Patent Application
20090153076
The present invention relates to a diving circuit and a driving method, and more particularly to a diving circuit and a driving method for reducing the operating temperature of a LED package.
In recent years, light emitting diodes (LEDs) capable of emitting light with high luminance and high illuminating efficiency have been developed. In comparison with a common incandescent light, a LED has lower power consumption, long service life, and quick response speed. With the maturity of the LED technology, LEDs will replace all conventional lighting facilities. Until now, LEDs are widely used in many aspects of daily lives, such as automobile lighting devices, handheld lighting devices, backlight sources for LCDs, traffic lights, indicator board displays, and the like.
For most LED packages, there are two mechanisms for dissipating heat, i.e. an internal heat-dissipation mechanism and an external heat-dissipation mechanism. The internal heat-dissipation mechanism uses a thermal conductive body inside the LED package to remove the heat generated from the LED chip to the ambient surroundings. The external heat-dissipation mechanism uses a heat sink or a fan outside the LED package to facilitate heat radiation.
Referring to
The LED package 10 further includes a second substrate 104. An anode conductive part 104a and a cathode conductive part 104b are formed on the second substrate 104. Via the substrate conductor 106, the first electrical conductive part 102a and the second electrical conductive part 102b are electrically connected with the anode conductive part 104a and the cathode conductive part 104b of the second substrate 104, respectively.
In practical application, the LED package 10 is formed on a printed circuit board 11. An electrical conductive layer 111 is formed on the printed circuit board 11. The anode conductive part 104a and the cathode conductive part 104b of the second substrate 104 are contacted with the electrical conductive layer 111 of the printed circuit board 11, so that the electricity may be transmitted from the printed circuit board 11 to the LED chip 101 of the LED package 10 to illuminate light. The heat generated from the LED package 10 during operation will be transmitted to the outside of the LED package 10 through the thermal conductive body 103. For facilitating heat radiation, a first heat sink 12 and a second heat sink 13 are arranged outside the LED package 10. Generally, the first heat sink 12 and the second heat sink 13 may be directly or indirectly contacted with or connected to the thermal conductive body 103 of the LED package 10. As a consequence, the first heat sink 12 and a second heat sink 13 may facilitate dissipating heat to the ambient surroundings in a passive manner. In addition to the heat sink, an air flow generating device such as a fan may be used to facilitate dissipating heat to the ambient surroundings in an active manner.
Since a great amount of heat is generated from the LED chip 101, the internal heat-dissipation mechanism of using the thermal conductive body 103 and/or the external heat-dissipation mechanism of using the heat sinks 12 and 13 are usually insufficient to dissipate away the heat. If the heat generated from the LED chip is not effectively dissipated away, the higher operating temperature may degrade the performance of the LED package or eventually leads to device failure. Moreover, the external heat-dissipation mechanism is not cost-effective. If the air flow generating device has a breakdown, the operating temperature of the LED chip is abruptly increased.
There is a need of providing a diving circuit and a driving method for reducing the operating temperature of a LED package to obviate the drawbacks encountered from the prior art.
It is an object of the present invention to provide a diving circuit and a driving method for reducing the operating temperature of a LED package in order to avoid the problems encountered from the conventional heat-dissipation mechanisms.
In accordance with an aspect of the present invention, there is provided a driving circuit for driving one or multiple LED chip sets. The driving circuit includes a power converting circuit, one or multiple switching elements, and a controller. The power converting circuit is electrically connected to the one or multiple LED chip sets for receiving an input power and converting the input power into a regulated output voltage or current required for illuminating the one or multiple LED chip sets. The one or multiple switching elements electrically connected to the one or multiple LED chip sets. The controller is electrically connected to the switching elements for controlling alternate or combined simultaneous/alternate switching on/off statuses of the one or multiple switching elements, so that the one or multiple LED chip sets emit light in an alternate lighting manner or a combined simultaneous/alternate lighting manner to reduce the operating temperatures of the one or multiple LED chip sets.
In accordance with another aspect of the present invention, there is provided a driving circuit for driving one or multiple LED chip sets. The driving circuit includes a power converting circuit and a waveform generator. The power converting circuit is used for receiving an input power and converting the input power into a regulated output voltage or current required for illuminating the one or multiple LED chip sets. The waveform generator is electrically connected to the power converting circuit and the one or multiple LED chip sets for generating a control wave with positive and negative voltages, wherein the one or multiple LED chip sets in an alternate lighting manner in response to the positive and negative voltages of the control wave.
In accordance with another aspect of the present invention, there is provided a method of reducing the operating temperature of a LED package including one or multiple LED chip sets. First of all, a driving circuit is provided and electrically connected with the one or multiple LED chip sets. By the driving circuit, the one or multiple LED chip sets are driven and controlled to emit light in the alternate lighting manner or a combined simultaneous/alternate lighting manner so as to reduce the operating temperatures of the one or multiple LED chip sets.
The above contents of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which:
The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.
In some embodiments, the driving circuit 2 further includes a first impedance element 27 (e.g. a first resistor) and a second impedance element 28 (e.g. a second resistor). The first impedance element 27 is connected in series with the first LED chip set 25. The second impedance element 28 is connected in series with the second LED chip set 26. By means of the first impedance element 27 and the second impedance element 28, the problem of causing instable brightness of emitted light due to temperature variations is alleviated.
In some embodiments, the power converting circuit 21 includes a filter 211, a power factor correction unit 212, a DC-to-DC converting unit 213 and a pulse width modulation (PWM) controller 214. The filtering unit 211 is interconnected between the input terminal 21b of the power converting circuit 21 and the power factor correction unit 212 for filtering the input power Vin. The power factor correction unit 212 is interconnected between the filtering unit 211 and the DC-to-DC converting unit 213 for correcting the power factor of the power converting circuit 21 and converting the alternating voltage of the input power Vin into a DC voltage, which is transmitted to the DC-to-DC converting unit 213. The DC-to-DC converting unit 213 is interconnected between the power factor correction unit 212 and the output terminal 21a of the power converting circuit 21 for converting the DC voltage into a regulated output voltage or current required for illuminating the first LED chip set 25 and the second LED chip set 26. The PWM controller 214 is interconnected between the power factor correction unit 212 and the DC-to-DC converting unit 213 for controlling operations of the power factor correction unit 212.
A further embodiment of a driving circuit 3 is illustrated in
In some embodiments, the first LED chip set 25 and the second LED chip set 26 included in the driving circuit 2 or 3 may be packaged as a single LED package or formed as individual LED packages according to the conventional packaging technology. Each of the first LED chip set 25 and the second LED chip set 26 includes at least one LED chip. For clarification, each of the first LED chip set 25 and the second LED chip set 26 with one LED chip is illustrated as follows.
At t=t0, the driving circuit 2 is activated, and the controller 22 issues an enabling signal (e.g. a high-level voltage) to the first switching element 23. In response to the enabling signal, the first switching element 23 is turned on and thus the power converting circuit 21 transmits electricity to the first LED chip set 25 to illuminate the first LED chip set 25. As the operating time elapses, the LED brightness gradually reaches to its maximum value and is then slightly reduced to a specified value. In the stage from t=t0 to t=t1, the operating temperature of the LED chip is substantially in direct proportion to the operating time. In other words, the operating temperature of the first LED chip set 25 is increased as the operating time is increased.
At t=t1, the controller 22 issues an enabling signal to the second switching element 24 while issuing a disenabling signal (e.g. a low-level voltage) to the first switching element 23. In response to the enabling signal, the second switching element 24 is turned on and thus the power converting circuit 21 transmits electricity to the second LED chip set 26 to illuminate the second LED chip set 26. Whereas, in response to the disenabling signal, the first switching element 23 is turned off to interrupt the illumination of the first LED chip set 25. In the stage from t=t1 to t=t2, the brightness of the first LED chip set 25 is gradually decreased but the brightness of the second LED chip set 26 is gradually increased to be close to its maximum value. As a consequence, the brightness of the light emitted from the overall LED package maintains at a desired level of nearly the maximum value. Moreover, in the stage from t=t1 to t=t2, the operating temperature of the second LED chip set 26 is gradually increased but the operating temperature of the first LED chip set 25 is gradually decreased. As a consequence, the operating temperature of the overall LED package maintains at an acceptable level.
Similarly, in the stage from t=t2 to t=t3, the first LED chip set 25 is controlled by the controller 22 to emit light but the illumination of the second LED chip set 26 is interrupted. In the stage from t=t3 to t=t4, the first LED chip set 25 is controlled by the controller 22 to interrupt illumination but the second LED chip set 26 is controlled to emit light. In the stage from t=t4 to t=t5, the first LED chip set 25 is controlled by the controller 22 to emit light but the illumination of the second LED chip set 26 is interrupted. The rest may be deduced by analog. Accordingly, by alternately lighting the first LED chip set 25 and the second LED chip set 26, the brightness of the light emitted from the overall LED package maintains at a desired level, which is substantially equal to the brightness of the light emitted from a single LED chip set. More especially, the operating temperature of the overall LED package may be reduced to approximately a half of the operating temperature of a single LED chip set. In some embodiments, at least two LED chip sets are packaged as the LED package, and the size of the overall LED package is considerably reduced when compared with the conventional LED package. Since the operating temperature of the overall LED package is largely reduced by the driving circuit of the present invention, the cost associated with heat dissipation is reduced.
In the above embodiments, the first switching element 23 and the second switching element 24 are controlled by the controller 22 to be alternatively turned on or turned off, so that the first LED chip set 25 and the second LED chip set 26 can emit light in an alternate lighting manner. It is noted that, however, those skilled in the art will readily observe that numerous modifications and alterations of the lighting manner may be made while retaining the teachings of the invention. For example, the on/off statuses of the first switching element 23 and the second switching element 24 may be partially overlapped with each other, as can be seen in
In the above embodiments, the driving circuit is implemented in a digital form. Nevertheless, the driving circuit of the present invention may be implemented in an analog form.
In this embodiment, the directions of the current passing through the first LED chip set 25 and the second LED chip set 26 are opposed to each other. During a certain interval, only one of the first LED chip set 25 and the second LED chip set 26 is turned on to emit light. For example, the first LED chip set 25 is turned on to emit light in response to the positive voltage of the control wave outputted from the waveform generator 71, but the second LED chip set 26 is turned on to emit light in response to the negative voltage of the control wave outputted from the waveform generator 71. As the control wave with positive and negative voltages is continuously generated from the waveform generator 71, the first LED chip set 25 and the second LED chip set 26 emit light in an alternate lighting manner. In some embodiments, a transient zero voltage is intervened between the positive and negative voltages. During the time interval corresponding to the zero voltage, the first LED chip set 25 and the second LED chip set 26 both interrupt illumination. In some embodiments, the durations of the positive voltage and the negative voltage may be identical or varied according to the performance requirement of respective LED chip sets.
In some embodiments, the driving circuit 7 further includes a first impedance element 27 (e.g. a first resistor) and a second impedance element 28 (e.g. a second resistor). The first impedance element 27 is connected in series with the first LED chip set 25. The second impedance element 28 is connected in series with the second LED chip set 26. By means of the first impedance element 27 and the second impedance element 28, the problem of causing instable brightness of emitted light due to temperature variations is alleviated.
Please refer to
Furthermore, the waveform generator 71 includes a third switching element Q3, a fourth switching element Q4, a transformer Ta, a third resistor R3, a fourth resistor R4, an output inductor Lo, an output capacitor Co and a second capacitor Cb. The emitter of the third switching element Q3 is coupled to the fourth resistor R4, the first winding coil S1 and the third winding coil S3 of the transformer Ta. The base of the third switching element Q3 is coupled to the third resistor R3 and the first winding coil S1 of the transformer Ta. The collector of the third switching element Q3 is coupled to the positive end of the power converting circuit 21. The emitter of the fourth switching element Q4 is coupled to the negative end of the power converting circuit 21. The base of the fourth switching element Q4 is coupled to the second winding coil S2 of the transformer Ta. The collector of the fourth switching element Q4 is coupled to the fourth resistor R4. The output capacitor Co is coupled to the output terminal of the waveform generator 71 and connected in series with the output inductor Lo, the second capacitor Cb and the third winding coil S3 of the transformer Ta.
In this embodiment, when the third switching element Q3 is turned on but the fourth switching element Q4 is turned off, a close loop is defined by the third switching element Q3, the third winding coil S3 of the transformer Ta, the output inductor Lo, the output capacitor Co and the second capacitor Cb, so that a positive voltage is outputted from the waveform generator 71 to illuminate the first LED chip set 25. Whereas, when the third switching element Q3 is turned off but the fourth switching element Q4 is turned on, a close loop is defined by the fourth switching element Q4, the third winding coil S3 of the transformer Ta, the output inductor Lo, the output capacitor Co and the second capacitor Cb, so that a negative voltage is outputted from the waveform generator 71 to illuminate the second LED chip set 26. Accordingly, the first LED chip set 25 and the second LED chip set 26 emit light in an alternate lighting manner, thereby decreasing the operating temperature of the overall LED package.
From the above description, by using the driving circuit and the driving method of the present invention, one or multiple LED chip sets emit light in an alternate lighting manner or in a combined simultaneous/alternate lighting manner in order to reduce the operating time. According to an alternate lighting manner or the combined simultaneous/alternate lighting manner, the operating time of individual LED chips is reduced and the junction temperature of individual LED chips is lowered. As a consequence, the illuminating efficiency of the overall LED package is increased and the brightness of the light emitted from the overall LED package maintains at a desired level. Since the problems encountered from the conventional heat-dissipation mechanisms are overcome, the LED package of the present invention is advantageous in the aspects of heat-dissipating efficiency and cost-effectiveness.
While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 096147817 | Dec 2007 | TW | national |
