Patent Grant
8890431
This application claims the priority of Korean Patent Application No. 10-2011-0051352 filed on May 30, 2011, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to alight emitting diode (LED) driving apparatus capable of preventing a lifespan of an LED from being shortened, and an LED driving method thereof.
2. Description of the Related Art
An LED is a semiconductor device which is formed to have a p-n junction structure and emits light according to electron hole recombination and is applied in various fields in line with recent advancements in semiconductor technology. In particular, since an LED has high efficiency and a long lifespan and is environmentally friendly, compared with existing light emitting devices, it may be applied to many fields
In general, in terms of its structure, an LED can be driven by applying DC power of a few volts thereto, and thus, in general, in order to drive an LED with commercial AC power used in households, offices, or the like, a specific unit of transforming power is required. In order to drive an LED with commercial AC power, an LED driving apparatus typically includes a rectifying circuit, an AC-DC converter, or the like.
However, a general AC-DC converter is voluminous and consumes a great amount of power, so the application of the general AC-DC converter to the LED driving apparatus severely counteracts the advantages of the LED such as high efficiency, small package size, long life span, and the like. Also, a capacitor connected to an output terminal in order to remove a ripple component included in an input signal converted from AC to DC to drive the LED, shortens the lifespan of the LED.
An aspect of the present invention provides an LED driving apparatus capable of stably driving an LED and preventing a lifespan of the LED from being shortened, and an LED driving method thereof.
According to an aspect of the present invention, there is provided an LED driving apparatus including: a rectifying unit rectifying an input signal to generate a first signal; a signal conversion unit inverting the first signal to generate a second signal; and an operation unit arithmetically operating the first and second signals to generate a driving signal.
The LED driving apparatus may further include: a signal level control unit controlling the level of the first signal and transferring the controlled first signal to at least one of the signal conversion unit and the operation unit.
The signal level control unit may include a transformer controlling the level of the first signal.
The LED driving apparatus may further include: a smoothing circuit unit removing a ripple component included in the driving signal.
The smoothing circuit unit may include a multi-layer ceramic capacitor (MLCC).
The signal conversion unit may invert the first signal on the basis of an intermediate value of the first signal corresponding to half of a level peak value of the first signal to generate the second signal.
According to another aspect of the present invention, there is provided a method of driving an LED, including: rectifying an input signal to generate a first signal; inverting the first signal to generate a second signal; and arithmetically operating the first and second signals to generate a driving signal.
The generating of the driving signal may include adding the first and second signals to generate a smoothed DC signal.
The method may further include applying the driving signal to one or more LEDs.
The method may further include removing a ripple component from the driving signal.
In the generating of the second signal, the second signal may be generated by inverting the first signal on the basis of an intermediate value of the first signal corresponding to half of a level peak value of the first signal.
The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the shapes and dimensions may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like components.
Hereinafter, embodiments will be described in detail with reference to the accompanying drawings such that they could be easily practiced by those skilled in the art to which the present invention pertains.
Referring to
The rectifying unit 120 may rectify the input signal supplied from the power 110 through an input terminal to generate the first signal S1, and may output the first signal S1. For example, the rectifying unit 120 may include a diode bridge circuit including four diodes in order to full-wave rectify an AC signal supplied from the power source 110, and a signal level control unit (not shown) for selectively controlling the level of the first signal S1 may be provided with an output terminal of the rectifying unit 120.
When the power source 110 supplies a general AC signal such as commercial power (220V/60 Hz), the rectifying unit 120 converts the AC signal whose direction is changed to the opposite direction at every half period of commercial power into the first signal S1 which flows in one direction, through full-wave rectification. Through this process, the rectifying unit 120 may generate a rectified signal having a doubled frequency as compared with the output signal of the power source 110.
When a signal level control unit is selectively included between the rectifying unit 120 and the signal conversion unit 130, the signal level control unit can adjust the level of the first signal S1 such that the first signal S1 output from the rectifying unit 120 may not have an excessive level of voltage or current. For example, the signal level control unit may be implemented as a transformer or may be implemented as one or more resistors and transistors, or the like.
The signal conversion unit 130 may convert the first signal S1 which has been rectified by the rectifying unit 120 to generate the second signal S2. For example, the signal conversion unit 130 may invert the first signal S1 on the basis of an intermediate value of a first signal S1 level corresponding to half of a peak value of the first signal S1 level to generate the second signal S2.
The signal conversion unit 130 may include an active element such as an operational amplifier (op-amp), a capacitor having a small capacity, and the like. The capacitor included in the signal conversion unit 130 has a relatively very small capacity as compared with that of an electrolytic capacitor used for signal smoothing in a general LED driving apparatus, so it does not greatly affect a shortening of the lifespan of the LED.
The operation unit 140 arithmetically operates the second signal S2 output from the signal conversion unit 130 and the first signal S1 output from the rectifying unit 120 to generate a driving signal SD for operating the light emitting unit 150. When the power source 110 outputs an AC signal such as the commercial power 220V/60 Hz, the rectifying unit 120 may output a rectified signal flowing in one direction, unlike a general AC signal, as a first signal S1, and the signal conversion unit 130 converts a waveform of the first signal S1 to output the second signal S2 having the same phase as that of the first signal S1 and having an upside down (inverted) waveform based on a certain signal level value. For example, the operation unit 140 adds the first signal S1 and the second signal S2 to generate the driving signal SD having a certain value such as that of a DC signal, and applies the driving signal SD to the light emitting unit 150, thereby controlling the operation of the LED without a specific ADC and a capacitor having a large capacity for signal smoothing.
Referring to
As described above with reference to
The first signal S1 output by the rectifying unit 220 is input to an input winding M of the signal level control unit 230, and a plurality of output windings N1 and N2 are disposed at a secondary side of the transformer of the signal level control unit 230. The first output winding N1 may be set to have an appropriate winding ratio (M:N1) with the input winding M, and an electrical signal induced to the first output winding N1 charges electric charges in a capacitor C2 through a diode D1. The electric charges charged in the capacitor C2 may be used to apply voltages VO1 and VO2 required for operating active elements 245 and 255 included in the signal conversion unit 240 and the operation unit 250.
An electrical signal induced to the second output winding N2 by the rectified signal SR applied to the input winding M is input as the first signal S1 to the signal conversion unit 240 and the operation unit 250. The signal conversion unit 240 may include passive elements R and C1 and an active element (i.e., operational amplifier) 245, and as described above, a driving voltage of the active element 245 may be provided from the capacitor C2 connected to the first output winding N1.
Hereinafter, the process of generating the driving signal SD applied to the light emitting unit 260 through the signal level control unit 230, the signal conversion unit 240, and the operation unit 250 will now be described with reference to
The first signal S1 induced to the second output winding N2 appears in the form of a first waveform shown in
As shown in
The second signal S2 output by the active element 245 is expressed by a value obtained by multiplying the difference between the voltage of the capacitor C1 input to the non-inversion terminal and the first signal S1 input to the inversion terminal by the gain of the active element 245. Thus, a signal obtained by subtracting the first signal S1 from the voltage of the capacitor C1 having the same level as the peak value of the first signal S1 is output as the second signal S2 through the output terminal of the active element 245. Through the foregoing process, the second signal S2 in the form of inverting the first signal S1 on the basis of an intermediate value of the first signal S1 level corresponding to half of the peak value of the first signal S1 level is generated.
Namely, the waveform of the second signal S2 output from the signal conversion unit 240 through the active element 245 appears in a form in which the waveform of the first signal S1 is inverted, like a second waveform shown in
The operation unit 250 may include at least one active element 255 as shown in
The sum of the first signal S1 and the second signal S2 is input to the non-inversion terminal of a voltage follower implemented as the active element 255 and transferred to an output terminal of the active element 255. Accordingly, the driving signal SD input to the light emitting unit 260 through the output terminal of the active element 255 appears in the form of a third waveform in
As shown in the third waveform in
Referring to
The signal conversion unit 240 converts the first signal S1 or the rectified signal SR to generate a second signal S2 (S41). When the signal level control unit 230 which can be selectively included in the LED driving apparatus according to an embodiment of the present invention is provided, the signal conversion unit 240 converts the first signal S1 generated by controlling the level of the rectified signal SR to generate the second signal S2. Meanwhile, when the signal level control unit 230 is not provided, since the first signal S1 and the rectified signal SR are the same, the rectified signal SR is directly converted, without performing an additional level control, to generate the second signal S2. As afore-mentioned, the signal conversion unit 240 can generate the second signal S2 which has the same phase as that of the first signal S1 and is in the form in which the waveform of the first signal S1 is inverted upside down. The second signal S2 is input to the operation unit 250.
The operation unit 250 arithmetically operates the first signal S1 and the second signal S2 output from the signal conversion unit 240 (S42). The operation unit 250 may add the second signal S2, which has been obtained by inverting the first signal S1, to the first signal S1, thereby converting an AC type signal having a particular frequency into a DC type driving signal SD for operating the light emitting unit 260. Through such a configuration, the LED driving apparatus can be implemented without an AC-DC converter (ADC).
In case in which the commercial AC signal is intended to be utilized as the input signal Si to drive the LED, if the LED driving apparatus according to an embodiment of the present invention is implemented without the signal level control unit 230, the LEDs included in the light emitting unit 260 would be possibly damaged and the lifespan of the LEDs would be possibly shortened due to an excessive voltage level of the driving signal SD applied to the light emitting unit 260. Thus, the signal level control unit 230 may be disposed between the rectifying unit 220 and the phase controlling unit 240 to adjust the level of the rectified signal SR such that the rectified signal SR has an appropriate level to generate the first signal S1, and the second signal S2 may be generated from the level-controlled first signal S1. Alternatively, the driving signal SD may be generated from the level-unadjusted first signal S1 and the second signal S2, and then, the signal level control unit 230 for controlling the level of the driving signal SD may be disposed at a front stage of the light emitting unit 260, thus solving the foregoing defects.
The operation unit 250 applies the driving signal SD to the light emitting unit 260 including one or more LEDs (S43). The operation unit 250 may apply the driving signal SD to the light emitting unit 260 through a circuit such as a voltage follower. As described above, the driving signal SD is a DC type signal generated by adding a plurality of AC type signals and may include a ripple component to an extent even after entering a stable state. However, since the ripple component included in the driving signal SD is very small, a smoothing electrolytic capacitor disposed between the output terminal of the operation unit 250 and the light emitting unit 260 may be omitted or may be substituted by a capacitor having a very small capacitance. Thus, a degradation of a lifespan of the LED caused as a capacitor having a relatively large capacitance is applied in order to remove a ripple component when the ripple component included in the driving signal SD is large, can be prevented.
As set forth above, according to embodiments of the invention, in using AC power source in an LED driving apparatus for driving one or more LEDs, AC signals, each having a different waveform, are arithmetically operated so as to be generated as an LED driving signal, thus substantially decreasing a ripple component and stably driving the LEDs.
Also, the LED driving apparatus driving one or more LEDs does not use a capacitor or uses a capacitor having a very small capacitance, thus preventing a lifespan of the LEDs from being shortened.
While the present invention has been shown and described in connection with the embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2011-0051352 | May 2011 | KR | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20100213857 | Fan | Aug 2010 | A1 |
| 20110057576 | Otake et al. | Mar 2011 | A1 |
| Number | Date | Country |
|---|---|---|
| 2010-287340 | Dec 2010 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20120306396 A1 | Dec 2012 | US |
