Dual current-limiting circuit for DC brushless motor

1. Field of the Invention

The present invention is related to a dual current-limiting circuit for a dc brushless motor and more particularly to a current-limiting circuit for operating a dc brushless motor while locked or in a failure condition, and to utilizing a dual current-limiting method to tremendously reduce current passing through two ends of a coil, so as to limit current and provide a low voltage level which is adequate for restarting the motor when the failure condition is eliminated.

2. Description of the Related Art

When a motor is locked or motor speed is decreased due to dust and dirt, both the motor current passing through a coil and heat produced thereon may tremendously increase. The insulated cover of the coil is heated, thereby resulting in deterioration and cracking due to high temperature. In order to prevent great current from passing through the coil while the fan motor is locked or fails to operate in a normal manner, an auto restart function has been built in a drive circuit of the motor. When the fan motor is operated abnormally, the drive circuit generates time-intermittent signals to allow current passing through the coil short-term (a few seconds) for avoiding great current continuously passing therethrough. If abnormal operation of the fan motor cannot still be eliminated after the current continuously passes therethrough short-term, it interrupts the current to pause the operation. After interrupting a short-term currently supply, an auto restart circuit restarts the motor fan to allow current to pass through the coil.

The restart function of the fan motor is periodically repeated as long as abnormal operation is not eliminated. It is available only for low airflow or low power consumption fan motors since the restart function, which uses maximum current manner, may consume great pulse current for restarting.

FIG. 1 illustrates a schematic view of a conventional driver circuit for a single phase dc brushless motor.

Referring to FIG. 1, the driver circuit for the single phase dc brushless motor includes four transistors Q 1 , Q 2 , Q 3 , Q 4 , five resistors R 1 , R 2 , R 3 , R 4 , R 5 , a coil L 1 , a Hall element IC 1 , a driver element IC 2 , and a capacitor C 1 . The Hall element IC 1 is used for detecting changes in a permanent magnetic field of a rotor to thereby output a weaker Hall voltage. And then the driver circuit IC 2 magnifies the Hall voltage to further output alternative signals (square waveform) from two terminals O 1 and O 2 . The coil L 1 is alternatively actuated to change current direction, so as to rotate a rotor.

FIG. 2 illustrates a voltage diagram for time of the conventional driver circuit for the single phase dc brushless motor.

Referring to FIG. 2, the driver element IC 2 has a restart function. The restart function of the driver element IC 2 may be turned off when the motor is operated in a normal manner and turned on when the motor is operated in an abnormal manner, so as to allow a great current to pass through the coil L 1 for only a short-term (a few seconds). When the motor is restarted by means of the restart function of the driver element IC 2 , the motor is driven by maximum current and thus it is available only for a low airflow motor or low power consumption motor. By contrast, a high airflow motor or high power consumption motor operating abnormally may endure great currents of more than 10 amperes to form a high pulse which results in damage to the transistor of the electronic components. The transistor cannot endure a great current or high pulse even if the driver element allows great current to pass through the coil for only a short-term.

The present invention intends to provide a dual current-limiting circuit that instantly turns on a first switch of a first limiting circuit adapted to suppress a voltage signal output to a coil while inputting a great abnormal input current, and subsequently turn on a second switch of a second limiting circuit adapted to suppress current passing there through at a low voltage level which is inadequate to damage the driver circuit. The dual current-limiting circuit is used to prevent the electronic components from damage due to inputting great abnormal input current in such a way as to mitigate and overcome the above problem.

The primary objective of this invention is to provide a dual current limiting circuit for a dc brushless motor which instantly turns on a first switch of a first limiting circuit adapted to supply a first voltage signal to a coil while limiting a great abnormal input current, and subsequently turned on a second switch of a second limiting circuit adapted to also suppress current passing therethrough but at a low voltage level which is inadequate to damage the driver circuit and still adequate to restart the motor if the great abnormal input current is eliminated.

The secondary objective of this invention is to provide a dual current-limiting circuit for a dc brushless motor which is adapted to suppress great current while auto-restarting, so as to avoiding instant great current or high pulses from passing through a coil and thereby being available for a high airflow fan motor.

The present invention is a dual current-limiting circuit for a dc brushless motor. The dual current-limiting circuit includes an over current detective circuit, an operation detective circuit, and a current limiting circuit. The over-current detective circuit produces a voltage signal that is used to determine whether an over current has been input to the motor. The operation detective circuit also produces a voltage signal used to determine whether the motor is operating in a normal manner. The current-limiting circuit decides to turn on a first switch of a first current limiting circuit and to subsequently turn on a second switch of a second current-limiting circuit depending upon the two voltage signals. When the second switch is turned on, the current-limiting circuit is capable of suppressing current passing through a coil at low voltage level, which is inadequate to damage a driver circuit and still adequate to restart the motor if the great abnormal input current is eliminated.

Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description and the accompanying drawings.

The present invention will now be described in detail with reference to the accompanying drawings wherein:

FIG. 1 is a schematic view of a conventional driver circuit for a single phase dc brushless motor;

FIG. 2 is a voltage diagram for time of the conventional driver circuit for the single phase dc brushless motor;

FIG. 3 is a block diagram of a dual current-limiting circuit for a dc brushless motor in accordance with the present invention;

FIG. 4 is a block diagram of the dual current-limiting circuit for a dc brushless motor in accordance with the present invention;

FIG. 5 is voltage diagrams for time of the dual current-limiting circuit at selected reference points in FIG. 4 in accordance with the present invention; and

FIG. 6 is voltage diagrams for time of the dual current-limiting circuit at selected reference points in FIG. 4 in various situations in accordance with the present invention.

FIG. 3 illustrates a block diagram of a dual current-limiting circuit for a dc brushless motor in accordance with the present invention.

Referring initially to FIG. 3, the motor circuit mainly includes a driver circuit 10 and a dual current-limiting circuit 20 . The driver circuit 10 includes a Hall voltage amplifier circuit 11 , a phase inverter circuit 12 , and a motor coil driver circuit 13 . The Hall voltage amplifier circuit 11 is used to amplify weak Hall voltage and output to the phase inverter circuit 12 . The phase inverter circuit 12 inverts the phase of the amplified Hall voltage of the Hall voltage amplifier circuit 11 at 180° and then output to the motor coil driver circuit 13 , so as to alternatively actuating the coil to rotate a rotor. The dual current-limiting circuit 20 includes an over-current detective circuit 21 , an operation detective circuit 22 , and a current-limiting circuit 23 . The over-current detective circuit 21 comprises a resistor and produces a first voltage signal used to determine whether an over-current has been input to the motor. The operation detective circuit 22 retrieves the amplified Hall voltage of the Hall voltage amplifier circuit 11 whose rectifier/integral circuit produces a second voltage signal (high or low voltage level) that is used to determine whether the motor is operated in a normal manner. The current-limiting circuit 23 decides to turn on or off the current-limiting function depending upon the two voltage signals of the over-current detective circuit 21 and the operation detective circuit 22 to thereby control the driver circuit 10 of the phase inverter circuit 12 . Current passing through the driver circuit 12 is suppressed at a low voltage level which is inadequate to damage it. The current-limiting circuit 23 comprises a comparator used to operate the two voltage signals of the over-current detective circuit 21 and the operation detective circuit 22 and then subsequently decides to turn on or off the current-limiting function.

FIG. 4 illustrates a block diagram of the dual current-limiting circuit for a dc brushless motor in accordance with the present invention. Referring to FIG. 4, the Hall voltage amplifier circuit 11 comprises a Hall element IC 1 , three resistors R 1 , R 2 , R 3 , a capacitor C 2 , and two operational amplifiers OP 1 and OP 2 . The combination of the resistors R 1 and R 2 performs as a voltage drop circuit while the combination of the resistor R 3 and the capacitor C 2 forms a power supply circuit which is used to provide the operational amplifiers OP 1 and OP 2 with a stable low voltage level and low noise-voltage. The operational amplifiers OP 1 and OP 2 retrieve and amplify a weak Hall voltage and then output it to the phase inverter circuit 12 .

The phase inverter circuit 12 mainly includes two operational amplifiers OP 3 and ON whose negative input terminals (−) input signals from the Hall voltage amplifier circuit 11 and whose positive input terminals (+) input a reference voltage level for comparing therewith. For example, when the input terminals (−) of the operational amplifiers OP 3 and ON respectively input a high voltage level and a low voltage level, the voltage level of the input terminal (−) of the operational amplifier ON is higher than a voltage reference of the input terminal (+). At this time, an output terminal of the operational amplifier ON produces a low voltage level. Meanwhile, the voltage level of the input terminal (−) of the operational amplifier OP 3 is lower than a voltage reference of the input terminal (+) and an output terminal produces high voltage level. Consequently, the phase inverter circuit 12 inverts the input voltage level at 180° which further outputs to the motor coil driver circuit 13 . Accordingly, the phase inverter circuit 12 performs as a low output impedance circuit of the motor coil driver circuit 13 .

The motor coil driver circuit 13 includes four complementary bridge transistors Q 1 , Q 2 , Q 3 , Q 4 , and four diodes D 5 , D 6 , D 7 , D 8 connected between collectors and emitters of the associated transistors Q 1 , Q 2 , Q 3 , Q 4 which are used to absorb voltage of counter-electromotive pulse generated by alternatively actuating a coil L 1 . The transistors Q 1 and Q 2 are PNP transistors. A base of the transistor Q 1 is connected to the operational amplifier OP 3 through two resistors R 13 and R 14 while a base of the transistor Q 2 is connected to the operational amplifier ON through two resistors R 14 and R 18 . Output signals of the operational amplifiers OP 3 and ON are complementary to the control current of the coil L 1 . By contrast, the transistors Q 3 and Q 4 are NPN transistors. A base of the transistor Q 3 is connected to the operational amplifier OP 1 through two resistors R 15 and R 19 while a base of the transistor Q 4 connecting to the operational amplifier OP 1 through two resistors R 16 and R 20 . Output signals of the operational amplifiers OP 1 and OP 2 are complementary to the control current of the coil L 1 .

FIG. 5 illustrates voltage diagrams for time of the dual current-limiting circuit at selected reference points in FIG. 4 in accordance with the present invention. Referring to FIGS. 4 and 5, the selected reference points V 1 , V 2 , V 3 , V 4 are the bases of the transistors Q 1 , Q 2 , Q 3 , Q 4 . The two selected reference points Va and Vb represent two ends of the coil L 1 which produces alternative current to drive the motor.

FIG. 6 illustrates voltage diagrams for time of the dual current-limiting circuit at selected reference points in FIG. 4 in various situations in accordance with the present invention. Referring to FIG. 6, each waveform performed at selected reference points comprises normal and abnormal operations.

Referring again to FIG. 4, the over-current detective circuit 21 includes a series connected resistor R 21 connecting to the motor coil driver circuit 13 . When the current of the motor coil driver circuit 13 is passing through the resistor R 21 , it may increase the voltage drop and thereby determine a voltage level limiting value output to the current-limiting circuit 23 .

The operation detective circuit 22 includes a capacitor C 5 and a resistor R 9 combined to form a signal retrieving circuit connected to the 25 output terminal of the operational amplifier OP 2 , and a diode D 2 and resistor 10 combined to form a detective circuit which may rectify the output signal of the operational amplifier OP 2 to dc voltage. A transistor Q 5 and a resistor R 8 combine to form a signal amplifier circuit whose output signal is integrated by a resistor R 11 and a capacitor C 6 to form a constant dc voltage and then output to an input terminal of an operational amplifier OP 5 . During normal operation, the voltage of an input terminal (−) of the operational amplifier OP 5 is lower than a reference voltage level of an input terminal (+) and thus the output terminal of the operational amplifier OP 5 outputs a high voltage level as well as the operation detective circuit 22 outputs a high voltage level (normal signal) to the current-limiting circuit 23 . During abnormal operation, since no input signal results in cutting off the transistor Q 5 , the voltage of an input terminal (−) of the operational amplifier OP 5 is higher than the reference voltage level of the input terminal (+) and thus the output terminal of the operational amplifier OP 5 outputs low voltage level as well as the operation detective circuit 22 outputs high voltage level (abnormal signal) to the current-limiting circuit 23 .

The current-limiting circuit 23 includes two electronic switch elements D 3 and D 4 , an operational amplifier OP 6 , a Zener diode ZD 1 , four resistors R 24 , R 25 , R 26 , R 27 , and two capacitors C 7 and C 8 to form a reference voltage level circuit. An input terminal (+) of the operational terminal OP 6 is connected to the output of the operation detective circuit 22 while an input terminal (+) is connected to the output of the series connected resistor R 21 . The operational amplifier OP 6 operates the input signals and then outputs high or low voltage levels from its output terminal to control turning on or off the electronic switch elements D 3 and D 4 , thereby controlling the input terminals (−) of the operational amplifiers OP 3 and ON of the phase inverter circuit 12 . The resistor R 25 and the Zener diode ZD 1 of the current-limiting circuit 23 performs as a constant-voltage circuit, which supplies reference dc constant voltage level. Subsequently, the reference dc constant voltage level is divided by the resistors R 23 , R 24 , R 26 , R 27 to serve as a reference voltage level of an input terminal (+) of an operational amplifier OP 6 . The reference voltage level Vx of the input terminal (+) of the operational amplifier have two levels: 1. Normal operation voltage level Vx 1 and 2. Abnormal operation voltage level Vx 2 .

During normal operation, the operation detective circuit 22 outputs a high voltage level, which may produce a first voltage level Vx 1 at a selected reference point of the resistor R 27 after passing through the resistors R 24 and R 26 .

During abnormal operation, the operation detective circuit 22 outputs a low voltage level, which may produce a second voltage level Vx 2 at the selected reference point of the resistor R 27 after passing through a series parallel connection of the resistors R 23 , R 24 , R 26 , R 27 . As the electronic switch elements D 3 and D 4 are turned on, the input terminals (−) of the operational amplifiers OP 3 and OP 4 are controlled at a low voltage level and thus the output terminals thereof output a high level, thereby controlling to actuate the driver circuit 10 .

The first voltage level Vx 1 is higher than the second voltage level Vx 2 , which are adjustable according to motor features and the current-limiting voltage level. The current-limiting circuit 23 performs its dual current-limiting function depending upon the high and low voltage level as well as dual voltage level. In the first limit stage, as the dual current-limiting circuit initially detects a current on the coil L 1 exceeding maximum power consumption for normally operating the motor, the current passing through the coil L 1 is limited and subsequently it turns on the second stage based on the high voltage level. In the second limit stage, since the current of the coil L 1 is limited in the first stage, the coil L 1 is still maintained at a low voltage level. Once the abnormal operation is eliminated, it is detected instantly and restarts the motor for which the low voltage level is adequate and necessary.

Referring again to FIG. 6, during normal operation, the alternative square waveforms at the selected reference points Vs 1 and Vs 2 are complementary. Similarly, alternative square waveforms at the selected reference points Va and Vb are also complementary. At the selected reference point Vk of the over-current detective circuit 21 is a high voltage level waveform with negative pulse output to the current-limiting circuit 23 . The selected reference point Vn of the operation detective circuit 22 produces a low voltage level and retrieves an output signal of the operational amplifier OP 2 of the Hall voltage amplifier circuit 11 . The selected reference point Vf produces a high voltage level after the reference voltage level of the operation detective circuit 22 and low voltage level of the selected reference point Vn are operated in the operational amplifier OP 5 . At the selected reference point Vz, voltage is divided and then at the selected reference point Vx a high divided voltage adapted to be a reference level in the first limit stage is obtained for determining abnormal operation. As the voltage level at the selected reference point Vx is higher than that at the selected reference point Ve, the electronic switch elements D 3 and D 4 are turned off by reverse bias and thus the input signal of the input terminals (−) of the operational amplifiers OP 3 and ON are uninfluenced. Consequently, the over-current detective circuit 21 is turned off in the first limit stage when the motor is operated in a normal manner.

Referring again to FIGS. 4 and 6, during abnormal operation, when the current passing through the coil L 1 is increased tremendously, at the selected reference point the output voltage of the over-current detective circuit 21 is also increased tremendously. When the voltage level at the selected reference point Vk is higher than that at the selected reference point Vx, the over-current detective circuit 21 is turned on in the first stage. At this time, the current-limiting circuit 23 outputs a low voltage level to turn on the electronic switch elements D 3 and D 4 . Meanwhile, the Hall voltage amplifier circuit 11 outputs no signal to the operation detective circuit 22 and it turns off the transistor Q 5 . Voltage at the selected reference point Vk must be higher than that at the selected reference point Vx after the low voltage level of the operational amplifier OP 5 is output and divided at the selected reference point Vz to obtain a low voltage level at the selected reference point Vx. Consequently, the voltage level at the selected reference point Vx is adapted to be a reference voltage level in the second limit stage for determining whether to successively limit current and eliminate abnormal operation.

Referring again to FIGS. 4 and 6, when the resistor R 22 and the capacitor C 8 of the over-current detective circuit 21 are successively charged and discharged at the selected reference point Vk, the current-limiting circuit 23 produces an oscillating signal. The oscillating signal is output to the selected reference points Vs 1 and Vs 2 , thereby not only limiting the amplitude of vibration of the phase inverter circuit 12 but also outputting a small amplitude of the oscillating signal to the motor coil driver circuit 13 by means of an oscillating circuit which consists of the resistor R 6 and capacitor C 4 , the resistor R 7 and capacitor C 3 , the resistor R 22 , and a capacitor C 8 . Consequently, an average restart current for the coil L 1 is produced.

Although the invention has been described in details with references to its presently preferred embodiment, it will be understood by one of ordinary skill in the art that various modifications can be made without departing from the spirit and the scope of the invention, as set forth in the appended claims.