Patent Application
20110279041
1. Technical Field
The present disclosure relates to illumination apparatuses; and particularly to a brightness adjusting method used by an illumination apparatus.
2. Description of Related Art
Light emitting diodes (LEDs) are widely used in various electronic devices, such as a backlight module of a liquid crystal display (LCD). However, in some LCDs, the LEDs often emit light according to a predetermined current supplied by a constant current terminal, such that the brightness of the LEDs maintain a constant brightness regardless of ambient illumination change. This is an inconvenience.
Therefore, there is room for improvement in the art.
Many aspects of the embodiments can be better understood with references to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout two views.
The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one.
Referring to
The power supply 10 is used for providing a voltage to the constant current circuit 20, the detection unit 30 and the PWM circuit 40. The constant current circuit 20 is used for providing a constant current to the illumination unit 50. The detection unit 30 is used for detecting the brightness of the ambient light and generating a detecting signal according to the brightness of the ambient light. In the embodiment, when the brightness of the ambient light increases, the magnitude of the detecting signal increases, if the brightness of the ambient light decreases, the magnitude of the detecting signal decreases.
The PWM circuit 40 is used for generating a pulse voltage according to the detecting signal and the voltage of the power supply, when the magnitude of the detecting signal increases, the duty cycle of the pulse voltage increases. When the magnitude of the detecting signal decreases, the duty cycle of the pulse voltage is decreases.
The illumination unit 50 is used for emitting light according to the duty cycle of the pulse voltage of the PWM circuit 40. In the embodiment, when the duty cycle of the pulse voltage is increased, the luminous intensity of the illumination unit 50 is increased, and when the duty cycle of the pulse voltage is decreased, the luminous intensity of the illumination unit 50 is decreased.
Referring to
The detecting unit 30 includes a photodiode L1, a node 301 and a resistor R1. The photodiode L1 is connected between the first power terminal V1 and the node 301. The first resistor R1 is connected between the node 301 and ground.
The PWM circuit 40 includes a micro control unit (MCU) 410. The MCU 410 includes a first pin 412, a second pin 413 and a third pin 415. The first pin 412 is connected to the first power terminal V1. The second pin 413 is connected to the node 301. The third pin 415 is connected to the illumination unit 50.
The illumination unit 50 includes a transistor Q1 and a plurality of light emitting diodes D1˜Dn. The plurality of the light emitting diodes D1˜Dn are connected with each other in series. The cathode of the first light emitting diode D1 is connected to a drain of the transistor Q1. The anode of the last light emitting diode Dn is connected to the constant current circuit 20. The cathode of the rest of the light emitting diodes is connected to the anode of the adjacent light emitting diode. The anode of the rest of the light emitting diodes is connected to the cathode of the adjacent light emitting diode. A gate of the transistor Q1 is connected to the third pin 415. A source of the transistor Q1 is grounded. The transistor Q1 is an n-channel enhancement type metal oxide semiconductor field effect transistor.
When the brightness of the ambient light is increased, the internal resistance of the photodiode L1 is decreased, such that the voltage of the node 301 increases. The voltage of the second pin 413 will be at the same voltage as the node 301 voltage. The duty cycle of the pulse voltage of the third pin 415 voltage is increased. The period in which the transistor Q1 is turned on is increased, such that the frequency of the D1˜Dn when turned on is increased. The luminous intensity of the illumination apparatus 100 is increased.
When the brightness of the ambient light is decreased, the internal resistance of the photodiode L1 is increased, the voltage of the node 301 decreases. The voltage of the second pin 413 will be at the same voltage as the node 301 voltage. The duty cycle of the pulse voltage of the third pin 415 decreases. The period in which the transistor Q1 is turned off is increased, such that the frequency of the D1˜Dn turned off is increased. The luminous intensity of the illumination apparatus 100 decreases.
A brightness adjusting method is used to adjusting the brightness of the illumination apparatus. The brightness adjusting method includes the following steps.
In step S201, generating a constant current.
In step S202, generating a detecting signal according to the ambient light, if the brightness of the ambient light is increased, the magnitude of the detecting signal increases. If the brightness of the ambient light is decreased, the magnitude of the detecting signal decreases.
In step S203, outputting a pulse voltage according to the detecting signal. When the magnitude of the detecting signal is increased, the duty cycle of the pulse voltage increases. When the magnitude of the detecting signal is decreased, the duty cycle of the pulse voltage decreases.
In step S204, emitting light according to the pulse voltage and the constant current. When the duty cycle of the pulse voltage is increased, the luminous intensity of the illumination apparatus increases. When the duty cycle of the pulse voltage is decreased, the luminous intensity of the illumination apparatus decreases.
Using the above brightness adjusting method, the illumination apparatus can adjust the luminous intensity according to the ambient light, thus the life of the illumination apparatus will increased. In addition, the illumination apparatus can protect the eye of the user.
It is to be understood, even though information and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the present embodiments, the disclosure is illustrative only; and that changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the present embodiments to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201010169093.2 | May 2010 | CN | national |
