Patent Publication Number: US-10763766-B2

Title: Magnetic sensor and an integrated circuit

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 15/230,941 filed Aug. 8, 2016, which is a continuation-in-part of U.S. patent application Ser. No. 14/822,353 filed Aug. 10, 2015 (issued as U.S. Pat. No. 9,755,555 on Sep. 5, 2017), which claims priority to Chinese Patent Application No. 201410390592.2, filed on Aug. 8, 2014 and to Chinese Patent Application No. 201410404474.2, filed on Aug. 15, 2014. In addition, this non-provisional patent application claims priority under the Paris Convention to PCT Patent Application No. PCT/CN2015/086422, filed with the Chinese Patent Office on Aug. 7, 2015, to Chinese Patent Application No. CN 201610203682.5, filed with the Chinese Patent Office on Apr. 1, 2016, and to Chinese Patent Application No. CN 201610392501.8, filed with the Chinese Patent Office on Jun. 2, 2016 all of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present teaching relates to a field of circuit technology. In particular, the present teaching relates to a magnetic sensor. The present teaching further relates to a driver for a low-power permanent magnetic motor. 
     2. Discussion of Technical Background 
     During starting of a synchronous motor, the stator produces an alternating magnetic field causing the permanent magnetic rotor to be oscillated. The amplitude of the oscillation of the rotor increases until the rotor begins to rotate, and finally the rotor is accelerated to rotate in synchronism with the alternating magnetic field of the stator. To ensure the starting of a conventional synchronous motor, a starting point of the motor is set to be low, which results in that the motor cannot operate at a relatively high working point, thus the efficiency is low. In another aspect, the rotor cannot be ensured to rotate in a same direction every time since a stop or stationary position of the permanent magnetic rotor is not fixed. Accordingly, in applications such as a fan and water pump, the impeller driven by the rotor has straight radial vanes, which results in a low operational efficiency of the fan and water pump. 
       FIG. 1  illustrates a conventional drive circuit for a synchronous motor, which allows a rotor to rotate in a same predetermined direction in every time it starts. In the circuit, a stator winding  1  of the motor is connected in series with a TRIAC between two terminals M and N of an AC power source VM, and an AC power source VM is converted by a conversion circuit DC into a direct current voltage and the direct current is supplied to a position sensor H. A magnetic pole position of a rotor in the motor is detected by the position sensor H, and an output signal Vh of the position sensor H is connected to a switch control circuit PC to control the bidirectional thyristor T. 
       FIG. 2  illustrates a waveform of the drive circuit. It can be seen from  FIG. 2  that, in the drive circuit, no matter the bidirectional thyristor T is switched on or off, the AC power source supplies power for the conversion circuit DC so that the conversion circuit DC constantly outputs and supplies power for the position sensor H (referring to a signal VH in  FIG. 2 ). In a low-power application, in a case that the AC power source is commercial electricity of about 200V, the electric energy consumed by two resistors R 2  and R 3  in the conversion circuit DC is more than the electric energy consumed by the motor. 
     The magnetic sensor applies Hall effect, in which, when current I runs through a substance and a magnetic field B is applied in a positive angle with respect to the current I, a potential difference V is generated in a direction perpendicular to the direction of current I and the direction of the magnetic field B. The magnetic sensor is often implemented to detect the magnetic polarity of an electric rotor. 
     As the circuit design and signal processing technology advances, there is a need to improve the magnetic sensor and the implemented IC for the ease of use and accurate detection. 
     SUMMARY 
     The present teaching provides a magnetic sensor and application(s) thereof. In one embodiment, the present teaching discloses a magnetic sensor that comprises a housing, an input and an output port, both extending from the housing, and an electrical circuit. The input port is connected to an external alternating current (AC) power supply. The electrical circuit includes an output control circuit coupled with the output port and configured to be at least responsive to a magnetic induction signal to control the magnetic sensor to operate in at least one of a first state and a second state. In the first state, a load current flows in a first direction from the output port to outside of the magnetic sensor. In the second state, a load current flows in a second direction opposite of the first direction from outside of the magnetic sensor into the magnetic sensor via the output port. The operating frequency of the magnetic sensor is positively proportional to the frequency of the external AC power supply. 
     In a different embodiment, the present teaching discloses a magnetic sensor that includes a housing, an input port extending from the housing and coupled with an external AC power supply, an output port extending from the housing, and an electrical circuit. The electrical circuit comprises an output control circuit coupled with the output port and configured to be at least responsive to a magnetic induction signal and the external AC power supply to control the magnetic sensor to operate in a state in which a load current flows through the output port. The magnetic induction signal is indicative of at least one characteristic of an external magnetic field detected by the electrical circuit and the operating frequency of the magnetic sensor is positively proportional to the frequency of the external AC power supply. 
     In another different embodiment, the present teaching discloses an integrated circuit, which includes an input port and an output port, wherein the input port is to be connected to an external AC power supply, and an electrical circuit. The electrical circuit comprises an output control circuit coupled with the output port and configured to be at least responsive to a detected signal to control the integrated circuit to operate in at least one of a first and a second state. In the first state, a load current flows in a first direction from the output port to outside of the integrated circuit. In the second state, a load current flows in a second direction opposite of the first direction from outside of the integrated circuit into the integrated circuit via the output port. The operating frequency of the integrated circuit is positively proportional to the frequency of the external AC power supply. 
     In yet another embodiment, the present teaching discloses a motor assembly, which comprises a motor configured to operate based on an AC power supply, a magnetic sensor configured to detect a magnetic field generated by the motor and operate in an operating state determined based on the detected magnetic field, and a bi-directional AC switch serially coupled with the motor and configured to control the motor based on the operating state of the magnetic sensor. The magnetic sensor includes an input port and an output port, wherein the input port is coupled with the external AC power supply and the output port is coupled with a control terminal of the bi-directional AC switch and an electrical circuit which comprises an output control circuit configured to be at least responsive to a magnetic induction signal, indicative of at least one characteristic of the magnetic field, to control the magnetic sensor to operate in at least one of a first state and a second state. In operation, in the first state, a load current flows in a first direction from the output port to the bi-directional AC switch. In the second state, a load current flows in a second direction opposite of the first direction from the bi-directional AC switch to the magnetic sensor via the output port. The operating frequency of the magnetic sensor is positively proportional to the frequency of the external AC power supply. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The methods, systems, and/or programming described herein are further described in terms of exemplary embodiments. These exemplary embodiments are described in detail with reference to the drawings. These embodiments are non-limiting exemplary embodiments, in which like reference numerals represent similar structures throughout the several views of the drawings, and wherein: 
         FIG. 1  illustrates a prior art drive circuit for a synchronous motor, according to an embodiment of the present teaching; 
         FIG. 2  illustrates a waveform of the drive circuit shown in  FIG. 1 ; 
         FIG. 3  illustrates a diagrammatic representation of a synchronous motor, according to an embodiment of the present teaching; 
         FIG. 4  illustrates a block diagram of a drive circuit for a synchronous motor, according to an embodiment of the present teaching; 
         FIG. 5  illustrates a drive circuit for a synchronous motor, according to an embodiment of the present teaching; 
         FIG. 6  illustrates a waveform of the drive circuit shown in  FIG. 5 ; 
         FIGS. 7 to 10  illustrate different embodiments of a drive circuit of a synchronous motor, according to an embodiment of the present teaching; 
         FIG. 11  illustrates an exemplary diagram of a magnetic sensor  1105  according to an embodiment of the present teaching; 
         FIG. 12  illustrates an exemplary diagram of the magnetic sensor  1105  according to a different embodiment of the present teaching; 
         FIG. 13  illustrates an exemplary diagram of the magnetic sensor  1105  according to yet another embodiment of the present teaching; 
         FIG. 14  illustrates an exemplary implementation of the output control circuit  1120  according to an embodiment of the present teaching; 
         FIG. 15  illustrates an exemplary implementation of the output control circuit  1120  according to another embodiment of the present teaching; 
         FIG. 16  illustrates another exemplary diagram of the magnetic sensor  1105  according to yet another embodiment of the present teaching; 
         FIG. 17  illustrates an exemplary diagram of the rectifier  1150  according to an embodiment of the present teaching; 
         FIG. 18  illustrates an exemplary diagram of the magnetic sensor  1105  according to yet another embodiment of the present teaching; 
         FIG. 19  illustrates an exemplary implementation circuit of a part of the magnetic sensor  1105  according to yet another embodiment of the present teaching; 
         FIG. 20  illustrates another embodiment of the output control circuit  1120  in connection with the state control circuit  1140 ; 
         FIG. 21  is a flowchart of an exemplary method of signal processing performed by the magnetic sensor  1105 , according to an embodiment of the present teaching; 
         FIG. 22  illustrates an exemplary diagram of a motor assembly  2200  incorporating the magnetic sensor discussed herein, according to an embodiment of the present teaching; 
         FIG. 23  illustrates an exemplary diagram of a motor  2300  according to an embodiment of the present teaching; and 
         FIG. 24  illustrates the waveforms of an output voltage from an AC power supply  1610  and the rectifier bridge  1150 , respectively, according to an embodiment of the present teaching. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant teachings. However, it should be apparent to those skilled in the art that the present teachings may be practiced without such details. In other instances, well known methods, procedures, systems, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present teachings. 
     Throughout the specification and claims, terms may have nuanced meanings suggested or implied in context beyond an explicitly stated meaning. Likewise, the phrase “in one embodiment/example” as used herein does not necessarily refer to the same embodiment and the phrase “in another embodiment/example” as used herein does not necessarily refer to a different embodiment. It is intended, for example, that claimed subject matter include combinations of example embodiments in whole or in part. 
     In general, terminology may be understood at least in part from usage in context. For example, terms, such as “and”, “or”, or “and/or,” as used herein may include a variety of meanings that may depend at least in part upon the context in which such terms are used. Typically, “or” if used to associate a list, such as A, B or C, is intended to mean A, B, and C, here used in the inclusive sense, as well as A, B or C, here used in the exclusive sense. In addition, the term “one or more” as used herein, depending at least in part upon context, may be used to describe any feature, structure, or characteristic in a singular sense or may be used to describe combinations of features, structures or characteristics in a plural sense. Similarly, terms, such as “a,” “an,” or “the,” again, may be understood to convey a singular usage or to convey a plural usage, depending at least in part upon context. In addition, the term “based on” may be understood as not necessarily intended to convey an exclusive set of factors and may, instead, allow for existence of additional factors not necessarily expressly described, again, depending at least in part on context. 
       FIG. 3  schematically shows a synchronous motor according to an embodiment of the present invention. The synchronous motor  10  includes a stator  12  and a permanent magnet rotor  14  rotatably disposed between magnetic poles of the stator  12 , and the stator  12  includes a stator core  15  and a stator winding  16  wound on the stator core  15 . The rotor  14  includes at least one permanent magnet forming at least one pair of permanent magnetic poles with opposite polarities, and the rotor  14  operates at a constant rotational speed of 60 f/p during a steady state phase in a case that the stator winding  16  is connected to an AC power supply, where f is a frequency of the AC power supply and p is the number of pole pairs of the rotor. 
     Non-uniform gap  18  is formed between the magnetic poles of the stator  12  and the permanent magnetic poles of the rotor  14  so that a polar axis R of the rotor  14  has an angular offset a relative to a central axis S of the stator  12  in a case that the rotor is at rest. The rotor  14  may be configured to have a fixed starting direction (a clockwise direction in this embodiment as shown by the arrow in  FIG. 3 ) every time the stator winding  16  is energized. The stator and the rotor each have two magnetic poles as shown in  FIG. 3 . It can be understood that, in other embodiments, the stator and the rotor may also have more magnetic poles, such as 4 or 6 magnetic poles. 
     A position sensor  20  for detecting the angular position of the rotor is disposed on the stator  12  or at a position near the rotor inside the stator, and the position sensor  20  has an angular offset relative to the central axis S of the stator. Preferably, this angular offset is also a, as in this embodiment. Preferably, the position sensor  20  is a Hall effect sensor. 
       FIG. 4  shows a block diagram of a drive circuit for a synchronous motor according to an embodiment of the present invention. In the drive circuit  22 , the stator winding  16  and the AC power supply  24  are connected in series between two nodes A and B. Preferably, the AC power supply  24  may be a commercial AC power supply with a fixed frequency, such as 50 Hz or 60 Hz, and a supply voltage may be, for example, 110V, 220V or 230V. A controllable bidirectional AC switch  26  is connected between the two nodes A and B, in parallel with the stator winding  16  and the AC power supply  24 . Preferably, the controllable bidirectional AC switch  26  is a TRIAC, of which two anodes are connected to the two nodes A and B respectively. It can be understood that, the controllable bidirectional AC switch  26  alternatively may be two silicon control rectifiers reversely connected in parallel, and control circuits may be correspondingly configured to control the two silicon control rectifiers in a preset way. An AC-DC conversion circuit  28  is also connected between the two nodes A and B. An AC voltage between the two nodes A and B is converted by the AC-DC conversion circuit  28  into a low voltage DC. The position sensor  20  may be powered by the low voltage DC output by the AC-DC conversion circuit  28 , for detecting the magnetic pole position of the permanent magnet rotor  14  of the synchronous motor  10  and outputting a corresponding signal. A switch control circuit  30  is connected to the AC-DC conversion circuit  28 , the position sensor  20  and the controllable bidirectional AC switch  26 , and is configured to control the controllable bidirectional AC switch  26  to be switched between a switch-on state and a switch-off state in a predetermined way, based on the magnetic pole position of the permanent magnet rotor which is detected by the position sensor and polarity information of the AC power supply  24  which may be obtained from the AC-DC conversion circuit  28 , such that the stator winding  16  urges the rotor  14  to rotate only in the above-mentioned fixed starting direction during a starting phase of the motor. According to this embodiment of the present invention, in a case that the controllable bidirectional AC switch  26  is switched on, the two nodes A and B are shorted, the AC-DC conversion circuit  28  does not consume electric energy since there is no current flowing through the AC-DC conversion circuit  28 , hence, the utilization efficiency of electric energy can be improved significantly. 
       FIG. 5  shows a circuit diagram of a drive circuit  40  for a synchronous motor according to a first embodiment of the present disclosure. The stator winding  16  of the synchronous motor is connected in series with the AC power supply  24  between the two nodes A and B. A first anode T 1  of the TRIAC  26  is connected to the node A, and a second anode T 2  of the TRIAC  26  is connected to the node B. The AC-DC conversion circuit  28  is connected in parallel with the TRIAC  26  between the two nodes A and B. An AC voltage between the two nodes A and B is converted by the AC-DC conversion circuit  28  into a low voltage DC (preferably, low voltage ranges from 3V to 18V). The AC-DC conversion circuit  28  includes a first zener diode Z 1  and a second zener diode Z 2  which are reversely connected in parallel between the two nodes A and B via a first resistor R 1  and a second resistor R 2  respectively. A high voltage output terminal C of the AC-DC conversion circuit  28  is formed at a connection point of the first resistor R 1  and a cathode of the first zener diode Z 1 , and a low voltage output terminal D of the AC-DC conversion circuit  28  is formed at a connection point of the second resistor R 2  and an anode of the second zener diode Z 2 . The voltage output terminal C is connected to a positive power supply terminal of the position sensor  20 , and the voltage output terminal D is connected to a negative power supply terminal of the position sensor  20 . Three terminals of the switch control circuit  30  are connected to the high voltage output terminal C of the AC-DC conversion circuit  28 , an output terminal H 1  of the position sensor  20  and a control electrode G of the TRIAC  26  respectively. The switch control circuit  30  includes a third resistor R 3 , a fifth diode D 5 , and a fourth resistor R 4  and a sixth diode D 6  connected in series between the output terminal HI of the position sensor  20  and the control electrode G of the controllable bidirectional AC switch  26 . An anode of the sixth diode D 6  is connected to the control electrode G of the controllable bidirectional AC switch  26 . One terminal of the third resistor R 3  is connected to the high voltage output terminal C of the AC-DC conversion circuit  28 , and the other terminal of the third resistor R 3  is connected to an anode of the fifth diode D 5 . A cathode of the fifth diode D 5  is connected to the control electrode G of the controllable bidirectional AC switch  26 . 
     In conjunction with  FIG. 6 , an operational principle of the drive circuit  40  is described. In  FIG. 6 , Vac indicates a waveform of voltage of the AC power supply  24 , and lac indicates a waveform of current flowing through the stator winding  16 . Due to the inductive character of the stator winding  16 , the waveform of current Iac lags behind the waveform of voltage Vac. V 1  indicates a waveform of voltage between two terminals of the first zener diode Z 1 , V 2  indicates a waveform of voltage between two terminals of the second zener diode Z 2 , Vdc indicates a waveform of voltage between two output terminals C and D of the AC-DC conversion circuit  28 , Ha indicates a waveform of a signal output by the output terminal H 1  of the position sensor  20 , and Hb indicates a rotor magnetic field detected by the position sensor  20 . In this embodiment, in a case that the position sensor  20  is powered normally, the output terminal HI outputs a logic high level in a case that the detected rotor magnetic field is North, or the output terminal H 1  outputs a logic low level in a case that the detected rotor magnetic field is South. 
     In a case that the rotor magnetic field Hb detected by the position sensor  20  is North, in a first positive half cycle of the AC power supply, the supply voltage is gradually increased from a time instant t 0  to a time instant t 1 , the output terminal H 1  of the position sensor  20  outputs a high level, and a current flows through the resistor R 1 , the resistor R 3 , the diode D 5  and the control electrode G and the second anode T 2  of the TRIAC  26  sequentially. The TRIAC  26  is switched on in a case that a drive current flowing through the control electrode G and the second anode T 2  is greater than a gate triggering current Ig. Once the TRIAC  26  is switched on, the two nodes A and B are shorted, a current flowing through the stator winding  16  in the motor is gradually increased until a large forward current flows through the stator winding  16  to drive the rotor  14  to rotate clockwise as shown in  FIG. 3 . Since the two nodes A and B are shorted, there is no current flowing through the AC-DC conversion circuit  28  from the time instant t 1  to a time instant t 2 . Hence, the resistors R 1  and R 2  do not consume electric energy, and the output of the position sensor  20  is stopped due to no power is supplied. Since the current flowing through two anodes T 1  and T 2  of the TRIAC  26  is large enough (which is greater than a holding current Ihold), the TRIAC  26  is kept to be switched on in a case that there is no drive current flowing through the control electrode G and the second anode T 2 . In a negative half cycle of the AC power supply, after a time instant t 3 , a current flowing through T 1  and T 2  is less than the holding current Ihold, the TRIAC  26  is switched off, a current begins to flow through the AC-DC conversion circuit  28 , and the output terminal HI of the position sensor  20  outputs a high level again. Since a potential at the point C is lower than a potential at the point E, there is no drive current flowing through the control electrode G and the second anode T 2  of the TRIAC  26 , and the TRIAC  26  is kept to be switched off. Since the resistance of the resistors R 1  and R 2  in the AC-DC conversion circuit  28  are far greater than the resistance of the stator winding  16  in the motor, a current currently flowing through the stator winding  16  is far less than the current flowing through the stator winding  16  from the time instant t 1  to the time instant t 2  and generates very small driving force for the rotor  14 . Hence, the rotor  14  continues to rotate clockwise due to inertia. In a second positive half cycle of the AC power supply, similar to the first positive half cycle, a current flows through the resistor R 1 , the resistor R 3 , the diode D 5 , and the control electrode G and the second anode T 2  of the TRIAC  26  sequentially. The TRIAC  26  is switched on again, and the current flowing through the stator winding  16  continues to drive the rotor  14  to rotate clockwise. Similarly, the resistors R 1  and R 2  do not consume electric energy since the two nodes A and B are shorted. In the next negative half cycle of the power supply, the current flowing through the two anodes T 1  and T 2  of the TRIAC  26  is less than the holding current Ihold, the TRIAC  26  is switched off again, and the rotor continues to rotate clockwise due to the effect of inertia. 
     At a time instant t 4 , the rotor magnetic field Hb detected by the position sensor  20  changes to be South from North, the AC power supply is still in the positive half cycle and the TRIAC  26  is switched on, the two nodes A and B are shorted, and there is no current flowing through the AC-DC conversion circuit  28 . After the AC power supply enters the negative half cycle, the current flowing through the two anodes T 1  and T 2  of the TRIAC  26  is gradually decreased, and the TRIAC  26  is switched off at a time instant t 5 . Then the current flows through the second anode T 2  and the control electrode G of the TRIAC  26 , the diode D 6 , the resistor R 4 , the position sensor  20 , the resistor R 2  and the stator winding  16  sequentially. As the drive current is gradually increased, the TRIAC  26  is switched on again at a time instant t 6 , the two nodes A and B are shorted again, the resistors RI and R 2  do not consume electric energy, and the output of the position sensor  20  is stopped due to no power is supplied. There is a larger reverse current flowing through the stator winding  16 , and the rotor  14  continues to be driven clockwise since the rotor magnetic field is South. From the time instant t 5  to the time instant t 6 , the first zener diode Z 1  and the second zener diode Z 2  are switched on, hence, there is a voltage output between the two output terminals C and D of the AC-DC conversion circuit  28 . At a time instant t 7 , the AC power supply enters the positive half cycle again, the TRIAC  26  is switched off when the current flowing through the TRIAC  26  crosses zero, and then a voltage of the control circuit is gradually increased. As the voltage is gradually increased, a current begins to flow through the AC-DC conversion circuit  28 , the output terminal H 1  of the position sensor  20  outputs a low level, there is no drive current flowing through the control electrode G and the second anode T 2  of the TRIAC  26 , hence, the TRIAC  26  is switched off. Since the current flowing through the stator winding  16  is very small, nearly no driving force is generated for the rotor  14 . At a time instant t 8 , the power supply is in the positive half cycle, the position sensor outputs a low level, the TRIAC  26  is kept to be switched off after the current crosses zero, and the rotor continues to rotate clockwise due to inertia. According to an embodiment of the present invention, the rotor may be accelerated to be synchronized with the stator after rotating only one circle after the stator winding is energized. 
     In the embodiment of the present invention, by taking advantage of a feature of a TRIAC that the TRIAC is kept to be switched on although there is no drive current flowing though the TRIAC once the TRIAC is switched on, it is avoided that a resistor in the AC-DC conversion circuit still consumes electric energy after the TRIAC is switched on, hence, the utilization efficiency of electric energy can be improved significantly. 
       FIG. 7  shows a circuit diagram of a drive circuit  42  for a synchronous motor according to an embodiment of the present disclosure. The stator winding  16  of the synchronous motor is connected in series with the AC power supply  24  between the two nodes A and B. A first anode T 1  of the TRIAC  26  is connected to the node A, and a second anode T 2  of the TRIAC  26  is connected to the node B. The AC-DC conversion circuit  28  is connected in parallel with the TRIAC  26  between the two nodes A and B. An AC between the two nodes A and B is converted by the AC-DC conversion circuit  28  into a low voltage DC, preferably, a low voltage ranging from 3V to 18V. The AC-DC conversion circuit  28  includes a first resistor RI and a full wave bridge rectifier connected in series between the two nodes A and B. The full wave bridge rectifier includes two rectifier branches connected in parallel, one of the two rectifier branches includes a first diode D 1  and a third diode D 3  reversely connected in series, and the other of the two rectifier branches includes a second zener diode Z 2  and a fourth zener diode Z 4  reversely connected in series, the high voltage output terminal C of the AC-DC conversion circuit  28  is formed at a connection point of a cathode of the first diode D 1  and a cathode of the third diode D 3 , and the low voltage output terminal D of the AC-DC conversion circuit  28  is formed at a connection point of an anode of the second zener diode Z 2  and an anode of the fourth zener diode Z 4 . The output terminal C is connected to a positive power supply terminal of the position sensor  20 , and the output terminal D is connected to a negative power supply terminal of the position sensor  20 . The switch control circuit  30  includes a third resistor R 3 , a fourth resistor R 4 , and a fifth diode D 5  and a sixth diode D 6  reversely connected in series between the output terminal H 1  of the position sensor  20  and the control electrode G of the controllable bidirectional AC switch  26 . A cathode of the fifth diode D 5  is connected to the output terminal H 1  of the position sensor, and a cathode of the sixth diode D 6  is connected to the control electrode G of the controllable bidirectional AC switch. One terminal of the third resistor R 3  is connected to the high voltage output terminal C of the AC-DC conversion circuit, and the other terminal of the third resistor R 3  is connected to a connection point of an anode of the fifth diode D 5  and an anode of the sixth diode D 6 . Two terminals of the fourth resistor R 4  are connected to a cathode of the fifth diode D 5  and a cathode of the sixth diode D 6  respectively. 
       FIG. 8  shows a circuit diagram of a drive circuit  44  for a synchronous motor according to a further embodiment of the present invention. The drive circuit  44  is similar to the drive circuit  42  in the previous embodiment and, the drive circuit  44  differs from the drive circuit  42  in that, the zener diodes Z 2  and Z 4  in the drive circuit  42  are replaced by general diodes D 2  and D 4  in the rectifier of the drive circuit  44 . In addition, a zener diode Z 7  is connected between the two output terminals C and D of the AC-DC conversion circuit  28  in the drive circuit  44 . 
       FIG. 9  shows a circuit diagram of a drive circuit  46  for a synchronous motor according to further embodiment of the present invention. The stator winding  16  of the synchronous motor is connected in series with the AC power supply  24  between the two nodes A and B. A first anode T 1  of the TRIAC  26  is connected to the node A, and a second anode T 2  of the TRIAC  26  is connected to the node B. The AC-DC conversion circuit  28  is connected in parallel with the TRIAC  26  between the two nodes A and B. An AC voltage between the two nodes A and B is converted by the AC-DC conversion circuit  28  into a low voltage DC, preferably, a low voltage ranging from 3V to 18V. The AC-DC conversion circuit  28  includes a first resistor R 1  and a full wave bridge rectifier connected in series between the two nodes A and B. The full wave bridge rectifier includes two rectifier branches connected in parallel, one of the two rectifier branches includes two silicon control rectifiers S 1  and S 3  reversely connected in series, and the other of the two rectifier branches includes a second diode D 2  and a fourth diode D 4  reversely connected in series. The high voltage output terminal C of the AC-DC conversion circuit  28  is formed at a connection point of a cathode of the silicon control rectifier S 1  and a cathode of the silicon control rectifier S 3 , and the low voltage output terminal D of the AC-DC conversion circuit  28  is formed at a connection point of an anode of the second diode D 2  and an anode of the fourth diode D 4 . The output terminal C is connected to a positive power supply terminal of the position sensor  20 , and the output terminal D is connected to a negative power supply terminal of the position sensor  20 . The switch control circuit  30  includes a third resistor R 3 , an NPN transistor T 6 , and a fourth resistor R 4  and a fifth diode D 5  connected in series between the output terminal H 1  of the position sensor  20  and the control electrode G of the controllable bidirectional AC switch  26 . A cathode of the fifth diode D 5  is connected to the output terminal H 1  of the position sensor. One terminal of the third resistor R 3  is connected to the high voltage output terminal C of the AC-DC conversion circuit, and the other terminal of the third resistor R 3  is connected to the output terminal H 1  of the position sensor. A base of the NPN transistor T 6  is connected to the output terminal H 1  of the position sensor, an emitter of the NPN transistor T 6  is connected to an anode of the fifth diode D 5 , and a collector of the NPN transistor T 6  is connected to the high voltage output terminal C of the AC-DC conversion circuit. 
     In this embodiment, a reference voltage may be input to the cathodes of the two silicon control rectifiers S 1  and S 3  via a terminal SC 1 , and a control signal may be input to control terminals of S 1  and S 3  via a terminal SC 2 . The rectifiers S 1  and S 3  are switched on in a case that the control signal input from the terminal SC 2  is a high level, or are switched off in a case that the control signal input from the terminal SC 2  is a low level. Based on the configuration, the rectifiers S 1  and S 3  may be switched between a switch-on state and a switch-off state in a preset way by inputting the high level from the terminal SC 2  in a case that the drive circuit operates normally. The rectifiers S 1  and S 3  are switched off by changing the control signal input from the terminal SC 2  from the high level to the low level in a case that the drive circuit fails. In this case, the TRIAC  26 , the conversion circuit  28  and the position sensor  20  are switched off, to ensure the whole circuit to be in a zero-power state. 
       FIG. 10  shows a circuit diagram of a drive circuit  48  for a synchronous motor according to another embodiment of the present invention. The drive circuit  48  is similar to the drive circuit  46  in the previous embodiment and, the drive circuit  48  differs from the drive circuit  46  in that, the silicon control diodes S 1  and S 3  in the drive circuit  46  are replaced by general diodes D 1  and D 3  in the rectifier of the drive circuit  48 , and a zener diode Z 7  is connected between the two terminals C and D of the AC-DC conversion circuit  28 . In addition, in the drive circuit  48  according to the embodiment, a preset steering circuit  50  is disposed between the switch control circuit  30  and the TRIAC  26 . The preset steering circuit  50  includes a first jumper switch J 1 , a second jumper J 2  switch and an inverter NG connected in series with the second jumper switch J 2 . Similar to the drive circuit  46 , in this embodiment, the switch control circuit  30  includes the resistor R 3 , the resistor R 4 , the NPN transistor T 5  and the diode D 6 . One terminal of the resistor R 4  is connected to a connection point of an emitter of the transistor T 5  and an anode of the diode D 6 , and the other terminal of the resistor R 4  is connected to one terminal of the first jumper switch J 1 , and the other terminal of the first jumper switch J 1  is connected to the control electrode G of the TRIAC  26 , and the second jumper switch J 2  and the inverter NG connected in series are connected across two terminals of the first jumper switch J 1 . In this embodiment, when the first jumper switch J 1  is switched on and the second jumper switch J 2  is switched off, similar to the above embodiments, the rotor  14  still starts clockwise; when the second jumper switch J 2  is switched on and the first jumper switch J 1  is switched off, the rotor  14  starts counterclockwise. In this case, a starting direction of the rotor in the motor may be selected by selecting one of the two jumper switches to be switched on and the other to be switched off. Therefore, in a case that a driving motor is needed to be supplied for different applications having opposite rotational directions, it is just needed to select one of the two jumper switches J 1  and J 2  to be switched on and the other to be switched off, and no other changes need to be made to the drive circuit, hence, the drive circuit according to this embodiment has good versatility. 
     As discussed above, the position sensor  20  is configured for detecting the magnetic pole position of the permanent magnet rotor  14  of the synchronous motor  10  and outputting a corresponding signal. The output signal from the position sensor  20  represents some characteristics of the magnetic pole position such as the polarity of the magnetic field associated with the magnetic pole position of the permanent magnet rotor  14  of the synchronous motor  10 . The detected magnetic pole position is then used, by the switch control circuit  30 , control the controllable bidirectional AC switch  26  to be switched between a switch-on state and a switch-off state in a predetermined way, based on, together with the magnetic pole position of the permanent magnet rotor, the polarity information of the AC power supply  24  which may be obtained from the AC-DC conversion circuit  28 . It should be appreciated that the switch control circuit  30  and the position sensor  20  can be realized via magnetic sensing. Accordingly, the present teaching discloses a magnetic sensor for magnetic sensing and control of a motor according to the sensed information. 
     More details are disclosed below on the magnetic sensor that comprises aspects of both the position sensor  20  and the switch control circuit  30 . In describing the details of the magnetic sensor related to both the position sensor  20  and the switch control circuit  30 , the present teaching of this continuation-in-part application more focuses on various details related to the realization of the switch control circuit  30  via the magnetic sensor as disclosed herein. 
     The magnetic sensor according to the present teaching includes a magnetic field detecting circuit that can reliably detect a magnetic field and generate a magnetic induction signal indicative of certain characteristics of the magnetic field. The magnetic sensor as disclosed herein also includes an output control circuit that controls the magnetic sensor to operate in a state determined with respect to the polarity of the magnetic field as well as that of an AC power supply. As the magnetic sensor is coupled with the bidirectional AC switch  26 , the magnetic sensor can effectively regulate the operation of the motor via the bidirectional AC switch. Further, the magnetic sensor in the present teaching may be directly connected to a commercial/residential AC power supply with no need for any additional A/D converting equipment. In this way, the present disclosure of the magnetic sensor is suitable to be used in a wide range of applications. 
     Additional novel features associated with the magnetic sensor disclosed herein will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the accompanying drawings or may be learned by production or operation of the examples. The novel features of the present teachings on a magnetic sensor may be realized and attained by practice or use of various aspects of the methodologies, instrumentalities and combinations set forth in the detailed examples discussed below. The disclosed magnetic sensor, the signal processing method implemented in the magnetic sensor, and the electric motor incorporating the magnetic sensor and the signal processing method disclosed herein can be achieved realized based on any circuit technology known to one of ordinary skill in the art including but not limited to the integrated circuit and other circuit implementations. 
       FIG. 11  illustrates an exemplary diagram of a magnetic sensor  1105  according to an embodiment of the present teaching. The magnetic sensor  1105  includes a housing (not shown), a semiconductor substrate residing in the housing (not shown), a first input A 1   1102 , a second input A 2   1104 , an output port B  1106 , and an electronic circuit  1100  residing on the semiconductor substrate. The electronic circuit  1100  includes a control signal generation circuit  1110  and an output control circuit  1120  coupled to the control signal generation circuit  1110 . In an embodiment, the first input A 1   1102  and the second input A 2   1104  may be connected to an external power supply directly (e.g.,  1610  in  FIG. 16 ). In an embodiment, the first input A 1   1102  and the second input A 2   1104  may be connected in series to the external power supply through, e.g., an external load. 
     The control signal generation circuit  1110  may be configured to detect one or more signals, and generate a control signal based on the detected one or more signals. In some examples, the one or more signals may be one or more electrical signals received through electrical wires or cables. In some other examples, the one or more signals may be one or more magnetic signals or other types of signals received by the magnetic sensor  1105  wirelessly or by other means. 
     In operation, the control signal generation circuit  1110  determines, based on one or more detected signals, whether a predetermined condition is satisfied. If the predetermined condition based on the one or more detected signals, the control signal generation circuit  1110  may generate and transmit a first control signal to the output control circuit  1120  that will then accordingly control the magnetic sensor  1105  to operate in a first state. In the first state, an electrical (load) current may flow out of the magnetic sensor to the output port B  1106 . The control signal generation circuit  1110  may also generate and transmit a second control signal to the output control circuit  1120  to control the magnetic sensor  1105  to operate in a second state. In the second state, the electrical (load) current may flow from the output port B  1106  into the magnetic sensor. How to determine the first state or the second state at the control signal generation circuit is described in further details. 
     On the other hand, when it is determined that the predetermined condition is not satisfied based on the one or more detected signals, the control signal generation circuit  1110  may generate and transmit a third control signal to the output control circuit  1120  to control the magnetic sensor  1105  to operate in a third state. In the third state, no electrical (load) current flows through the output port B  1106 . In some situations in the third state, only a small amount of current flows through the output port B  1106 , e.g., the intensity of the current is less than one fourth of the electrical (load) current. 
     In some embodiment, the output control circuit  1120  is coupled with the control signal generation circuit  1110  and configured to control the magnetic sensor  1105  to operate in a state determined based on the control signal received from the control signal generation circuit  1110 . For example, when the output control circuit  1120  receives the first control signal, the output control circuit  1120  controls the magnetic sensor  1105  to operate in the first state in which the electrical (load) current flows out to the output port B  1106 . When the output control circuit  1120  receives the second control signal, the output control circuit  1120  controls the magnetic sensor  1105  to operate in the second state in which the electrical (load) current flows from outside into the magnetic sensor via the output port B  1106 . When the output control circuit  1120  receives the third control signal, the output control circuit  1120  controls the magnetic sensor  1105  to operate in the third state in which no electrical (load) current flows through the output port B  1106  (or only a small amount of current flows through when compared with the electrical (load) current, e.g., such a current is less than one fourth of the electrical (load) current). In an embodiment, the output control circuit  1120  may alternately receive a plurality of control signals, including the first control signal and the second control signal, etc. Accordingly, the output control circuit  1120  may control the magnetic sensor  1105  to operate alternately among different states. Specifically, the magnetic sensor  1150  may operate alternately between the first state and the second state. In an embodiment, when the magnetic sensor  1105  operates in the third state, the magnetic sensor  1105  may be prevented from operating in either the first state or the second state. 
     In an embodiment, when the first input A 1   1102  and the second input A 2   1104  are connected to the external AC power supply  1610  ( FIG. 16 ), the operating frequency of the magnetic sensor  1105 , whether in the first state, the second state, or the third state, may be set to be positively proportional to the frequency of the external AC power supply  1610 . In an embodiment, the operating frequency of the magnetic sensor  1105  in the third state is twice of the operating frequency of the first state or the second state, which is twice of the frequency of the external AC power supply  1610 . 
       FIG. 12  illustrates an exemplary diagram of the magnetic sensor  1105  according to a different embodiment of the present teaching. In this embodiment, the magnetic sensor  1105  comprises the first input A 1   1102 , the second input A 2   1104 , the output port B  1106 , and an electronic circuit  1100 . The electronic circuit  1100  comprises a magnetic field detecting circuit  1130 , a state control circuit  1140  coupled with the magnetic field detecting circuit  1130 , and the output control circuit  1120  coupled with the state control circuit  1140 . 
     The magnetic field detecting circuit  1130  may be configured to detect an external magnetic field and output a magnetic induction signal in accordance with the detected external magnetic field. The magnetic induction signal may indicate or represent the polarity and strength of the external magnetic field. 
     The state control circuit  1140  may be configured to determine whether the a predetermined condition is satisfied, and transmit a corresponding control signal to the output control circuit  1120  based on the determination upon receiving the control signal, the output control circuit  1120  may control the magnetic sensor  1105  to operate in a corresponding state determined based on the magnetic induction signal. Specifically, when the predetermined condition is satisfied, the corresponding state may be one of the first state and the second state, corresponding respectively to a specific polarity of the external magnetic field indicated by the magnetic induction signal. For example, the first state may correspond to a situation in which a first polarity of the external magnetic field is detected, and the second state may correspond to a situation in which a second polarity (which is opposite to the first polarity) of the external magnetic field is detected. Accordingly, when the predetermined condition is satisfied and the external magnetic field exhibits a first polarity, the state control circuit  1140  may transmit a control signal indicating as such to the output control circuit  1120 , according to which the output control circuit  1120  may control the magnetic sensor  1105  to operate in the first state. As described above, in the first state, the electrical (load) current flow from the magnetic sensor to outside via the output port B  1106 . When the predetermined condition is satisfied and the external magnetic field exhibits a second polarity that is opposite to the first polarity, the state control circuit  1140  may transmit a control signal indicating as such to the output control circuit  1120 , based on which the output control circuit  1120  may control the magnetic sensor  1105  to operate in the second state. As described above, in the second state, the electrical (load) current flows from outside into the magnetic sensor via the output port B  1106 . 
     On the other hand, when the state control circuit  1140  determines that the predetermined conditions is not satisfied (or when the state control circuit  1140  does not respond to the magnetic induction signal or cannot obtain the magnetic induction signal from the magnetic field detecting circuit  1130 ), the state control circuit  1120  may transmit a control signal indicating as such to output control circuit  1120  to control the magnetic sensor  1105  to operate in a third state. In the third state, no electrical (load) current flows through the output port B  1106  (or only a small amount of current flows through the output port B compared with the electrical (load) current, e.g., the intensity of the current is less than one fourth of the electrical (load) current). 
     The output control circuit  1120  is coupled with the control signal generation circuit  1110  and configured to control the magnetic sensor  1105  to operate in a state determined based on a control signal received from the control signal generation circuit  1110 . For example, when the output control circuit  1120  receives the control signal indicating that the predetermined condition is met and a first polarity of the external magnetic field, the output control circuit  1120  controls the magnetic sensor  1105  to operate in the first state, allowing the electrical (load) current flow out of the magnetic sensor via the output port B  1106 . When the output control circuit  1120  receives the control signal indicating satisfaction of the predetermined condition and a second polarity detected from the external magnetic field, the output control circuit  1120  controls the magnetic sensor  1105  to operate in the second state, allowing the electrical (load) current flow from outside into the magnetic sensor via output port B  1106 . When the output control circuit  1120  receives the control signal indicating that the predetermined condition is not met, the output control circuit  1120  controls the magnetic sensor  1105  to operate in the third state, in which no electrical (load) current may flow through the output port B  1106  (or only a small amount of current flows through the output port B compared with the electrical (load) current above, e.g., the current is less than one fourth of the electrical (load) current). In an embodiment, the output control circuit  1120  may receive alternately a plurality of the control signals in time. Accordingly, the output control circuit  1120  controls the magnetic sensor  1105  to operate among different states alternately, including between the first state and the second state. 
     In an embodiment, the output control circuit  1120  may be configured based on a user&#39;s specification. For example, the output control circuit  1120  may be configured to control the magnetic sensor  1105  to operate alternately between a working state and a high-impedance state. The working state may correspond to the first state or the second state, and the high-impedance state may correspond to the third state. 
       FIG. 13  illustrates an exemplary diagram of the magnetic sensor  1105  according to yet another embodiment of the present teaching. In this embodiment, an exemplary construction of the magnetic field detecting circuit  1130  is provided. The electronic circuit  1100 , similar to  FIG. 12 , includes the magnetic field detecting circuit  1130 , the state control circuit  1140 , and the output control circuit  1120 . The magnetic field detecting circuit  1130  in this embodiment comprises a magnetic sensing element  1131 , a signal processing element  1132 , and an analog-digital conversion element  1133 . 
     The magnetic sensing element  1131  may be configured to detect and output to the signal processing element an analog electrical signal that is indicative of certain information related to the external magnetic field. For example, the output of signal from the magnetic sensing element  1131  may indicate the polarity of the external magnetic field. In an embodiment, the magnetic sensing element  1131  may be implemented based on a Hall Board. 
     The signal processing element  1132  may be configured to process the analog electrical signal from the magnetic sensing element  1131  and generate a processed analog electrical signal by, e.g. amplifying and reducing the interference of the analog electrical signals in order to improve the accuracy of the detected signals. The processed analog electrical signal is sent to the analog-digital conversion element  1133 . 
     The analog-digital conversion element  1133  may be configured to convert the processed analog electrical signal to a magnetic induction signal. In situations where only the polarity of the external magnetic field needs to be detected, the magnetic induction signal may correspond to a switching digital signal. The state control circuit  1140  and the output control circuit  1120  in  FIG. 13  operate in the similar manner as disclosed with respect to  FIG. 12 . 
       FIG. 14  illustrates an exemplary implementation of the output control circuit  1120  according to an embodiment of the present teaching. In an embodiment, the output control circuit  1120  may be configured according to a user&#39;s specification. As shown in  FIG. 14 , the output control circuit  1120  includes a first switch K 1   1410 , a second switch K 2   1420 , and a third switch K 3   1430 . Each of the first switch K 1   1410 , the second switch K 2   1420 , and the third switch K 3   1430  is a diode or a transistor. The first switch is coupled with the output port B  1106  through the third switch K 3   1430  to form a first current path allowing the load current to flow through in a first direction. The second switch is coupled with the output port B  1106  through the third switch K 3   1430  to form a second current path allowing the load current to flow in a second direction opposite to the first direction. The first switch K 1   1410  and the second switch K 2   1420  respond to the magnetic induction signal  1405  to selectively turn on the corresponding current path. 
     In an embodiment, the first switch K 1   1410  and the second switch K 2   1420  may be selectively turned on or off according to a user&#39;s specification. In an embodiment, the first switch K 1   1410  and the second switch K 2   1420  may be configured to receive the magnetic induction signal  1405 , which indicates the detected polarity of the external magnetic field. The first switch K 1   1410  and the second switch K 2   1420  may be selectively turned on or off in response to the magnetic induction signal  1405 . For example, the first switch K 1   1410  may be a high-voltage conducting switch, and the second switch K 2   1420  may be a low-voltage conducting switch. To achieve that, the first switch K 1   1410  is connected to a higher voltage VDD  1407  (e.g., a direct current power supply), and the second switch K 2   1420  is connected to a lower voltage (e.g., ground). When the magnetic induction signal  1405  has a high voltage, e.g., indicating a first polarity detected from the external magnetic field, the first switch K 1   1410  may be turned on and the second switch K 2   1420  may be turned off. When the magnetic induction signal  1405  has a low voltage, e.g., indicating a second polarity, opposite to the first polarity of the external magnetic field, the first switch K 1   1410  may be turned off and the second switch K 2   1420  may be turned on. 
     In an embodiment, the third switch K 3   1430  may be turned on or off based on whether the magnetic sensor  1105  satisfies the predetermined condition. For example, when the magnetic sensor  1105  satisfies the predetermined condition, the third switch K 3   1430  may be turned on. Otherwise, the third switch K 3   1430  may be turned off. Details on how to control the third switch is discussed with respect to  FIG. 18 . 
     As described above, when the magnetic sensor  1105  satisfies the predetermined condition and the magnetic induction signal has a high voltage, the first switch K 1   1410  is turned on, the second switch K 2   1420  is turned off, and the third switch K 3   1430  is turned on. Accordingly, the first current path is on and the second current path is off. As a result, the output control circuit  1120  controls the magnetic sensor  1105  to operate in the first state. Namely, the electrical (load) current flows from the VDD  1407  through the first switch K 1   1410 , the third switch K 3   1430 , and finally out of the output port B  1106 . 
     When the magnetic sensor  1105  satisfies the predetermined condition and the magnetic induction signal has a low voltage, the first switch K 1   1410  is turned off, the second switch K 2   1420  is turned on, and the third switch K 3   1430  is turned on. Accordingly, the first current path is off and the second current path is on. As a result, the output control circuit  1120  may control the magnetic sensor  1105  to operate in the second state. Namely, the electrical (load) current flows into the output port B  1106 , through the third switch K 3   1430 , and the second switch K 2   1420 , to the ground. 
     When the magnetic sensor  1105  does not satisfies the predetermined condition, the third switch K 3   1430  is turned off. Accordingly, neither the first current path nor the second current path is on. As a result, the output control circuit  1120  may control the magnetic sensor  1105  to operate in the third state, no matter whether the magnetic induction signal  1405  has a high voltage or a low voltage. Namely, no electrical (load) current flows through the output port B  1106  (or only a small amount of current flows through the output port B compared with the electrical (load) current above, e.g., the current is less than one fourth of the electrical (load) current and cannot drive a load outside the magnetic sensor  1105 ). As such, the output control circuit  1120  does not respond to the magnetic induction signal  1405 . 
       FIG. 15  illustrates an exemplary implementation of the output control circuit  1120  according to another embodiment of the present teaching. As shown, the output control circuit  1120  is coupled with the magnetic field detecting circuit  1130 . The output control circuit  1120  receives the magnetic induction signal  1405  (as shown in  FIG. 14 ) from the magnetic field detecting circuit  1130 . The output control circuit  1120  includes a single-conducting switch D  1510 , a resistor R  1520 , and the third switch K 3   1430 . The single-conducting switch D  1510  is coupled with the output port B  1106  through the third switch K 3   1340 , forming a first current path allowing the load current to flow in a first direction. On the other hand, the resistor R  1520  is coupled with the output port B  1106  through the third switch K 3   1430 , forming a second current path allowing the load current to flow in a second direction opposite to the first direction. When the magnetic sensor  1105  satisfies the predetermined condition, the third switch K 3   1430  may be turned on. Otherwise, the third switch K 3   1530  may be turned off. Details on how to control the on/off of the third switch is discussed with respect to  FIG. 18 . The single-conducting switch D  1510  may be selectively turned on or off based on the magnetic induction signal  1405  received from the magnetic field detecting circuit  1130 . For example, when the magnetic induction signal  1405  has a high voltage, the single-conducting switch D  1510  is turned on. When the magnetic induction signal  1405  has a low voltage, the single-conducting switch D  1510  is turned off. In another embodiment, the resistor R  1520  may be replaced by another single-conducting switch connected anti-parallel with the single-conducting switch D  1510 . 
     As described above, when the magnetic sensor  1105  satisfies the predetermined condition and the magnetic induction signal  1405  received from the magnetic field detecting circuit  1130  has a high voltage, both the single-conducting switch D  1510  and the third switch K 3   1430  are turned on. Accordingly, the first current path is on and the second current path is off. As a result, the output control circuit  1120  may control the magnetic sensor  1105  to operate in the first state. Namely, the electrical (load) current flows out of the output port B  1106  through the single-conducting switch D  1510  and the third switch K 3   1530 . 
     When the magnetic sensor  1105  satisfies the predetermined condition and the magnetic induction signal  1405  received from the magnetic field detecting circuit  1130  has a low voltage, the single-conducting switch D  1510  is turned off and the third switch K 3   1430  is turned on. Accordingly, the first current path is off. As the magnetic induction signal is low, and the third switch K 3   1430  is on, the second current path is conducting. As a result, the output control circuit  1120  may control the magnetic sensor  1105  to operate in the second state. Namely, the electrical (load) current flows into the output port B  1106 , and through the third switch K 3   1530  and the resistor R  1520 , respectively. 
     When the magnetic sensor  1105  does not satisfies the predetermined condition, the third switch K 3   1430  is turned off. In this case, neither the first current path nor the second current path is on. As a result, the output control circuit  1120  may control the magnetic sensor  1105  to operate in the third state no matter whether the magnetic induction signal  1405  has a high voltage or a low voltage. Namely, no electrical (load) current flows through the output port B  1106 . As such, the output control circuit  1120  does not respond to the magnetic induction signal  1405 . 
       FIG. 16  illustrates another exemplary diagram of the magnetic sensor  1105  according to yet another embodiment of the present teaching. As shown, the input  1615  of the magnetic sensor  1105  is connected to an external AC power supply  1610 . In this embodiment, the magnetic sensor  1105  includes a rectifier  1150  connected to the input  1615  and configured to receive a pair of differential AC signals from the external AC power supply  1610  and convert the pair of differential AC signals to direct current (DC) signals. The output voltage of the rectifier  1150  may be used to power up the magnetic field detecting circuit  1130 , the state control circuit  1140 , and the output control circuit  1120 . The magnetic sensor  1105  may further comprise the magnetic detecting circuit  1130 , the state control circuit  1140 , and the output control circuit  1120 , as described above. 
       FIG. 17  illustrates an exemplary diagram of the rectifier  1150  according to an embodiment of the present teaching. The rectifier  1150  includes a full wave rectifier bridge and a stabilizing unit connected to the full wave rectifier. The full wave rectifier bridge includes a first diode D 1   1710 , a second diode D 2   1720 , a third diode D 3   1730 , and a fourth diode D 4   1740 . As shown in  FIG. 17 , the first diode D 1   1710  is connected in series to the second diode D 2   1720 , and the third diode D 3   1730  is connected in series to the fourth diode D 4   1740 . The output of the first diode D 1   1710  and the input of the second diode D 2   1720  are connected to the first input port VAC+  1705 , and the output of the third diode D 3   1730  and the input of the fourth diode D 4   1740  are connected to the second input port VAC−  1707 . In an embodiment, the first input port VAC+  1705  and the second input port VAC−  1707  are a pair of differential AC signals. The full wave rectifier bridge may be configured to convert the pair of differential AC signals outputted by the AC power supply  1610  to direct signals. The stabilizing unit may be a Zener diode DZ  1750  and configured to stabilize the direct signals outputted by the full wave rectifier bridge within a predetermined range. The stabilizing unit outputs a stabilized DC voltage. 
     In an embodiment, the input of the first diode D 1   1710  is connected to the input of the third diode D 3   1730  at a first connection point, thereby forming the grounded port of the full wave rectifier bridge. In addition, the output of the second diode D 2   1720  is connected to the output of the fourth diode D 4   1740  at a second connection point, thereby forming the output port of the full wave rectifier bridge, VDD  1760 . The Zener diode DZ  1750  is situated between the first connection point and the second connection point. In an embodiment, the output VDD  1760  may be connected directly with the output control circuit  1120 . 
     In an embodiment, the first input port VAC+  1705  and the second input port VAC−  1707  are connected to the external AC power supply  1610 . In this case, the output control circuit  1120  may respond to the polarity of the external AC power supply  1610  in addition to the magnetic induction signal  1405 . 
     In an embodiment, whether the magnetic sensor  1105  operates in the first state, the second state, or the third state, depends on whether the magnetic sensor  1105  satisfies the predetermined condition, which may be determined according to a user&#39;s specification. Accordingly, the output control circuit  1120  may control the magnetic sensor  1105  to operate in the first state that the electrical (load) current may flow out of the output port B  1106  or in the second state that the electrical (load) current may flow into the output port B  1106 . Alternatively or additionally, when the magnetic sensor  1105  satisfies the predetermined condition, the output control circuit  1120  may control the magnetic sensor  1105  to operate alternately between the first state and the second state in response to the polarity of the external AC power supply  1610  and the polarity of the magnetic field indicated by the magnetic induction signal  1405 . When the magnetic sensor  1105  does not satisfy the predetermined condition, the output control circuit  1120  may control the magnetic sensor  1105  to operate in the third state that no electrical (load) current may flow through the output port B  1106  or only a small amount of current flows through the output port B compared with the electrical (load) current above, e.g., the intensity of the current is less than one fourth of the electrical (load) current. 
     In an embodiment, when the magnetic sensor  1105  satisfies the predetermined condition, the output control circuit  1120  may respond to both the magnetic induction signal and the external AC power supply  1610  to further control the magnetic sensor  1105  to operate in the first state or the second state. For example, when the magnetic sensor  1105  satisfies the predetermined condition and the magnetic induction signal  1405  indicates that the external magnetic field has the first magnetic polarity and the external AC power supply  1610  has the first electric polarity, the output control circuit  1120  may control the magnetic sensor  1105  to operate in the first state. For another example, when the magnetic sensor  1105  satisfies the predetermined condition and the magnetic induction signal  1405  indicates that the external magnetic field has the second magnetic polarity which is opposite to the first magnetic polarity and the AC power supply  1610  has the second electric polarity which is opposite to the first electric polarity, the output control circuit  1120  may control the magnetic sensor  1105  to operate in the second state. 
       FIG. 18  illustrates an exemplary diagram of the magnetic sensor  1105  according to yet another embodiment of the present teaching. In this exemplary embodiment, an exemplary construction of the state control circuit  1140  is provided. As shown, the input  1615  of the magnetic sensor  1105  is connected to an external AC power supply  1610 . As shown before, the magnetic sensor  1105  includes a rectifier  1150  connected to the input  1615  and configured to receive a pair of differential AC signals from the external AC power supply  1610  and convert the pair of differential AC signals to direct current signals. The magnetic sensor  1105  further comprises the magnetic detecting circuit  1130 , the state control circuit  1140 , and the output control circuit  1120 . As shown in  FIG. 18 , the state control circuit  1140  further comprises a voltage detecting circuit  1142 , a delay circuit  1141 , and a logic circuit  1143 . 
     The voltage detecting circuit  1142  may be configured to detect whether a voltage in the magnetic sensor  1105  equals to or exceeds a threshold voltage. When the voltage exceeds the threshold voltage, the voltage detecting circuit  1142  generates a predetermined trigger signal and transmits it to the delay circuit  1141 . In an embodiment, the voltage may be the supply voltage of the magnetic field detecting circuit  1130 . The threshold voltage may be the minimal voltage required for the operation of the magnetic sensing element  1131 , the signal processing element  1132 , and the analog-digital conversion element  1133  of the magnetic field detecting circuit  1130 . In an embodiment, the threshold voltage may set to be a value that is smaller than the stabilized DC voltage achieved by the stabilizing unit as described with respect to  FIG. 17 . 
     Once being triggered by the voltage detecting circuit  1142 , the delay circuit  1141  determines whether the magnetic sensor  1105  satisfies the predetermined condition. Specifically, the delay circuit  1141  may start to time, upon the receipt of the predetermined trigger signal from the voltage detecting circuit  1142 . When the timed period is equal to or longer than a predetermined length of period, the delay circuit  1141  determines that the magnetic sensor  1105  satisfies the predetermined condition. Otherwise, the delay circuit  1141  determines that the magnetic sensor  1105  does not satisfy the predetermined condition. 
     The logic circuit  1143  may be configured to enable the output control circuit  1120  to respond to the magnetic induction signal and control the magnetic sensor  1105  to operate in any of the three states in the manner as discussed herein. For example, the magnetic sensor will operate in the first state or the second state when the timed period recorded by the delay circuit  1141  is equal to or greater than the predetermined period. The logic circuit  1143  is further configured to enable the output control circuit  1120  to control the magnetic sensor  1105  to operate in the third state when the timed period recorded by the delay circuit  1141  is less than the predetermined period. 
     In an embodiment, to detect that the supply voltage of the magnetic field detecting circuit  1130  reaches the predetermined voltage threshold is to ensure that all the modules of the magnetic field detecting circuit  1130 , i.e., the magnetic sensing element  1131 , the signal processing element  1132 , and the analog-digital conversion element  1133 , may function normally. 
       FIG. 19  illustrates an exemplary implementation circuit of a part of the magnetic sensor  1105  according to yet another embodiment of the present teaching. Specifically,  FIG. 19  illustrates an exemplary implementation of the output control circuit  1120  and the state control circuit  1140 . The state control circuit  1140  includes the voltage detecting circuit  1142 , the delay circuit  1141 , and the logic circuit  1143 , which is an AND gate  1910  as shown in  FIG. 19 . A first input of the AND gate  1910  may correspond to the magnetic induction signal  1905 , a second input of the AND gate  1910  may be connected to an output of the delay circuit  1141 , and the output of the AND gate  1910  may be connected to the output control circuit  1120 . 
     In this embodiment, the output control circuit  1120  includes three high-voltage conducting switches M 0   1920 , M 1   1960 , M 2   1970 , a diode D 5   1980 , an inverter  1990 , a first resistor R 1   1930 , and a second resistor R 2   1950 . The control terminal of the switch M 0   1920  is connected to the output of the AND gate  1910 . The input of the switch M 0   1920  is connected to a voltage output port  1940  (OUTAD+) of the rectifier  1150  through the resistor R 1   1930 . The switch M 2   1970  is coupled in parallel with the switch M 0   1920 . The control terminal of the switch M 2   1970  is connected to the output of the delay circuit  1141  through the inverter  1990 . In an embodiment, the equivalent resistance of the switch M 2   1970  is greater than that of the switch M 0   1920 . 
     In operation, when the timed period recorded by the delay circuit  1141  is equal to or longer than the predetermined threshold period, the delay circuit  1141  outputs a high voltage. Accordingly, this high voltage allows the magnetic induction signal  1905  from the magnetic field detecting circuit  1130  is transmitted to the switch M 0   1920  through the AND gate  1910 . In addition, when the signal from the AC power supply  1610  is in the positive half cycle and the magnetic induction signal  1905  from the magnetic field detecting circuit  1130  outputs low voltage, the switch M 0   1920  and the switch M 2   1970  may be turned off, and the switch M 1   1960  may be turned on. As a result, the electrical (load) current may flow out of the output port B  1106  through the switch M 1   1960 . Namely, the output control circuit  1120  operates the magnetic sensor  1105  in the first state. Alternatively, when the signal from the AC power supply  1610  is in the negative half cycle and the magnetic induction signal  1905  from the magnetic field detecting circuit  1130  outputs high voltage, the switch M 0   1920  may be turned on, and the switches M 1   1960  and M 2   1970  may be turned off. As a result, the electrical (load) current may flow into the output port B  1106  and pass through the diode D 5   1980  and the switch M 0   1920 . Namely, the output control circuit  1120  may control the magnetic sensor  1105  to operate in the second state. 
     When the timed period recorded by the delay circuit  1141  is shorter than the threshold period. The delay circuit  1141  and the AND gate  1910  may output a low voltage, the switches M 0   1920  and M 1  may be turned off, and the switch M 2   1970  may be turned on. As a result, the electrical current flows into the output port B  1106  and passes through the diode D 5   1980  and the switch M 2   1970 . Since the equivalent resistance of the switch M 2   1970  is large, the electrical current is very small, or negligible. That is, the output control circuit  1120  controls the magnetic sensor  1105  to operate in the third state. 
       FIG. 20  illustrates another embodiment of the output control circuit  1120  in connection with the state control circuit  1140 . The state control circuit  1140  includes the voltage detecting circuit  1142 , the delay circuit  1141 , and the logic circuit  1143 . Specifically, the logic circuit  1143  of the state control circuit  1140  includes a first signal input port  2002 , a second signal input port  2004 , a first signal output port  2006 , and a second signal output port  2008 . The first signal input port  2002  may be connected to the output of the delay circuit  1141 , and the second signal input port may be connected to receive the magnetic induction signal  2005 . When the timed period recorded by the delay circuit  1141  is shorter than the threshold period, the logic circuit  1143  may be configured to output a low voltage as the delay circuit  1141 . On the other hand, when the timed period recorded by the delay circuit  1141  is equal to or longer than the threshold period, the delay circuit  1141  may output high voltage. Further, the logic circuit  1143  may output the magnetic induction signal  2005  through the first signal output port  2006  or the second signal output port  2008 . The output signals in the first signal output port  2006  and the second signal output port  2008  may have a 180 degree phase difference. It should be appreciated that the output signals in the first output port  2006  and the second output port  2008  cannot have high voltages at the same time. 
     In this embodiment, the output control circuit  1120  includes three switches, i.e., switches M 3   2060 , M 4   2040 , and M 5   2070 , two resistances, i.e., resistances R 3   2050 , and R 4   2030 , and a protecting diode D 6   2020 . Specifically, the switches M 3   2060  and M 5   2070  are both high-voltage conducting switches, and the switch M 4   2040  is a low-voltage conducting switch. The control terminals of the switch M 3   2060  and the switch M 5   2070  are connected to the first signal output port  2006  and the second signal output port  2008  of the logic circuit  1143 , respectively. The input of the switch M 3   2060  is connected to a first port of the resistor R 3   2050 . The output of the switch M 3   2060  is connected to the grounded output (OUTAD−  2080 ) of the rectifier  1150  (as shown in  FIG. 15 ). 
     The control terminal of the switch M 4   2040  is connected to a second port of the resistor R 3   2050 . The input of the switch M 4   2040  is connected to the voltage output port (OUTAD+  2010 ) of the rectifier  1150 . The output of the switch M 4   2040  is connected to the input of the switch M 5   2070 . The output of the switch M 5   2070  is connected to the voltage output port (OUTAD−  2080 ) of the rectifier  1150 . In an embodiment, the voltage output port (OUTAD−  2080 ) is a floating ground. The output of the switch M 4   2040  is connected to the input of the switch M 5   2070  and the output port B  1106 . The control terminal of the switch M 4   2040  is connected to the positive polarity of the protecting diode D 6   2020 . The input of the switch M 4   2040  is connected to the negative polarity of the protecting diode D 6   2020 . The resistor R 4   2030  is connected between the control terminal and input terminal of the switch M 4   2040 . 
     In operation, when the timed period recorded by the delay circuit  1141  is equal to or longer than the threshold period, the delay circuit  1141  outputs a high voltage. In this case, the logic circuit  1143  allows the magnetic induction signal be output through the first signal output port  2006  or the second signal output port  2008 . The output signals in the first signal output port  2002  and the second signal output port  2004  may have a 180 degree phase difference. In addition, when the signal from the AC power supply  1610  is in the positive half cycle and the magnetic induction signal  2005  from the magnetic field detecting circuit  1130  corresponds to a high voltage, the switches M 3   2060  and M 4   2040  may be turned on, the switch M 5   2070  may be turned off. As a result, the electrical (load) current flows out of the output port B  1106  through the switch M 4   2040 . Namely, the output control circuit  1120  controls the magnetic sensor  1105  to operate in the first state. Alternatively, when the signal from the AC power supply  1610  is in the negative half cycle and the magnetic induction signal  2005  from the magnetic field detecting circuit  1130  corresponds to a low voltage, the switches M 3   2060  and M 4   2040  may be turned off, and the switch M 5   2070  may be turned on. As a result, the electrical current flows into the output port B  1106  and passes through the switch M 5   2070 . Namely, the output control circuit  1120  controls the magnetic sensor  1105  to operate in the second state. 
     When the timed period recorded by the delay circuit  1141  is shorter than the threshold period, the output control circuit  1120  is designated to control the magnetic sensor  1105  to operate in the third state. In this case, the delay circuit  1141  outputs a low voltage, the logic circuit  1143  outputs a low voltage at each of the first output port  2006  and the second output port  2008 , and the switches M 3   2060 , M 4   2040 , and M 5   2070  may be turned off. As a result, no electrical current flows through the output port B  1106  (or only a small amount of current flows through the output port B compared with the electrical (load) current above, e.g., the current is less than one fourth of the electrical (load) current). 
       FIG. 21  is a flowchart of an exemplary method of signal processing performed by the magnetic sensor  1105 , according to an embodiment of the present teaching. At step S 101 , an external magnetic field is detected. A magnetic induction signal may be indicative of the polarity and/or strength of the external magnetic field is generated. Specifically, at step S 101 , analog electrical signals associated with an external magnetic field and information associated therein are detected and outputted. In addition, the detected analog electrical signal may be processed by amplifying and reducing interference of the analog electrical signal. Further, the processed analog electrical signal may be converted to generate the magnetic induction signal. In some applications, the magnetic induction signal may be a switch digital signal that is indicative of the polarity of the external magnetic field. 
     At step S 102 , it is determined whether a predetermined condition is satisfied. The predetermined condition is related or assessed with respect to a specific voltage of the magnetic sensor. If the predetermined condition is met, the method proceeds to step S 103 . Otherwise, the method proceeds to step S 104 . Specifically, the predetermined condition may be set as a predetermined period that the voltage of the magnetic sensor reaches the predetermined voltage threshold. In an embodiment, whether the predetermined condition is satisfied may be determined based on the period of time during which the voltage of the magnetic sensor  1105  is equal to or above a predetermined voltage threshold. As discussed herein, to perform step S 102 , it is determined whether the voltage of the magnetic sensor  1105  reaches the predetermined voltage threshold. If so, the delay circuit  1141  starts to time. If the timed period reaches a predetermined length, it is determined that the predetermined condition is satisfied. Otherwise, it is determined that the predetermined condition is not satisfied. 
     At step S 103 , based on the magnetic induction signal, the magnetic sensor is controlled to operate in at least one of a first state and a second state. As discussed herein, in the first state, an electrical (load) current flows out of the output port B  1106 . In the second state, the electrical (load) current flows into the output port B  1106 . At step S 104 , the magnetic sensor is controlled to operate in a third state, in which the magnetic sensor  1105  operates in neither the first state nor the second state, i.e., no current (or negligible) flows through the output port B  1106 . 
       FIG. 22  illustrates an exemplary diagram of a motor assembly  2200  incorporating the magnetic sensor discussed herein, according to an embodiment of the present teaching. The motor assembly  2200  comprises a motor M  1202  coupled with an external AC power supply  1610 , a controllable bi-directional AC switch  1300  coupled in series with the motor M  1202 , and the magnetic sensor  1105 . The magnetic sensor  1105  resides close to the rotor of the motor  1202  in order to detect the variation of the magnetic field near the rotor. 
     In an embodiment, the magnetic sensor  1105  includes a first input  1102  coupled to the motor  1202 , a second input  1104  coupled to the external AC power supply  1610 , and the output  1106  coupled to a control terminal of the controllable bi-directional AC switch  1105 . 
     In an embodiment, the motor assembly  2200  may further comprise a voltage reducing circuit  1105 , configured to e.g., provide a reduced voltage obtained based on the AC power supply  1610 , to the magnetic sensor  1105 . In this embodiment, the first input  1102  of the magnetic sensor  1105  is instead coupled to the voltage reducing circuit  1200 . 
       FIG. 23  illustrates an exemplary diagram of a motor  2300  according to an embodiment of the present teaching. The motor  2300  may be similar to the motor  1202  in  FIG. 22 . In an embodiment, the motor  2300  is a synchronous motor including a stator and a rotor M 1  rotating around the stator. The stator includes a stator core M 2  and a single phase winding M 3  winding around the stator core M 2 . The stator core M 2  may include pure iron, cast iron, cast steel, electrical steel, silicon steel, or any other soft magnetic materials. The rotor M 1  includes a permanent magnet. When the stator winding M 3  is coupled in series with the AC power supply  1610 , the rotor M 1  may operate at a uniform speed of 60 f/p revolution/minute (rmp) in the stable phase, where f is the frequency of the AC power supply  1610 , and p is the number of pole pairs of the rotor M 1 . The stator core M 2  has two opposite polarities, either of which has a pole arc (e.g., M 4 , M 5 ). The outer surface of the rotor M 1  is opposite to the pole arc (e.g., M 4 , M 5 ), thereby forming a non-uniform gap between the outer surface and the pole arc. The pole arcs (e.g., M 4 , M 5 ) of the stator poles are embedded with concave grooves. The portion of the pole arc other than the concave groove has the same center axis as the rotor M 1 . 
     A non-uniform magnetic field may be formed in the above configuration, which ensures that the polar of the rotor M 1  is relative to the center axis of the stator pole with an angle when the rotor M 1  is static. The angle ensures an initial torque for the rotor M 1  every time the motor M is powered up under the influence of the magnetic sensor  1105 . The polar of the rotor M 1  may be the boundary between the opposite magnetic polarities of the rotor M 1 . The center axis of the stator may be a line passing through the centers of the poles of the stator. In an embodiment, both the stator and the rotor M 1  have two magnetic polarities. In an embodiment, the stator and the rotor M 1  may have a greater number of magnetic polarities, e.g., four or six magnetic polarities. 
     Returning to  FIG. 22 , when the magnetic sensor  1105  satisfies the predetermined condition, the magnetic sensor  1105  may operate in either the first state or the second state depending on the signal from the AC power supply  1610  and the polarity of the permanent magnetic rotor M 1 . Specifically, when the signal from the AC power supply  1610  is in the positive half cycle and the magnetic field detecting circuit  1130  detects that the permanent magnetic rotor M 1  has a first polarity, the output control circuit  1120  controls the magnetic sensor  1105  to operate in the first state. Namely, an electrical current may flow from the magnetic sensor  1105  to the controllable bi-directional AC switch  1300 . Alternatively, when the signal from the AC power supply  1610  is in the negative half cycle and the magnetic field detecting circuit  1130  detects that the permanent magnetic rotor M 1  has a second polarity that is opposite to the first polarity, the output control circuit  1120  controls the magnetic sensor  1105  to operate in the second state, in which, the electrical current may flow from the controllable bi-directional AC switch  1300  to the magnetic sensor  1105 . 
     When the magnetic sensor  1105  does not satisfy the predetermined condition, the magnetic sensor  1105  operates in the third state, in which, no electrical current flows between the controllable bi-directional AC switch  1300  and the magnetic sensor  1105  (or only a small amount of current flows between the controllable bi-directional AC switch  1300  and the magnetic sensor  1105 ). 
     In an embodiment, the magnetic sensor  1105  includes the rectifier  1150  as shown in  FIG. 17  and the output control circuit  1120  as shown in  FIG. 14 . As described above, in  FIG. 14 , the output control circuit  1120  includes the first switch K 1   1410  which is a high-voltage conducting switch, the second switch K 2   1420  which is a low-voltage conducting switch, and the third switch K 3   1430 . When the predetermined condition is met, the third switch K 3   1430  is turned on. In addition, when the signal from the AC power supply  1610  is in the positive half cycle and the magnetic induction signal is a high voltage, the first switch K 1   1410  is turned on and the second switch K 2   1420  is turned off. As a result, the magnetic sensor  1105  operates in the first state, in which, the electrical current flows from the AC power supply  1610 , through the motor M  1202 , voltage reducing circuit  1105 , the first input port of the magnetic sensor  1105 , the voltage output port of the second diode D 2  in the full wave rectifier bridge, the first switch K 1   1410  of the output control circuit  1120 , the output port B  1106 , then the controllable bi-directional AC switch  1105 , finally back to the AC power supply  1610 . Alternatively, when the signal from the AC power supply  1610  is in the negative half cycle and the magnetic induction signal is a low voltage, the first switch K 1   1410  is turned off and the second switch K 2   1420  is turned on. As a result, the magnetic sensor  1105  operates in the second state, in which, the electrical current flows from the AC power supply  1610 , through the controllable bi-directional AC switch  1105 , the output port B  1106 , the second switch K 2   1420 , the grounded port of the full wave rectifier bridge, the first diode D 1   1710 , the first input port of the magnetic sensor  1105 , the voltage reducing circuit  1105 , the motor  1202 , and finally back to the AC power supply  1610 . 
     When the signal from the AC power supply  1610  is in the positive half cycle and the magnetic field detecting circuit  1130  outputs a low voltage, or when the signal from the AC power supply  1610  is in the negative half cycle and the magnetic field detecting circuit  1130  outputs a high voltage, neither the first switch K 1   1410  nor the second switch K 2   1420  can be turned on. Therefore, the output control circuit  1120  operates the controllable bi-directional AC switch  1105  alternately between “ON” and “OFF” states in a predetermined manner. The output control circuit  1120  may further enable the magnetic sensor  1105  to control the way of powering up the stator winding M 3  based on the variation of the polarity of the AC power supply  1610  and the magnetic detection information, rendering the varying magnetic field generated by the stator to rotate along with the rotor in a single direction in accordance with the position of the magnetic field of the rotor. This enables that the rotor M 1  to rotate in the fixed direction every time the motor  1202  is powered up. 
     On the other hand, when the magnetic sensor  1105  does not satisfy the predetermined condition, the third switch K 3   1430  is turned off. As a result, the magnetic sensor  1105  operates in the third state, in which, no electrical current flows in the motor assembly  2200  (or only a small negligible amount of current flows in the motor assembly  2200 ) compared with the electrical current above, e.g., the intensity of the current is less than one fourth of the electrical current. 
       FIG. 24  illustrates the waveforms of an output voltage from an AC power supply  1610  and the rectifier bridge  1150 , respectively, according to an embodiment of the present teaching. Specifically, the upper portion of  FIG. 24  illustrates the waveform of the output voltage from the AC power supply  1610 , and the lower portion of  FIG. 24  illustrates the waveform of the output voltage of the rectifier bridge  1150 . As shown, the frequency of the output voltage of the rectifier bridge is twice of the frequency of the AC power supply  1610 . 
     When the waveform of the output voltage of the rectifier bridge  1150  rises, the output control circuit  1120  may operate in the third state before the output control circuit  1120  operates in the first state or the second state. Accordingly, when the waveform of the output voltage of the AC power supply  1610  is in the positive half cycle, the magnetic sensor  1105  may operate in the first state. When the waveform of the output voltage of the AC power supply  1610  is in the negative half cycle, the magnetic sensor  1105  may operate in the second state. Therefore, the operating frequency of the third state is positively proportional to the operating frequency of the first state or the second state, and is also proportional to the frequency of voltage of the AC power supply  1610 . In an embodiment, the operating frequency of the third state is twice of the operating frequency of the first state or the second state, which is twice of the frequency of the AC power supply  1610 . 
     It should be appreciated that the examples described above are for illustrative purpose. The present teaching is not intended to be limiting. The magnetic sensor  1105  may be used in applications other than the motor assembly  2200  as described above. 
     Returning to  FIG. 22 , in an embodiment, the motor  1202  and the controllable bi-directional AC switch  1300  may be coupled in series with each other and form a first branch. The series-connected voltage reducing circuit  1200  and the magnetic sensor  1105  form a second branch. The first branch is coupled in parallel with the second branch between two ends of the external AC power supply  1610 . 
     Those skilled in the art will recognize that the present teachings are amenable to a variety of modifications and/or enhancements. For example, although the implementation of various components described above may be embodied in a hardware device, it can also be implemented as a software only solution—e.g., an installation on an existing server. In addition, the units of the host and the client nodes as disclosed herein can be implemented as a firmware, firmware/software combination, firmware/hardware combination, or a hardware/firmware/software combination. 
     While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that the teachings may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all applications, modifications and variations that fall within the true scope of the present teachings.