Brushless DC motor drive apparatus

A brushless DC motor drive apparatus for driving a rotor includes a drive circuit rotating the rotor, a current shutdown and auto-restart circuit coupled to the drive circuit, and a DC voltage comparison circuit coupled to the current shutdown and auto-restart circuit. The current shutdown and auto-restart circuit detects blockage of the rotor via the DC voltage comparison circuit and shuts off the power to the drive circuit accordingly.

CROSS REFERENCE

This Non-provisional application claims priority under U.S.C.§ 119(a) on Patent Application No(s). 094102462 filed in Taiwan, Republic of China on Jan. 27, 2005, the entire contents of which are hereby incorporated by reference.

BACKGROUND

The disclosure relates in general to a brushless DC motor drive apparatus. In particular, the present disclosure relates to a brushless DC motor drive apparatus without Hall sensor, and providing functions of automatic power shutoff and restoration.

Among electronic device, it is common to include a cooling fan, to prevent overheating and resulting burnout. Upon overheating, the fan is normally initialized to lower the temperature, and dissipate excess heat from the system.

Conventionally, the fan is driven by a motor. A brushless DC motor (BLDC) is conventionally utilized, owing to easy maintenance, good controllability, and efficient performance. Not only in low power applications such as motors in hard drives and compact disk (CD) drives, but also in high power applications such as the motor apparatus in electric cars, brushless DC motors provide advantages such as high efficiency, stable rotation, high torsion, endurance, and easy maintenance.

FIG. 1shows a circuit schematic of a conventional brushless DC motor driver, in which a drive circuit100of brushless DC motor includes a first winding L1, a second winding L2, a capacitor C1, transistors Q1, Q2, Q3, Zener diodes ZD1, ZD2, ZD3, and resistors R1, R2, R3. The first winding L1may be a supplementary winding, and the second winding L2may be a power winding, both of which magnetically excite and drive the rotor to rotate, via the switching operation and alternated current directions of the drive circuit100.

First State

When a constant voltage source provides a current, the voltage potential at node “a” is high, and the voltage potential at node “b” is relatively low, across both ends of the first winding L1simultaneously. Low voltage potential results at the base of the transistor Q2, subsequently switched off, such that no current flows through the first winding L1.

Concurrently, the base of the transistor Q3is at a high voltage potential, such that the transistor Q3becomes conductive, a current passes through the transistor Q3from the second winding L2to ground. The second winding L2exerts control over a stator generating an induced magnetic field so as to drive the rotor to rotate at a predetermined angle via the induced magnetic field. For example, rotating 90° counterclockwise.

Second State

When the rotor reaches the predetermined angle, the first winding L1detects a state of power generation, and correspondingly generates a reverse inductive signal (e.g., reverse voltage), so that the voltage potential at node “a” is low, and the voltage potential at node “b” is relatively high. Positive voltage is applied to the base of the transistor Q2, in turn switching the transistor Q2on current through the resistor R2and the transistor Q2to ground. Thus, the base of the transistor Q3is brought to a low voltage potential, and the transistor Q3is switched off, such that there is no current through second winding L2. Though no magnetic field is induced across the stator the rotor continues rotating in the same direction, returning to the first operating condition subsequently, alternating between operating conditions.

However, the above-mentioned conventional drive circuit has several problems to resolve. When the fan is blocked by a foreign object such as an obstacle, the rotor is stopped immediately. In the absence of tangential magnetic force, the first winding L1becomes inactive. As the result, the transistor Q2remains off, with no current through the first winding L1. Because the conventional drive circuit does not have the function of cutting the power when the fan is blocked, a continuous current is provided through the second winding L2and the transistor Q3to ground. Heat generated at second winding L2causes possible damage to the brushless DC motor and the entire system.

In addition, the conventional circuit cannot spontaneously restart the circuit operation to drive the rotor even if the obstacle is removed. To restore circuit operation, it is necessary to disconnect the power supply then reconnect the brushless DC motor, which presents considerable inconvenience.

SUMMARY

Accordingly, an embodiment of the invention provides a brushless DC motor drive apparatus including a drive circuit, a current shutdown and auto-restart circuit, and a DC voltage comparison circuit. The drive circuit functions as rotating the rotor. The current shutdown and auto-restart circuit is coupled to the drive circuit, and the DC voltage comparison circuit is coupled to the current shutdown and auto-restart circuit. The current shutdown and auto-restart circuit detects blockage of the rotor via the DC voltage comparison circuit, and shuts off a power to the drive circuit accordingly.

The drive circuit includes a first winding, a second winding, a first transistor, and a second transistor. When the drive circuit is powered on and the second transistor is switched off, no current is generated through the first winding, the first transistor becomes conductive, and the first transistor to the ground, such that a magnetic field is induced to drive the rotor to rotate at a predetermined angle. After the rotor is rotated, the first winding generates a voltage, and the second transistor is conductive, the first transistor is switched off, and there is no current is generated through the second winding, whereby the rotor is driven to rotate by the first winding and the second winding which are subjected to a switching operation and alternated current directions of the drive circuit.

The current shutdown and auto-restart circuit further includes a drive IC, and is coupled to the DC voltage comparison circuit. A signal output from the DC voltage comparison circuit is compared in the drive IC, and then the drive IC output another signal to determine the state of the current shutdown and auto-restart circuit. When the rotor rotates normally, the current shutdown and auto-restart circuit does not affect the drive circuit, but the current shutdown and auto-restart circuit shuts off a power to the drive circuit, only in the event blockage of the rotor via the DC voltage comparison circuit.

Further, the current shutdown and auto-restart circuit further includes a third transistor, imposing no effect on the drive circuit when off, and turning on to shut off the power to the drive circuit, when first transistor is off, and no current is generated through the second winding.

Furthermore, the current shutdown and auto-restart circuit further includes a fourth transistor. The drive IC outputs a signal to determine the conduction of the fourth transistor. The fourth transistor is switched off to turn on the third transistor, whereby power to the drive circuit is shut off, and the fourth transistor is switched on to turn off the third transistor, with the power to the drive circuit is on. Also, the current shutdown and auto-restart circuit further includes a capacitor, providing voltage to turn on the fourth transistor when power to the drive circuit is shut off, to enable the drive circuit to rotate the rotor.

DETAILED DESCRIPTION

FIG. 2Ais a block diagram of a brushless DC motor drive apparatus of an embodiment in the present invention, including a current shutdown and auto-restart circuit210, and a DC voltage comparison circuit220. The current shutdown and auto-restart circuit210is electrically connected to the brushless DC motor drive apparatus200. Under normal operation, the brushless DC motor drive apparatus200drives the rotor of the motor magnetically. When the rotor is blocked by an obstacle and brought to a stop, the current shutdown and auto-restart circuit210recognizes the abnormal condition via the DC voltage comparison circuit220, and accordingly outputs a signal to the brushless DC motor drive apparatus200for a power shutoff. As the result, the active components and the windings in the brushless DC motor drive apparatus200are thus safeguarded from overheating and burnout. Further, Upon removal of the blockage, the current shutdown and auto-restart circuit210spontaneously triggers the brushless DC motor drive apparatus200to resume normal operation.

FIG. 2BandFIG. 2Care schematic diagrams of a brushless DC motor drive apparatus according to another. embodiment in the present invention. As shown inFIG. 2B, a brushless DC motor drive apparatus200, includes a drive circuit110, a current shutdown and auto-restart circuit210, and a DC voltage comparison circuit220. The drive circuit110may drive circuit as in conventional application, incorporate two windings for switching operation, driving a rot-or of the motor magnetically. The Current shutdown and auto-restart circuit210and the DC voltage comparison circuit220are included in conjunction with the drive circuit110, whereby providing the function of automatic power shutoff and restoration. The current shutdown and auto-restart circuit210is electrically coupled to the drive circuit110at a node “c”, so as to control connection and disconnection of power to the brushless DC motor drive apparatus200.

The implementation of the brushless DC motor drive apparatus200in embodiments of the present invention is not restricted to the drive circuit110inFIG. 2B. For example, the transistor Q1, and the Zener diodes ZD1and ZD2in the drive circuit110may alternatively be replaced with a single diode D1, whereby providing a constant bias voltage. The replacement may be demonstrated as the drive circuit120inFIG. 2C. Furthermore, the resistors R1, R2, R3are exercised in drive circuits110and120for voltage division, whereby achieving a desirable voltage in the drive circuit. Additionally, the number of the capacitor C1is not limited to one, the drive circuits110,120may includes multiple capacitors connected in series. This configuration presents more design flexibility, rendering capacitance easily adjustable to meet the specific requirements of the user, rather than employing a single capacitor with particular capacitance.

A brushless DC motor drive apparatus according to the invention is now disclosed in detail. Referring toFIG. 3, which is a circuit schematic diagram of a brushless DC motor drive apparatus without a Hall sensor, as another embodiment in the present invention. InFIG. 3, the brushless DC motor drive apparatus200includes a drive circuit230, a current shutdown and auto-restart circuit210, and a DC voltage comparison circuit220. The drive circuit230includes a first winding L1, a second winding L2, capacitors C1, C3, transistors. Q1, Q2, a diode D1; a Zener diode ZD1, and resistors R1, R2. The first winding L1may be a supplementary winding, and the second winding L2may be a power winding. Under normal operation, the motor rotor is driven to rotate by both windings which are subjected to a switching operation and alternated current directions of the drive circuit230.

The current shutdown and auto-restart circuit210includes a drive integrated circuit (drive IC)211, diodes D2, D3, transistors Q3, Q4, and a capacitor C2. The DC voltage comparison circuit220mainly includes resistors R1, R2, R3, R4. A constant voltage is maintained at node “d” between R3and R4; whereas node “e” between R1and R2conveys a non-constant voltage varying with the switching operation and alternated current directions of the brushless DC motor drive apparatus200.

The current shutdown and auto-restart circuit210is electrically connected to the drive circuit230by deploying node “c”, and employing the second and fourth pins of the drive IC211, to acquire voltages at nodes “d” and “e” for comparison. Depending on voltage at the node “e” is greater than the constant voltage at the node “d”, square wave signals are output to the diodes D2and D3through the eighth and seventh pins correspondingly.

It should be understood that the diodes D2, D3, and the resistor R8which are connected between the drive IC211and the transistor Q4may be eliminated or replaced with other components with the exact arrangement subject to the model of the drive IC and user requirements.

Under normal operations, square wave signals are output from the eighth and seventh pins alternately, as there is a voltage difference between the node “d” and the node “e”. Since the switching signals output from the eighth and seventh pins are complementary, the base of the transistor Q4remains at a high voltage potential, resulting in continuously current across the transistor Q4. As the transistor Q4conducts, current flows through the resistor R7and the transistor Q4to the ground, resulting in a low voltage potential at the base of the transistor Q3. Consequently, the transistor Q3is switched off and the current shutdown and auto startup circuit210is inactive. The first winding L1and the second winding L2continue to magnetically drive the rotor of the motor, due to the switching operation and the alternated current directions of the brushless DC motor drive apparatus200.

Once a constant voltage source generates current, a high voltage potential is established at node “a”, and a relative low voltage potential is at node “b”, across the ends of the first winding L1. The base of the transistor Q2is thus at low voltage potential and is switched off. There is no current through the first winding L1.

The base of the transistor Q1is at high voltage potential, and the transistor Q1is conductive, such that current from the second winding L2flows through the transistor Q1to the ground. The second winding L2therefore exerts control over a stator generating an induced magnetic field to rotate the rotor to a predetermined angle, such as rotating 90 degrees counterclockwise.

When the rotor rotates a predetermined angle, the first winding L1detects the power status and produces a reverse signal (e.g., reverse voltage). At this point, the voltage potential at node “a” is low, the voltage potential at node “b” is relatively high. The positive voltage generates a high voltage potential at the base of the transistor Q2, which becomes conductive, whereby current passes through the resistor R2and the transistor Q2to the ground, creating low voltage potential at the base of the transistor Q1. This results in the transistor Q1being switched off, such that no current is generated through the second winding L2. Concurrently, the induced magnetic field ceases, and the rotor continues rotating in the same direction.

If the fan is blocked by a foreign object such as an obstacle, the rotor may be stopped immediately, entering a pending state. Since there is no tangential magnetic field present, current direction at node “e” between the resistors R1and R2does not alternate, such that the eighth and seventh pins of the drive IC211output no square wave signals to the diode D2, D3. Meanwhile, the base of the transistor Q4remains at the state of low voltage potential, and the transistor Q4is switched off. The base of the transistor Q3is at the state of high voltage potential, and the transistor Q3is switched on. Current thus travels through the resistors R7, R9and the transistor Q3to the ground. The base of the transistor Q1is now at the state of low voltage potential, and the transistor Q1is off, whereby there is no current through the second winding L2. The current shutdown and auto-restart circuit210may accordingly detect the abnormal condition via the DC voltage comparison circuit220, and shut off the power to the drive circuit230. This may prohibit reduces likelihood of overheating and fire hazards to the second winding L2.

The drive IC211utilizes the capacitor C2to charge and discharge electricity automatically. The eighth and seventh pins of the drive IC211may generate a high voltage periodically, to return the transistor Q4to conductivity. Upon removal of the obstacle, the transistor Q3is switched off, and the transistor Q1is switched on. As the result, the drive circuit230resumes normal operation. If the blockage remains, the drive IC211generates the triggering signal periodically, whereby the current shutdown and auto-restart circuit210may shut off the power supply so as to protect the active components and the windings of the drive apparatus, which may be triggered automatically to rotate the motor back on operating state, when the obstacle is removed. The disclosed brushless DC motor drive apparatus200requires no shut down and restart of the power supply, enhancing convenience.

However, the disclosed brushless DC motor drive apparatus is not restricted to the above-mentioned embodiments, it may employ complementary metal oxide semiconductor (CMOS) devices rather than the switching transistors Q1, Q2, Q3, Q4. The number of the resistors and the capacitors is not limited, with modifications appropriate to use allowable. In addition, an output (O/P) node can be applied so as to provide identification of power status. For example, it may be electrically coupled to a display monitor (or a display screen) via the third pin of drive IC211, so that the power operating status can be shown by the display monitor. Furthermore, deployment of the drive IC is not restricted to any specific model, and nodes are not bound to output square wave signals via the eighth pin or the seventh pin alternately, as long as the drive IC accomplishes the functionality of the embodiments as disclosed.