BACKGROUND
1. Technical Field
The exemplary disclosure generally relates to motor control circuits and keyboards; and particularly to a motor control circuit for controlling rotational direction of a motor, and a keyboard assembly having the motor control circuit.
2. Description of Related Art
Computer keyboards are usually exposed to environmental contaminants, and are easily polluted by dust or other particles. A dust-proof keyboard may include a spindle, a flexible lid scrolled about the spindle, a motor for driving the spindle to rotate, and a button electronically connected to the motor. When the button is pressed, the motor drives the spindle to rotate to lay the flexible lid on the keyboard, whereby the flexible lid covers the keyboard to prevent the keyboard from being contaminated.
However, because the motor is controlled by the button, if a user forgets to press the button after using the keyboard, the keyboard is not covered by the flexible lid.
Therefore, there is room for improvement within the art.
BRIEF DESCRIPTION OF THE DRAWINGS
Many aspects of the embodiments can be better understood with reference to the drawings. In the drawings, the emphasis is placed upon clearly illustrating the principles of the disclosure.
FIG. 1 is a block diagram of a keyboard assembly according to an exemplary embodiment, the keyboard assembly including a motor control circuit and a motor.
FIG. 2 is essentially a circuit diagram of the motor control circuit and motor shown in FIG. 1.
FIG. 3 is a circuit diagram of a charging unit, a primary power supply and a backup power supply of the motor control circuit shown in FIG. 1.
DETAILED DESCRIPTION
FIG. 1 is a block diagram of a keyboard assembly having a motor control circuit, according to an exemplary embodiment. The keyboard assembly 300 can be used in conjunction with a computer for example. The keyboard assembly 300 includes the motor control circuit 100, a motor 200, a keyboard 310, and a flexible lid 330 driven by the motor 200. The keyboard 310 has a plurality of keys arranged thereon. The motor control circuit 100 can control the motor 200 to rotate clockwise or counterclockwise. The flexible lid 330 is withdrawn to expose the keyboard 310 when the motor 200 rotates in a first direction, e.g. in the clockwise direction, under the control of the motor control circuit 100. The flexible lid 330 is moved to cover a top surface of the keyboard 310 when the motor 200 rotates in a second direction reverse to the first direction, e.g. in the counterclockwise direction, under the control of the motor control circuit 100. In the exemplary embodiment, the motor 200 is an electro-mechanical servo motor.
The motor control circuit 100 according to an exemplary embodiment includes a controller 10, a primary power supply 20, a backup power supply 30, a voltage monitor unit 40, a power switching unit 50, a charging unit 60, and a motor driving chip 70. The voltage monitor unit 40 determines a working state of the primary power supply 20 according to an output voltage V1 (shown in FIG. 2) of the primary power supply 20, and outputs a state signal ST (shown in FIG. 2). The controller 10 controls the motor to rotate clockwise or counterclockwise according to the state signal ST. The primary power supply 20 constantly charges the backup power supply 30 via the charging unit 60 when the primary power supply 20 is in service. The power switching unit 50 switches on the backup power supply 30 to power the controller 10 and the motor 200 as a substitute for the primary power supply 20 when the output voltage V1 of the primary power supply 20 is lower than a predetermined threshold voltage.
FIG. 2 is a circuit diagram of the motor control circuit 100 and motor 200. The controller 10 has a state signal input pin P1, a first controlling pin P2, a second controlling pin P3, and a power pin VDD. The state signal input pin P1 receives the state signal ST outputted from the voltage monitor unit 40. Both of the first and second controlling pins P2 and P3 are electronically connected to the motor driving chip 70, to transmit a first controlling signal PWM1 and a second controlling signal PWM2 respectively to the motor driving chip 70. In one embodiment, the first and second controlling signals PWM1, PWM2 are in antiphase.
In the exemplary embodiment, the output voltage V1 of the primary power supply 20 is supplied by a power supply unit of a computer through a power supply pin VCC of a Universal Serial Bus (USB) connector J1 of the keyboard 310. Hence the primary power supply 20 seen in FIG. 1 is shown as the USB connector J1 in FIG. 2. The USB connector J1 is connected to another USB connector (not shown) of the computer. When the computer is powered on, the output voltage V1 is +5 volts; and when the computer is powered off, the output voltage V1 decreases gradually to 0 volts.
The backup power supply 30 is preferably a rechargeable battery pack, such as a supercapacitor or a nickel-hydrogen battery. In the exemplary embodiment, the backup power supply 30 is a supercapacitor which has a rated output voltage labeled as V2 in FIG. 2.
The voltage monitor unit 40 includes a voltage monitor chip 41 and a Schottky diode 43. The voltage monitor chip 41 has a voltage input pin VCC, a detecting pin SENSE, a first output pin RESET, and a second output pin RESET. The voltage input pin VCC is electronically connectable to either the primary power supply 20 or the backup power supply 30. In the exemplary embodiment, the voltage input pin VCC is electronically connected to the primary power supply 20 and to the backup power supply 30 via the Schottky diode 43. The detecting pin SENSE is electronically connected to the primary power supply 20 via a first current limiting resistor R1. The first output pin RESET is electronically connected to the Schottky diode 43 via a pull-up resistor R2, and is electronically connected to the state signal input pin P1 of the controller 10. The first output pin RESET is configured for outputting the state signal ST arising from a comparison between the output voltage V1 and the predetermined threshold voltage stored in the voltage monitor chip 41. When the output voltage V1 of the primary power supply 20 is higher than the predetermined threshold voltage, the first output pin RESET outputs the state signal ST as a high level signal (e.g. logic 1), and the second output pin RESET outputs a low level signal (e.g. logic 0). When the computer is powered off, the output voltage V1 of the primary power supply 20 decreases gradually until it is lower than the predetermined threshold voltage, then the first output pin RESET outputs a low level signal as the state signal ST, and the second output pin RESET outputs a high level signal.
In one embodiment, the value of the predetermined threshold voltage is 4.25V, and the voltage monitor chip 41 is a TL7733BIDR type made by Texas Instruments (TI). The Schottky diode 43 is a BAT54C type made by STMicroelectronics (ST). The Schottky diode 43 has two input terminals, A1 and A2, and an output terminal C. The input terminals A1 and A2 are electronically connected to the primary power supply 20 and to the backup power supply 30 respectively. The output terminal C is electronically connected to the voltage input pin VCC, and is also electronically connected to the first output pin RESET via the pull-up resistor R2. The primary power supply 20 powers the voltage monitor chip 41 via the Schottky diode 43 when the computer is working, and the backup power supply 30 powers the voltage monitor chip 41 via the Schottky diode 43 after the computer has been shut down.
The power switching unit 50 includes a switching chip 51, a light emitting diode (LED) D1, an N-channel metal-oxide-semiconductor field-effect transistor (MOSFET) Q1, and a second current limiting resistor R3. The switching chip 51 has a first power input pin INA electronically connected to the backup power supply 30, a second power input pin INB electronically connected to the primary power supply 20, a first enable pin ENBA electronically connected to the first output pin RESET, a second enable pin ENBB, a first power output pin OUTA, and a second power output pin OUTB electronically connected to the first power output pin OUTA. A node between the first and second power output pins OUTA and OUTB is electronically connected to the motor 200 and the power pin VDD of the controller 10, and the node outputs a power voltage labeled as V3 in FIG. 2 to the motor 200 and the power pin VDD of the controller 10.
The first enable pin ENBA is configured for controlling an electronic connection between the first power input pin INA and the first power output pin OUTA. When the first enable pin ENBA is activated by the voltage monitor chip 41, that is, when the voltage monitor chip 41 outputs a low level signal as the state signal ST to the first enable pin ENBA via the first output pin RESET, the first power input pin INA is electronically connected to the first power output pin OUTA to construct a current path. The second enable pin ENBB is configured for controlling an electronic connection between the second power input pin INB and the second power output pin OUTB, and is activated by a low level signal.
An anode of the LED D1 is electronically connected to the node between the first and second power output pins OUTA and OUTB via the second current limiting resistor R3, and a cathode of the LED D1 is electronically connected to a drain D of the N-channel MOSFET Q1. A source S of the N-channel MOSFET Q1 is grounded, and a gate G of the N-channel MOSFET Q1 is electronically connected to the first output pin RESET.
When the computer is working, the primary power supply 20 is in service, and the first and second output pins RESET and RESET of the voltage monitor chip 41 output a high level signal and a low level signal respectively. The second enable pin ENBB is activated, and thus the primary power supply 20 is able to power the controller 10 and the motor 200. In addition, the N-channel MOSFET Q1 is turned on, and thus the LED D1 is illuminated. When the computer is shut down, the primary power supply 20 goes out of service, and the output voltage V1 decreases to the predetermined threshold voltage. Thereupon the first and second output pins RESET and RESET of the voltage monitor chip 41 output a low level signal and a high level signal respectively, so the first enable pin ENBA is activated and thus the backup power supply 30 is able to power the controller 10 and the motor 200. Further, the N-channel MOSFET Q1 is turned off, and the LED D1 is also turned off.
FIG. 3 is a circuit diagram of the charging unit 60, the primary power supply 20 and the backup power supply 30 of the motor control circuit 100. The charging unit 60 includes a charging chip 61 and a voltage dividing circuit 63. The charging chip 61 has a power input pin VIN electronically connected to the primary power supply 20, a charging pin COUT electronically connected to the backup power supply 30, and an enable pin SHDN. The voltage dividing circuit 63 includes a first voltage dividing resistor R4 and a second voltage dividing resistor R5, which are connected in series between the primary power supply 20 and ground. The enable pin SHDN is electronically connected to a node between the first and second voltage dividing resistors R1 and R2. The enable pin SHDN is activated when the primary power supply 20 is in service, during which time the charging chip 61 converts a source current of the primary power supply 20 into a charging current, which is then forwarded to the backup power supply 30 (e.g. a supercapacitor).
Referring again to FIG. 2, the motor driving chip 70 has a first signal input terminal I1 electronically connected to the first controlling pin P2, a second signal input terminal I2 electronically connected to the second controlling pin P3, a first signal output terminal O1 corresponding to the first signal input terminal I1, and a second signal output terminal O2 corresponding to the second signal input terminal I2. Both of the first and second signal output terminals O1 and O2 are electronically connected to the motor 200. When the primary power supply 20 is in service, the state signal ST outputted from the voltage monitor chip 41 is a high level signal, the first controlling signal PWM1 outputted from the controller 10 to the motor driving chip 70 is a first level signal (such as a high level signal), and the second controlling signal PWM2 outputted from the controller 10 to the motor driving chip 70 is a second level signal (such as a low level signal), and this signaling arrangement causes the motor driving chip 70 to drive the motor 200 clockwise. Alternatively, when the primary power supply 20 goes out of service, the output voltage V1 becomes lower than the predetermined threshold voltage. Accordingly, the state signal ST outputted from the voltage monitor chip 41 is a low level signal, the first controlling signal PWM1 outputted from the controller 10 to the motor driving chip 70 is the second level signal (a low level signal), and the second controlling signal PWM2 outputted from the controller 10 to the motor driving chip 70 is the first level signal (a high level signal). This signaling arrangement causes the motor driving chip 70 to drive the motor 200 counterclockwise.
In typical use of the keyboard assembly 300, the keyboard 310 is electronically connected to a computer via the USB connector J1. When the computer is working, the voltage output from the power pin VCC of the USB connector J1 is 5 volts, that is, the primary power supply 20 is in service. The charging unit 60 charges the backup power supply 20. Simultaneously, the first output pin RESET of the voltage monitor chip 41 outputs a high level signal, the power switching unit 50 connects the primary power supply 20 to the controller 10 and the motor 200, and the controller 10 causes the motor driving chip 70 to drive the motor 200 clockwise, to cause the flexible lid 330 to withdraw or to be kept withdrawn so as to expose the keyboard 310. When the computer is shut down, the voltage of the power pin VCC of the USB connector J1 decreases gradually, that is, the output voltage V1 of the primary power supply 20 decreases gradually. When the output voltage V1 is lower than the predetermined threshold voltage, the first output pin RESET of the voltage monitor chip 41 outputs a low level signal, the power switching unit 50 connects the backup power supply 30 to the controller 10 and the motor 200, and the controller 10 causes the motor driving chip 70 to drive the motor 200 counterclockwise, to pull and extend the flexible lid 330 over the keyboard 310 to protect it.
The voltage monitor unit 40 detects the working state of the primary power supply 20, and outputs a state signal ST to the controller 10. The controller 10 controls the motor driving chip 70 to drive the motor 200 clockwise when the primary power supply 20 is in service, thereby driving the flexible lid 330 to be withdrawn to expose the keyboard 310. When the primary power supply 20 is out of service, the controller 10 controls the motor driving chip 70 to drive the motor 200 counterclockwise, thereby pulling and extending the flexible lid 330 to cover the keyboard 310. The motor control circuit 100 can control the rotation direction of the motor 200 according to the working state of the computer, so that when the computer is shut down the flexible lid 330 is automatically drawn across the keyboard 310.
The exemplary embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments.
Patent Application
20130139975
