Patent Application
20110163684
This application claims the priority benefit of Taiwan application serial no. 99100022, filed on Jan. 4, 2010. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of specification.
1. Field of the Application
The present application relates to a driving circuit of light emitting diodes. More particularly, the present application relates to a driving circuit capable of mitigating a flash phenomenon of light emitting diodes.
2. Description of Related Art
Light emitting diodes (LEDs) have features of small-size, power-saving and high durability, and as fabrication processes thereof become mature, price of the LEDs decreases, so that products using the LEDs as light sources are popular in recent years. Along with a general trend of energy-saving and carbon-reducing, the LED gradually becomes a new generation light source. Since the LED has a low operation voltage and is capable of actively emitting light with a certain brightness, wherein the brightness thereof can be adjusted by voltage or current, and meanwhile the LED has features of impact resistance, anti-vibration and long lifespan (100,000 hours), the LED is widely used in various terminal equipments, such as vehicle headlamps, traffic lights, text displays, billboards and large screen video displays, and domains such as general level architectural lighting and liquid crystal display (LCD) backlight, etc.
A conventional lamp can be dimmed through a triac dimmer, and the triac dimmer and the lamp used in a house can be separately set, for example, the triac dimmer can be set on a wall, so that a user can conveniently adjust a light intensity. Since the triac dimmer is only suitable for adjusting a resistive lamp, and is not suitable for directly adjusting the brightness of the LED, when an LED lamp is used to directly replace the conventional lamp, a flash phenomenon is generated due to different driving methods of the conventional lamp and the LED lamp.
The present application is directed to a driving circuit of light-emitting diodes (LEDs), in which a triangle waveform is compared with a waveform of an output voltage of a triac dimmer to deduce a conducting condition (i.e. a delay angle) of the triac dimmer, and then a corresponding pulse width modulation (PWM) signal is selected to drive a voltage converter circuit, so as to drive the LEDs. In this way, voltages of the LEDs can be accurately adjusted, so as to control currents of the LEDs, and since a brightness of the LED is controlled by the current, the converted PWM signal can mitigate a problem that a conventional analog circuit cannot accurately adjust the currents of the LEDs.
Accordingly, the present application provides a driving circuit of light emitting diodes (LEDs), which is adapted to receive an alternating current (AC) power adjusted by a triac dimmer to drive an LED unit. The driving circuit includes a rectifier unit, an isolation element, a processing unit and a voltage converter circuit. The rectifier unit rectifies the AC power to output a first operation voltage. The isolation element is coupled to the rectifier unit, and is used for receiving the first operation voltage to output a second operation voltage. The processing unit is coupled to the rectifier unit, and detects a conducting condition of the triac dimmer according to a voltage waveform of the first operation voltage and outputs a pulse width modulation (PWM) signal according to the conducting condition. The voltage converter circuit is coupled to the isolation element and the processing unit, and converts the second operation voltage into a driving voltage according to the PWM signal, so as to drive the LED unit.
In an embodiment of the present application, the isolation element is a diode, wherein an anode of the diode is coupled to the rectifier unit, and a cathode of the diode is coupled to the voltage converter circuit. The isolation element can also be a direct current (DC) transformer. The driving circuit further includes a capacitor coupled between a common node of the isolation element and the voltage converter circuit and the ground.
In an embodiment of the present application, the processing unit includes a comparator, a determining unit and a pulse width modulator. A positive input terminal of the comparator is coupled to the first operation voltage, and a negative input terminal of the comparator is coupled to a signal source. The determining unit is coupled to an output terminal of the comparator, and determines the conducting condition of the triac dimmer according to an output of the comparator. The pulse width modulator is coupled to the determining unit, and is used for outputting the PWM signal. The determining unit adjusts a duty cycle of the PWM signal according to the conducting condition and a look-up table. The look-up table records a corresponding relationship between the conducting condition of the triac dimmer and the duty cycle of the PWM signal. The signal source is, for example, a triangle wave signal source or a DC reference voltage.
In an embodiment of the present application, the rectifier unit is a bridge rectifier, and the processing unit can be implemented by an application-specific integrated circuit (ASIC). The triac dimmer is a tri-electrode AC switch (TRIAC), and the voltage converter circuit is a buck circuit.
The present application further provides a lighting apparatus, which is adapted to receive an AC power adjusted by a triac dimmer for lighting. The lighting apparatus includes an LED unit and a driving circuit. The driving circuit is coupled to the triac dimmer and the LED unit, and includes a rectifier unit, an isolation element, a processing unit and a voltage converter circuit. The rectifier unit rectifies the AC power to output a first operation voltage. The isolation element is coupled to the rectifier unit, and is used for receiving the first operation voltage to output a second operation voltage. The processing unit is coupled to the rectifier unit, and detects a conducting condition of the triac dimmer according to a voltage waveform of the first operation voltage and outputs a pulse width modulation (PWM) signal according to the conducting condition. The voltage converter circuit is coupled to the isolation element and the processing unit, and converts the second operation voltage into a driving voltage according to the PWM signal, so as to drive the LED unit.
According to the above descriptions, in the present application, the waveform of the output voltage of the triac dimmer is used to detect a delay angle of the triac dimmer, so as to adjust the PWM signal used for adjusting a brightness of the LEDs, so that the LEDs can obtain a stable PWM signal to avoid a flash problem.
In order to make the aforementioned and other features and advantages of the present application comprehensible, several exemplary embodiments accompanied with figures are described in detail below.
The accompanying drawings are included to provide a further understanding of the application, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.
Referring to
The driving circuit 102 mainly includes a rectifier unit 120, an isolation element 122, a processing unit 130 and a voltage converter circuit 140. The rectifier unit 120 is coupled to the triac dimmer 110, the isolation element 122 and the processing unit 130. The voltage converter circuit 140 is coupled to the isolation element 122, the processing unit 130 and the LED unit 150. The rectifier unit 120 is, for example, a bridge rectifier, and is used for rectifying the AC power AC1 to output a first operation voltage FV to the isolation element 122 and the processing unit 130. The isolation element 122 is, for example, a diode 125, wherein an anode of the diode 125 is coupled to the rectifier unit 120, and a cathode of the diode 125 is coupled to the voltage converter circuit 140. The diode 125 receives the first operation voltage FV and output a second operation voltage SV to the voltage converter circuit 140 and the processing unit 130 to serve as an operation power for the voltage converter circuit 140 and the processing unit 130. A capacitor C1 is coupled between an output terminal of the isolation element 122 and the ground terminal GND to achieve a voltage-stabilizing effect. In another embodiment of the present application, the isolation element 122 can also be a direct current (DC) transformer.
The processing unit 130 detects a conducting condition (i.e. a delay angle, wherein the greater the delay angle is, the longer time the triac dimmer 110 is turned off) of the triac dimmer 110 according to a voltage waveform of the first operation voltage FV, so as to deduce a light intensity required by the user. Then, the processing unit 130 adjusts a duty cycle of a pulse width modulation (PWM) signal PWM according to the detected conducting condition. The voltage converter circuit 140 adjusts voltage and current of a driving voltage DV according to the duty cycle of the PWM signal PWM, so as to adjust the brightness of the LED unit 150. The LED unit 150 can be formed by one or a plurality of LEDs connected in series or parallel, which is not limited by the present application. The triac dimmer 110 can also be a different type of dimmer according to a design requirement, for example, a bi-directional thyristor or a field-control thyristor.
A look-up table can be set in the processing unit 130 for recording a corresponding relationship between the duty cycle of the PWM signal PWM and different conducting conditions, and the processing unit 130 can directly adjust the duty cycle of the PWM signal PWM according to the conducting condition of the triac dimmer 110, so as to control the brightness of the LED unit 150. An example of the look-up table is as follows:
The processing unit 130 can directly select a corresponding PWM signal PWM according to the above table one and output it to the voltage converter circuit 140, wherein A, B and C . . . respectively represents the PWM signals PWM having different duty cycles. It should be noticed that the above table one is only an example of the look-up table, and the present application is not limited thereto.
An internal circuit structure of the processing unit 130 is shown in
The determining unit 234 is coupled to the output terminal of the comparator 232, and determines the conducting condition of the triac dimmer 110 according to the PWM signal CS output by the comparator 232. Then, determining unit 234 adjusts the PWM signal PWM output by the pulse width modulator 236 according to the detected conducting condition of the triac dimmer 110 and the look-up table. For example, the greater the delay angle is, the smaller the duty cycle of the PWM signal PWM is.
Then, a corresponding relationship between the first operation voltage FV and the PWM signal CS is described with reference of a waveform diagram. Referring to
The signal waveform 310 within a region 312 is taken as an example to further describe the corresponding relationship of the signal waveforms between the PWM signal CS and the first operation voltage FV. Referring to
Since the processing unit 130 first determines the delay angle of the triac dimmer 110 according to the voltage waveform of the first operation voltage FV, and then correspondingly adjusts the duty cycle of the PWM signal PWM, the PWM signal PWM is rather stable, and is not drifted or becomes unstable due to the waveform variation of the first operation voltage FV. Namely, the duty cycle of the PWM signal PWM is only varied along with the delay angle of the triac dimmer 110. In this way, the brightness of the LED unit 150 can be more stable, so as to avoid a flash phenomenon.
Moreover, it should be noticed that the processing unit 130 can be implemented by an application-specific integrated circuit (ASIC). The signal source 210 can be externally connected or can be configured in the ASIC, which is not limited by the present application. The above voltage converter circuit 140 is, for example, a buck circuit. In another embodiment of the present application, the signal source 210 can also output a DC reference voltage, in this case, the comparator 232 can output a signal with a high voltage level or a low voltage level according to the waveform variation of the first operation voltage FV. When the output of the comparator is changed from the low voltage level to the high voltage level, it represents that the triac dimmer 110 is turned on, so that the delay angle of the triac dimmer 110 can also be detected. Moreover, based on a setting of the DC reference voltage, the first operation voltages FV with too small voltage values can be filtered, so as to avoid the flash phenomenon of the LED unit 150 caused by unstable operation voltages.
In summary, in the present application, the processing unit is used to detect the delay angle of the triac dimmer, so as to output the stable PWM signal to adjust the brightness of the LEDs. Therefore, the brightness of the LEDs can be relatively stable, and the flash phenomenon caused by variation of the voltage output by the triac dimmer can be avoided.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present application without departing from the scope or spirit of the application. In view of the foregoing, it is intended that the present application cover modifications and variations of this application provided they fall within the scope of the following claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 99100022 | Jan 2010 | TW | national |
