to be understood that these embodiments are for illustration purposes and not limiting. Many additional embodiments will be apparent to persons of ordinary skill in the art by reading this disclosure.