Patent Publication Number: US-2011062892-A1

Title: Driving device for a light emitting diode circuit and related lighting device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a driving device for a light emitting diode circuit and related lighting device, and more particularly, to a driving device capable of adjusting light intensity and related lighting device. 
     2. Description of the Prior Art 
     Lighting devices, such as bulbs or fluorescent lamps, are common used in a modern life. A user always switches between different light intensity of a lighting device for a required condition as dinning or reading. Light emitting diodes (LEDs), which provide high intensity and lower power consumption than traditional lighting devices as bulbs, are used in many applications, such as indicator lights or flashlights. 
     Please refer to  FIG. 1 , which is a functional block diagram of an LED lighting device  10  according to the prior art. The lighting device  10  includes an LED circuit  100 , a microcontroller  102  and a pulse width modulation (PWM) control unit  104 , which is used for adjusting multiple level of light intensity and is powered by a power source VCC. The microcontroller  102  generates a control signal V CTRL  corresponding to a specific intensity level, and outputs the control signal V CTRL  to the PWM control unit  104 . The PWM control unit  104  generates a pulse signal V PWM  according to the control signal V CTRL  for controlling the current through the LED circuit  100 , so as to adjust light intensity of the lighting device  10 . 
     Briefly, light intensity of the lighting device  10  is controlled by the microcontroller  102 . However, it is not easy for a user to adjust light intensity of the lighting device  10  as to adjust light intensity of a fluorescent lamp device through a switch. Also, it costs a lot to implement the microcontroller  102 . So far the LED lighting device cannot replace the traditional lighting device. 
     SUMMARY OF THE INVENTION 
     It is therefore a primary objective of the claimed invention to provide a driving device for an LED circuit and related lighting device. 
     The present invention discloses a driving device for an LED circuit. The driving device includes a power receiving terminal, a capacitor, and a light adjusting unit. The power receiving terminal is coupled to a switch for receiving a DC power source that supplies for the LED circuit and the driving device via the switch. The capacitor is coupled to the power receiving terminal, and is utilized for storing energy. The light adjusting unit is coupled to the power receiving terminal and the capacitor, and is utilized for generating a control signal according the status of the switch when a voltage on the capacitor decreases and does not decrease below a first threshold voltage, for adjusting light intensity of the LED circuit. 
     The present invention further discloses a lighting device including an LED circuit, a switch, and a driving device. The switch is coupled to an AC power source that supplies for the light device, and is utilized for controlling an output status of the AC power source. The driving device includes a power receiving terminal, a capacitor, a control unit, and a light adjusting unit. The power receiving terminal is coupled to the switch for receiving a DC power source converted from the AC power source via the switch. The capacitor is coupled to the power receiving terminal, and is utilized for storing energy. The control unit is coupled to the LED circuit, and is utilized for adjusting current consumption of the LED circuit according to a control signal, for driving the LED circuit. The light adjusting unit is coupled to the power receiving terminal, the capacitor, and the control unit, and is utilized for generating the control signal according the status of the switch when a voltage on the capacitor decreases and does not decrease below a first threshold voltage, for adjusting light intensity of the LED circuit. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram of an LED lighting device according to the prior art. 
         FIG. 2  is a functional block diagram of a lighting device according to an embodiment of the present invention. 
         FIG. 3  and  FIG. 4  are waveforms illustrating the voltage detected by the detecting unit in  FIG. 2  and a detecting signal generated by the detecting unit. 
         FIG. 5  is a functional block diagram of a lighting device according to an embodiment of the present invention. 
         FIG. 6  and  FIG. 7  are waveforms illustrating the voltage detected by the detecting unit in  FIG. 5  and a detecting signal generated by the detecting unit. 
         FIG. 8  is a functional block diagram of a lighting device according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 2 , which is a functional block diagram of a lighting device  20  according to an embodiment of the present invention. The lighting device  20  is an LED lighting device, and the required power is provided by an alternating current (AC) power source VCC. The lighting device  20  comprises an LED circuit  200 , a switch  202 , a power converter  203 , and a driving device  204 . The LED circuit  200  includes multiple LEDs in series or in parallel. The switch  202  is coupled between the AC power source VCC and the power converter  203 , and is utilized for controlling whether the AC power source VCC is outputted to the power converter  203 . The power converter  203  is utilized for converting the AC power source VCC into a direct current (DC) power source that is used for the LED circuit  200  and the driving device  204 . The driving device  204  is coupled to the LED circuit  200  and the power converter  203 , and is utilized for driving the LED circuit  200  and adjusting light intensity of the LED circuit  200 , which is described in detail as follows. 
     The driving device  204  comprises a power receiving terminal VIN coupled to the power converter  203 , a capacitor  210 , a light adjusting unit  212 , and a control unit  216 . When the switch  202  is turned on, the power receiving terminal VIN receives DC power source generated by the power converter  203 . The capacitor  210  is coupled to the power receiving terminal VIN, and is utilized for storing energy. The light adjusting unit  212  is coupled to the power receiving terminal VIN, the capacitor  210 , and the control unit  216 , and is utilized for generating a control signal SC that is outputted to the control unit  216  according to on/off states of the switch  202  when a voltage on the capacitor  210  decreases and does not decrease below a threshold voltage VTH 1 , which is a minimal operation voltage of the adjusting unit  212 . The control unit  216  is coupled to the light adjusting unit  212  and the LED circuit  200 , and is utilized for adjusting an operating current of the LED circuit  200  according to the control signal SC, or adjusting a number of lightened LEDs, so as to drive the LED circuit  200  to generate the light of different light intensity, e.g. full light, dim light, etc. The control unit  216  can be implemented in different circuitry and is not restricted in the embodiment of the present invention. 
     Note that, the driving device  204  implements multilevel light intensity adjustment. The light adjusting unit  212  comprises a detecting unit  220  and a counter  222 . The detecting unit  220  is coupled to the power receiving terminal VIN and the capacitor  210 , and is utilized for generating a detecting signal SD according to on/off state of the switch  202  when the voltage of the capacitor  210  decreases and does not decrease below the threshold voltage VTH 1 . When the switch  202  is turned off, the voltage on the power receiving terminal VIN start decreasing. When the detecting unit  220  detects that the voltage on the power receiving terminal VIN decreases below a threshold voltage VTH 2 , the voltage level of the detecting signal SD converts, such as from a high voltage level to a low voltage level. 
     The counter  222  is coupled to the detecting unit  220 , the capacitor  210 , and the control unit  216 , and is utilized for counting the number of times of the detecting signal SD converting from the high voltage level to the low voltage level when the switch  202  is turned off and the voltage on the capacitor  210  does not decrease below the threshold voltage VTH 1 , for generating the corresponding control signal SC. During the counter  222  counts the number of times of the detecting signal SD converting from the high voltage level to the low voltage level, the power source that the counter  222  requires comes from the energy stored in the capacitor  210 . For example, when the switch  202  is turned on and off by three times before the voltage on the capacitor  210  decreases below the threshold voltage VTH 1 , the detecting signal SD is affected and converts from the high voltage level to the low voltage level for three times, which is counted by the counter  222 . The counter  222  generates the control signal SC corresponding to three times of voltage level converting from high to low, which controls the LED circuit  200  to generate a dim light. 
     The detecting unit  220  is a voltage detector whose reference voltage as the threshold voltage VTH 2 , for example. When the detecting unit  220  detects a voltage higher than the threshold voltage VTH 2 , the detecting signal SD outputted by the detecting unit  220  is at a high voltage level, and when the detecting unit  220  detects a voltage lower than the threshold voltage VTH 2 , the detecting signal SD is at a low voltage level. In the driving device  204 , the operation voltage of the detecting unit  220  and the operation voltage of the counter  222  are set different for preventing the condition that the detecting unit  220  outputs the detecting signal SD by a wrong voltage level when the switch  202  is turned off due to the voltage on the capacitor  210 . 
     When the switch  202  is turned off, the power converter  203  does not output DC power source to the light adjusting unit  212 ; meanwhile, the power sources which the detecting unit  220  and the counter  222  require are supplied by energy stored in the capacitor  210 . During the time when the voltage on the capacitor  210  decreases but does not decrease below the threshold voltage VTH 1 , each time the switch  202  is turned off, the detecting signal SD is turned from a high voltage level to a low voltage level. The counter  222  counts how many times the detecting signal SD is turned from the high voltage level to the low voltage level, and outputs the control signal SC corresponding to the counted times. Therefore, when the switch  202  is turned on, the control unit  216  controls the operation current of the LED circuit  200  according to the control signal SC, so that the LED circuit  200  are lightened with the desired light intensity. 
     Please refer to  FIG. 3  and  FIG. 4 , which illustrate relationship between the voltage detected by the detecting unit  220  in  FIG. 2  and the detecting signal SD. Note that in  FIG. 2 , the detecting unit  220  detects the voltage on the capacitor  210 . The threshold voltage VTH 1  is the minimal operation voltage of the light adjusting unit  212  and is also the reset voltage of the counter  222 ; the threshold voltage VTH 2  is the reference voltage of the detecting unit  220 . As shown in  FIG. 3 , when the voltage detected by the detecting unit  220  decreases below the threshold voltage VTH 2  (but does not decrease below the threshold voltage VTH 1  yet), the detecting signal SD is turned from the high voltage level to the low voltage level. When the voltage detected by the detecting unit  220  rises over the threshold voltage VTH 2 , the detecting signal SD is turned from the low voltage level to the high voltage level again. As shown in  FIG. 4 , when the voltage detected by the detecting unit  220  decreases below the threshold VTH 1 , the counter  222  is reset, which means that the control signal SC is reset to an initial value that leads to a default light intensity. 
     As mentioned previously, a conventional lighting device uses an expensive microcontroller to adjust light intensity of an LED circuit. In comparison, in the lighting device  20 , the present invention uses low-cost and simple components, such as a voltage detector and a counter, to implement the similar light intensity adjustment. Therefore, cost of the lighting device  20  is reduced. The present invention also uses a capacitor for storing energy and supplying power source for the counter  222  when the switch  202  is turned off, so that the light intensity adjustment can be operated successfully. The driving device  204 , except the capacitor  210 , is usually implemented into an LED driver IC, and the capacitor  210  is off chip. 
     The present invention further provides an embodiment for solving issues that the energy stored in the capacitor  210  has a limit, and the output voltage of the power converter  203  may be higher than a maximal operation voltage of the light adjusting unit  212 . Please refer to  FIG. 5 , which is a functional block diagram of a lighting device  50  according to an embodiment of the present invention. Similar to the lighting device  20  in  FIG. 2 , the lighting device  50  comprises the LED circuit  200 , the switch  202 , the power converter  203 , the driving device  204 , and further comprises a regulator  500 , and a regulator  502 . The regulator  500  is coupled between the power receiving terminal VIN and the counter  222 , and is used as a single directional component. By the use of the regulator  500 , the energy stored in the capacitor  210  are only used for the counter  222  when the switch  202  is turned off, and thereby the counter  222  cannot be reset soon. In another embodiment of the present invention, the regulator  500  is replaced by another single directional component, such as a diode, or a transistor. The regulator  502  is coupled between the power converter  203  and the power receiving terminal VIN, and is utilized for converting the voltage outputted by the power converter  203  into a voltage that is appropriate to be the operation voltage of the light adjusting unit  212 . Please refer to  FIG. 6  and  FIG. 7 , which illustrate relationship between the voltage detected by the detecting unit  220  in  FIG. 5  and the detecting signal SD. Note that, the voltage detected by the detecting unit  220  in  FIG. 5  is different from the voltage on the capacitor  210 . 
     In the lighting device  20 , the operation voltage of the counter  222  is assumed to be the same as the operation voltage of the control unit  216 , and the power sources of the counter  222  and the control unit  216  are both provided via the detecting unit  220 . In this situation, the use of the energy stored in the capacitor  210  is not optimized. Please refer to  FIG. 8 , which is a functional block diagram of a lighting device  80  according to an embodiment of the present invention. The lighting device  80  comprises not only all of units in the lighting device  20  but also comprises a regulator  800  and a voltage detector  802 . The regulator  800  is coupled between the power converter and the power receiving terminal VIN, and is utilized for converting the voltage outputted by the power converter  203  into another voltage appropriate to be the operation voltage of the light adjusting unit  212 . The voltage detector  802  is coupled between the power receiving terminal VIN and the control unit  216 , and the operation voltage of the voltage detector  802  is higher than the detecting unit  220  and the counter  222 . When the voltage on the power receiving terminal VIN is higher than a reference voltage of the voltage detector  802 , the voltage detector  802  outputs a DC power source to the control unit  216 , wherein the voltage of the DC power source is equal to the voltage on the power receiving terminal VIN. Therefore, when the switch  202  is turned off and the voltage on the power receiving terminal VIN decreases, the voltage detector  802  is turned off earlier, and the energy stored in the capacitor  210  only provides for the counter  222 . As in  FIG. 8 , energy stored in the capacitor  210  is used efficiently without a single directional component. 
     The lighting device  20 ,  50 , and  80  are embodiments of the present invention, and those skilled in the art can make alterations and modifications accordingly. The single directional component, the regulator, or the voltage detector can be added or removed depends on requirement. In the lighting devices  20 ,  50 , and  80 , the counter  222  receives the detecting signal SD and a power source via the detecting unit  220 ; the detecting unit  220  receives a power source generated by the power converter  203 , and detects whether the switch  202  is turned off according to the power source. In another embodiment, the counter  222  can receive a signal generated according to an AC power source behind the switch  202  as a detecting signal instead of the detecting signal SD outputted by the detecting unit  220 . Besides, the detecting unit  220  can be coupled to anyplace between the switch  202  and the power receiving terminal VIN, to detect whether the switch is turned off through the AC power source or the DC power source. 
     In conclusion, the present invention uses simple circuitry including the detecting unit and the counter to implement light adjusting function. The present invention uses a capacitor to store energy and maintains operation of the counter when the switch is turned off. Besides, the present invention uses a single directional component, a regulator, or a voltage detector to avoid that the energy stored in the capacitor is wasted soon. Therefore, the counter is not reset frequently, and convenience for adjusting light intensity is improved. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.