US20070114949A1 - Pwm illumination control circuit with low visual noise for driving led - Google Patents
Pwm illumination control circuit with low visual noise for driving led Download PDFInfo
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- US20070114949A1 US20070114949A1 US11/623,326 US62332607A US2007114949A1 US 20070114949 A1 US20070114949 A1 US 20070114949A1 US 62332607 A US62332607 A US 62332607A US 2007114949 A1 US2007114949 A1 US 2007114949A1
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- illumination control
- control pulse
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/10—Controlling the intensity of the light
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
- H05B45/37—Converter circuits
- H05B45/3725—Switched mode power supply [SMPS]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
- Y02B20/30—Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
Definitions
- the present invention relates to an illumination control circuit. More particularly, the present invention relates to a pulse width modulation (PWM) illumination control circuit with low visual noise for driving a light-emitting diode (LED).
- PWM pulse width modulation
- LCD liquid crystal displays
- a liquid crystal display uses an array of light-emitting diodes (LED) driven by a simple driving circuit to serve as the light source.
- LED light-emitting diodes
- brightness of the LED is not linearly related to the driving current.
- color of the LED may also vary according to the driving current.
- difficulties are often encountered when the illumination is varied by directly adjusting the driving current.
- a constant amplitude driving current is used with illumination adjustment achieved through a pulse width modulation (PWM) of the driving current.
- PWM pulse width modulation
- FIG. 1 is a block diagram of a conventional pulse width modulation illumination control circuit.
- FIG. 2 is a diagram showing the relationships between illumination control pulse signals and light-emitting diode driving current signals for the circuit in FIG. 1 .
- an illumination control pulse signal Con that set the illumination of the light-emitting diode is sent to a DC/DC converter 110 to produce a light-emitting diode driving current signal Id for driving a light-emitting diode.
- the waveform diagrams (a), (b) and (c) in FIG. 2 represent three different pulse width settings of the light-emitting diode driving current signals Id.
- the light-emitting diode is at full illumination (100%) in FIG. 2 ( a ), at 20% of the full illumination in FIG. 2 ( b ) and at 50% of the full illumination in FIG. 2 ( c ).
- the frequency of the illumination control pulse signal Con cannot be too low, typically above 200 Hz.
- the illumination control pulse signal Con must operate at a sufficiently high frequency so that the human eyes can retain a visual image and yet perceive a steady change of illumination without flickering.
- these control signals may be implemented using a simple switching circuit that controls the on/off states of the entire DC/DC converter.
- the frequency and duty cycle of the aforementioned illumination control pulse signal Con is set to be fixed according to the required illumination, interference with the vertical, horizontal scanning signals may occur when used as back light in a liquid crystal display.
- the difference in frequency between the back light and the video signals often leads to the so-called ‘fanning effect’, a watery wave pattern of the image on a display screen.
- the switching on or off of the DC/DC converter also leads to a significant loading on the power supply that provides power to the DC/DC converter.
- a ripple waveform synchronized with the illumination control pulse signal Con is also produced in the power supply. Once again, the ripple waveform may affect the video display signals leading to a flickering screen.
- the illumination control pulse signal Con and the horizontal scanning signals are synchronized to a frequency an integral multiple of each other.
- this arrangement will increase the production cost.
- the frequency of the illumination control pulse signal Con can be increased.
- increasing the frequency of pulse signal Con leads to higher power consumption.
- fabricating a light-emitting diode illuminated liquid crystal display with low noise and broad adjustable range of illumination is increasingly difficult.
- one objective of the present invention is to provide a pulse width modulation (PWM) illumination control circuit with low visual noise for driving a light-emitting diode (LED).
- PWM pulse width modulation
- LED light-emitting diode
- the invention provides a low visual noise pulse width modulation illumination control circuit for controlling the illumination of light-emitting diodes inside a liquid crystal display.
- the low visual noise pulse width modulation illumination control circuit comprises an illumination control pulse generating unit and a DC/DC converter.
- the illumination control pulse-generating unit receives an illumination-adjusting signal. According to the illumination-adjusting signal, the illumination control pulse-generating unit generates an illumination control pulse signal having a duty cycle set to vary within a predetermined range.
- the DC/DC converter is coupled to the illumination control pulse-generating unit so that the illumination control pulse-generating unit can drive the light-emitting diodes according to the illumination control pulse signal.
- the illumination control pulse-generating unit of the low visual noise PWM illumination control circuit further comprises a noise generator, an analogue adder and a comparator.
- the noise generator generates a noise signal.
- the analogue adder is coupled to the noise generator for receiving the illumination-adjusting signal and the noise signal to produce a noise signal loaded illumination-adjusting signal.
- the comparator is coupled to the analogue adder for comparing the noise signal loaded illumination-adjusting signal with a triangular wave and producing the illumination control pulse signal.
- the noise signal level produced by the low visual noise PWM illumination control circuit can be adjusted.
- the present invention also provides an alternative low visual noise pulse width modulation illumination control circuit for controlling the illumination of light-emitting diodes inside a liquid crystal display.
- the low visual noise pulse width modulation illumination control circuit comprises an illumination control pulse generating unit and a DC/DC converter.
- the illumination control pulse-generating unit receives an illumination-adjusting signal. According to the illumination-adjusting signal, the illumination control pulse-generating unit generates an illumination control pulse signal having a frequency set to vary within a predetermined range.
- the DC/DC converter is coupled to the illumination control pulse-generating unit so that the illumination control pulse-generating unit can drive the light-emitting diodes according to the illumination control pulse signal.
- the operations carried out by the illumination control pulse-generating unit of the low visual noise PWM illumination control circuit are implemented using a microprocessor.
- the phase of the illumination control pulse signal produced by the low visual noise PWM illumination control circuit also varies within a predetermined range.
- the present invention provides a low visual noise PWM illumination control circuit for driving light-emitting diodes such that visual noise interference due to pulse width modulation is reduced by varying the duty cycle or frequency of an illumination control pulse signal and maintaining an average duty cycle and frequency.
- FIG. 1 is a block diagram of a conventional pulse width modulation illumination control circuit.
- FIG. 2 is a diagram showing the relationships between illumination control pulse signals and light-emitting diode driving current signals for the circuit in FIG. 1 .
- FIG. 3 is a block diagram of a light-emitting diode low visual noise PWM illumination control circuit according to one preferred embodiment of the present invention.
- FIG. 4 is a circuit diagram of an illumination control pulse-generating unit according to the preferred embodiment of the present invention.
- FIG. 5 is a diagram showing the waveform of the illumination control pulse signal produced by the illumination control pulse-generating unit shown in FIG. 4 .
- FIG. 6 is a flow chart showing the steps for operating the illumination control pulse-generating unit according to the preferred embodiment of the present invention.
- FIG. 3 is a block diagram of a light-emitting diode low visual noise PWM illumination control circuit according to one preferred embodiment of the present invention.
- the low visual noise pulse width modulation (PWM) illumination control circuit 300 in FIG. 3 is adapted to control the illumination level of light-emitting diodes (not shown) inside a liquid crystal display.
- the low visual noise PWM illumination control circuit 300 comprises an illumination control pulse-generating unit 310 and a DC/DC converter 320 .
- the illumination control pulse-generating unit 310 is used for receiving an illumination-adjusting signal Ref. According to the illumination-adjusting signal Ref, the illumination control pulse-generating unit 310 generates an illumination control pulse signal Con.
- the duty cycle or frequency of the illumination control pulse signal Con is permitted to vary within a predetermined range. Hence, differential frequency interference between a fixed illumination control pulse signal Con and the vertical/horizontal scanning signal leading to the so-called ‘fanning effect’ with wavy lines on the display screen is prevented.
- the DC/DC converter 320 drives the light-emitting diodes according to the illumination control pulse signal Con generated by the illumination control pulse-generating unit 310 .
- FIG. 4 is a circuit diagram of an illumination control pulse-generating unit according to the preferred embodiment of the present invention.
- the illumination control pulse-generating unit 400 comprises a noise generator 410 , an analogue adder 420 and a comparator 430 .
- the noise generator 410 further comprises a resistor 411 and an amplifier 421 electrically connected together and the analogue adder 420 further comprises a plurality of resistors 422 , 423 , 425 and an amplifier 421 electrically connected together.
- the noise generator 410 outputs a noise signal Nos after the amplifier 412 inside the noise generator 410 amplifies the thermal noise produced by the resistor 411 .
- the noise signal Nos is transmitted to the analogue adder circuit 420 such that the noise signal Nos and an illumination-adjusting signal Ref originally set to control the output duty cycle of the DC voltage are summed together to produce a noise signal loaded illumination-adjusting signal Ref.
- the resistor 422 is a variable resistor so that the level of the noise signal Nos loaded on the illumination-adjusting signal Ref can be adjusted.
- the noise signal loaded illumination-adjusting signal Ref is transmitted to the comparator 430 where the signal is compared with a triangular wave Tri to produce an illumination control pulse signal Con having a duty cycle that varies within the acceptable noise signal level as shown in FIG. 5 .
- the duty cycle of the illumination control pulse signal Con varies on each transient moment of each cycle, the average power of the noise is zero.
- the average duty cycle of the entire circuit after adding the noise is identical to one without adding any noise.
- the illumination of the light-emitting diodes after adding noise to the circuit is identical to the illumination without adding any noise to the circuit.
- FIG. 6 is a flow chart showing the steps for operating the illumination control pulse-generating unit according to the present invention.
- the illumination control pulse-generating unit 310 as shown in FIG. 3 is implemented using a microprocessor, the steps in FIG. 6 can be carried out to produce an illumination control pulse signal Con with a variable frequency so that visual noise interference due to pulse width modulation is reduced.
- the n illumination control pulse signals Con with different cycle time can be permuted to form a queue before turning each signal out sequentially. For example, if sequence 0 is ⁇ T0, T1, T2, . . . , Tn ⁇ 1 ⁇ , sequence 1 is ⁇ T0, T2, . . .
- the n illumination control pulse signals Con with different cycle time may be arranged to form a list of K different non-repeating sequence including sequence 0, sequence 1, sequence 2, . . . , sequence K ⁇ 1. Thereafter, the steps depicted in FIG. 6 can be executed using the microprocessor so that illumination control pulse signals Con each having a different frequency are sequentially output.
- the operating steps of a digitally operated illumination control pulse-generating unit with a low visual noise level are explained as follows.
- step S 610 variables I, J are set to 0. Thereafter, in step S 620 , the I th illumination control pulse signal cycle in sequence J and the received illumination-adjusting signal are combined to produce an illumination control pulse signal.
- step S 630 a 1 is added to the variable I in preparation for retrieving the next illumination control pulse signal cycle in sequence J.
- step S 640 the value of I is checked to determine whether it is equal to n. When the value of I is not equal to n, the operation returns to step S 620 . However, if the value of I is equal to n, step S 650 is executed to reset I to 0 and add 1 to the value of J in preparation for retrieving the first illumination control pulse signal cycle of the next sequence.
- step S 660 is executed to determine whether the value of J is equal to K. When the value of J is not equal to K, the operation returns to step S 620 . On the other hand, if the value of J is equal to K, step S 670 is executed to reset the value of J to 0 and return the operation to step S 620 .
- step S 620 can be set to vary within a predetermined range so that an illumination control pulse signal with a wider frequency range is produced.
Abstract
A pulse width modulation (PWM) illumination control circuit with low visual noise for driving a light-emitting diode (LED) is provided. An illumination control pulse-generating unit is used to generate an illumination control pulse signal according to an illumination-adjusting signal. The duty cycle or frequency of the illumination control pulse signal varies within a predetermined scope for controlling a DC/DC converter to drive the light-emitting diode so that overall visual noise level of the PWM illumination control circuit is improved.
Description
- This application is a divisional application of U.S. application Ser. No. 10/708,212 filed on Feb. 17, 2003 which claims the priority benefit of Taiwan application serial no. 92134517, filed on Dec. 8, 2003. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification.
- 1. Field of the Invention
- The present invention relates to an illumination control circuit. More particularly, the present invention relates to a pulse width modulation (PWM) illumination control circuit with low visual noise for driving a light-emitting diode (LED).
- 2. Description of the Related Art
- In recent years, conventional cathode ray tubes (CRT) are gradually being replaced by liquid crystal displays (LCD) due to big improvements in the semiconductor manufacturing techniques. LCD has many advantages over CRT including lower power consumption, a lighter weight, a higher resolution, higher degree of color saturation and a longer service life. For these advantages, LCD is being widely used in many electronic products including digital cameras, notebook computers, desktop monitors, mobile phones, personal digital assistants (PDA), car television, global positioning systems (GPS), palm-top game player, electronic translators and even digital watches and so on.
- In general, a liquid crystal display uses an array of light-emitting diodes (LED) driven by a simple driving circuit to serve as the light source. However, due to the special properties of an LED, brightness of the LED is not linearly related to the driving current. Furthermore, color of the LED may also vary according to the driving current. Hence, for a liquid crystal display that uses LED as a back light or illumination system, difficulties are often encountered when the illumination is varied by directly adjusting the driving current.
- To avoid the difficulties of illumination adjustment through an amplitude variation of the driving current, a constant amplitude driving current is used with illumination adjustment achieved through a pulse width modulation (PWM) of the driving current. Ultimately, the LED is able to produce consistent emitting efficiency within a broad range.
-
FIG. 1 is a block diagram of a conventional pulse width modulation illumination control circuit.FIG. 2 is a diagram showing the relationships between illumination control pulse signals and light-emitting diode driving current signals for the circuit inFIG. 1 . InFIG. 1 , an illumination control pulse signal Con that set the illumination of the light-emitting diode is sent to a DC/DC converter 110 to produce a light-emitting diode driving current signal Id for driving a light-emitting diode. The waveform diagrams (a), (b) and (c) inFIG. 2 represent three different pulse width settings of the light-emitting diode driving current signals Id. For example, the light-emitting diode is at full illumination (100%) inFIG. 2 (a), at 20% of the full illumination inFIG. 2 (b) and at 50% of the full illumination inFIG. 2 (c). - To prevent any perceived flickering in the light-emitting diode by the human eyes, the frequency of the illumination control pulse signal Con cannot be too low, typically above 200 Hz. In other words, the illumination control pulse signal Con must operate at a sufficiently high frequency so that the human eyes can retain a visual image and yet perceive a steady change of illumination without flickering. Obviously, these control signals may be implemented using a simple switching circuit that controls the on/off states of the entire DC/DC converter.
- Because the frequency and duty cycle of the aforementioned illumination control pulse signal Con is set to be fixed according to the required illumination, interference with the vertical, horizontal scanning signals may occur when used as back light in a liquid crystal display. The difference in frequency between the back light and the video signals often leads to the so-called ‘fanning effect’, a watery wave pattern of the image on a display screen. In addition, the switching on or off of the DC/DC converter also leads to a significant loading on the power supply that provides power to the DC/DC converter. In other words, a ripple waveform synchronized with the illumination control pulse signal Con is also produced in the power supply. Once again, the ripple waveform may affect the video display signals leading to a flickering screen.
- To prevent interference between the illumination control pulse signal Con and the vertical, horizontal scanning signal due to the frequency difference, the illumination control pulse signal Con and the horizontal scanning signals are synchronized to a frequency an integral multiple of each other. However, this arrangement will increase the production cost. To reduce the ripple waveform in the power supply, the frequency of the illumination control pulse signal Con can be increased. Yet, increasing the frequency of pulse signal Con leads to higher power consumption. With the demand of a larger display screen and a lesser visual noise, fabricating a light-emitting diode illuminated liquid crystal display with low noise and broad adjustable range of illumination is increasingly difficult.
- Accordingly, one objective of the present invention is to provide a pulse width modulation (PWM) illumination control circuit with low visual noise for driving a light-emitting diode (LED). By varying the duty cycle or frequency of an illumination control pulse signal and maintaining an average duty cycle and frequency, visual noise interference due to pulse width modulation is reduced.
- To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a low visual noise pulse width modulation illumination control circuit for controlling the illumination of light-emitting diodes inside a liquid crystal display. The low visual noise pulse width modulation illumination control circuit comprises an illumination control pulse generating unit and a DC/DC converter. The illumination control pulse-generating unit receives an illumination-adjusting signal. According to the illumination-adjusting signal, the illumination control pulse-generating unit generates an illumination control pulse signal having a duty cycle set to vary within a predetermined range. The DC/DC converter is coupled to the illumination control pulse-generating unit so that the illumination control pulse-generating unit can drive the light-emitting diodes according to the illumination control pulse signal.
- In one embodiment of the invention, the illumination control pulse-generating unit of the low visual noise PWM illumination control circuit further comprises a noise generator, an analogue adder and a comparator. The noise generator generates a noise signal. The analogue adder is coupled to the noise generator for receiving the illumination-adjusting signal and the noise signal to produce a noise signal loaded illumination-adjusting signal. The comparator is coupled to the analogue adder for comparing the noise signal loaded illumination-adjusting signal with a triangular wave and producing the illumination control pulse signal.
- In one embodiment of the invention, the noise signal level produced by the low visual noise PWM illumination control circuit can be adjusted.
- The present invention also provides an alternative low visual noise pulse width modulation illumination control circuit for controlling the illumination of light-emitting diodes inside a liquid crystal display. The low visual noise pulse width modulation illumination control circuit comprises an illumination control pulse generating unit and a DC/DC converter. The illumination control pulse-generating unit receives an illumination-adjusting signal. According to the illumination-adjusting signal, the illumination control pulse-generating unit generates an illumination control pulse signal having a frequency set to vary within a predetermined range. The DC/DC converter is coupled to the illumination control pulse-generating unit so that the illumination control pulse-generating unit can drive the light-emitting diodes according to the illumination control pulse signal.
- In one embodiment of the invention, the operations carried out by the illumination control pulse-generating unit of the low visual noise PWM illumination control circuit are implemented using a microprocessor.
- In one embodiment of the invention, the phase of the illumination control pulse signal produced by the low visual noise PWM illumination control circuit also varies within a predetermined range.
- Accordingly, the present invention provides a low visual noise PWM illumination control circuit for driving light-emitting diodes such that visual noise interference due to pulse width modulation is reduced by varying the duty cycle or frequency of an illumination control pulse signal and maintaining an average duty cycle and frequency.
- It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
- The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The following drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
-
FIG. 1 is a block diagram of a conventional pulse width modulation illumination control circuit. -
FIG. 2 is a diagram showing the relationships between illumination control pulse signals and light-emitting diode driving current signals for the circuit inFIG. 1 . -
FIG. 3 is a block diagram of a light-emitting diode low visual noise PWM illumination control circuit according to one preferred embodiment of the present invention. -
FIG. 4 is a circuit diagram of an illumination control pulse-generating unit according to the preferred embodiment of the present invention. -
FIG. 5 is a diagram showing the waveform of the illumination control pulse signal produced by the illumination control pulse-generating unit shown inFIG. 4 . -
FIG. 6 is a flow chart showing the steps for operating the illumination control pulse-generating unit according to the preferred embodiment of the present invention. - Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
-
FIG. 3 is a block diagram of a light-emitting diode low visual noise PWM illumination control circuit according to one preferred embodiment of the present invention. The low visual noise pulse width modulation (PWM)illumination control circuit 300 inFIG. 3 is adapted to control the illumination level of light-emitting diodes (not shown) inside a liquid crystal display. The low visual noise PWMillumination control circuit 300 comprises an illumination control pulse-generatingunit 310 and a DC/DC converter 320. The illumination control pulse-generatingunit 310 is used for receiving an illumination-adjusting signal Ref. According to the illumination-adjusting signal Ref, the illumination control pulse-generatingunit 310 generates an illumination control pulse signal Con. To improve the visual noise interference of pulse width modulation, the duty cycle or frequency of the illumination control pulse signal Con is permitted to vary within a predetermined range. Hence, differential frequency interference between a fixed illumination control pulse signal Con and the vertical/horizontal scanning signal leading to the so-called ‘fanning effect’ with wavy lines on the display screen is prevented. In addition, the DC/DC converter 320 drives the light-emitting diodes according to the illumination control pulse signal Con generated by the illumination control pulse-generatingunit 310. -
FIG. 4 is a circuit diagram of an illumination control pulse-generating unit according to the preferred embodiment of the present invention. As shown inFIG. 4 , the illumination control pulse-generatingunit 400 comprises anoise generator 410, ananalogue adder 420 and acomparator 430. Thenoise generator 410 further comprises aresistor 411 and anamplifier 421 electrically connected together and theanalogue adder 420 further comprises a plurality ofresistors amplifier 421 electrically connected together. Thenoise generator 410 outputs a noise signal Nos after theamplifier 412 inside thenoise generator 410 amplifies the thermal noise produced by theresistor 411. The noise signal Nos is transmitted to theanalogue adder circuit 420 such that the noise signal Nos and an illumination-adjusting signal Ref originally set to control the output duty cycle of the DC voltage are summed together to produce a noise signal loaded illumination-adjusting signal Ref. Theresistor 422 is a variable resistor so that the level of the noise signal Nos loaded on the illumination-adjusting signal Ref can be adjusted. The noise signal loaded illumination-adjusting signal Ref is transmitted to thecomparator 430 where the signal is compared with a triangular wave Tri to produce an illumination control pulse signal Con having a duty cycle that varies within the acceptable noise signal level as shown inFIG. 5 . - As shown in
FIG. 5 , although the duty cycle of the illumination control pulse signal Con varies on each transient moment of each cycle, the average power of the noise is zero. Hence, the average duty cycle of the entire circuit after adding the noise is identical to one without adding any noise. In other words, the illumination of the light-emitting diodes after adding noise to the circuit is identical to the illumination without adding any noise to the circuit. -
FIG. 6 is a flow chart showing the steps for operating the illumination control pulse-generating unit according to the present invention. When the illumination control pulse-generatingunit 310 as shown inFIG. 3 is implemented using a microprocessor, the steps inFIG. 6 can be carried out to produce an illumination control pulse signal Con with a variable frequency so that visual noise interference due to pulse width modulation is reduced. - Assuming that the illumination control pulse signal Con in
FIG. 3 has a frequency F=1/T, where T is the cycle of the illumination control pulse signal Con, n illumination control pulse signals Con with different cycle time such as T0, T1, T2, . . . , Tn−1 such that (T0+T1+T2+ . . . +Tn−1)/n=T can be designed. Furthermore, the n illumination control pulse signals Con with different cycle time can be permuted to form a queue before turning each signal out sequentially. For example, ifsequence 0 is {T0, T1, T2, . . . , Tn−1},sequence 1 is {T0, T2, . . . ,} and so on, the n illumination control pulse signals Con with different cycle time may be arranged to form a list of K different non-repeatingsequence including sequence 0,sequence 1, sequence 2, . . . , sequence K−1. Thereafter, the steps depicted inFIG. 6 can be executed using the microprocessor so that illumination control pulse signals Con each having a different frequency are sequentially output. The operating steps of a digitally operated illumination control pulse-generating unit with a low visual noise level are explained as follows. - In step S610, variables I, J are set to 0. Thereafter, in step S620, the Ith illumination control pulse signal cycle in sequence J and the received illumination-adjusting signal are combined to produce an illumination control pulse signal. In step S630, a 1 is added to the variable I in preparation for retrieving the next illumination control pulse signal cycle in sequence J. In step S640, the value of I is checked to determine whether it is equal to n. When the value of I is not equal to n, the operation returns to step S620. However, if the value of I is equal to n, step S650 is executed to reset I to 0 and add 1 to the value of J in preparation for retrieving the first illumination control pulse signal cycle of the next sequence. Thereafter, step S660 is executed to determine whether the value of J is equal to K. When the value of J is not equal to K, the operation returns to step S620. On the other hand, if the value of J is equal to K, step S670 is executed to reset the value of J to 0 and return the operation to step S620.
- The steps carried out in aforementioned description assumes the existence of K sequences. However, anyone familiar with the technique may understand that the operation is greatly simplified when K is 1. In addition, the phase of the illumination control pulse signal generated in step S620 can be set to vary within a predetermined range so that an illumination control pulse signal with a wider frequency range is produced.
- It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
Claims (7)
1. A pulse width modulation illumination control circuit for controlling the illumination of light-emitting diodes inside a liquid crystal display, comprising:
an illumination control pulse-generating unit, for receiving an illumination-adjusting signal and generating an illumination control pulse signal according to the illumination-adjusting signal, wherein a frequency of the illumination control pulse signal varies with time within a predetermined range; and
a DC/DC converter, coupled to the illumination control pulse-generating unit for driving the light-emitting diodes according to the illumination control pulse signal.
2. The control circuit of claim 1 , wherein the illumination control pulse-generating unit is implemented using a microprocessor.
3. A pulse width modulation illumination control circuit for controlling the illumination of light-emitting diodes inside a liquid crystal display, comprising:
an illumination control pulse-generating unit, for receiving an illumination-adjusting signal and generating an illumination control pulse signal according to the illumination-adjusting signal, wherein a phase shift of the illumination control pulse signal varies with time within a predetermined range; and
a DC/DC converter, coupled to the illumination control pulse-generating unit for driving the light-emitting diodes according to the illumination control pulse signal.
4. An illumination control pulse generating device for receiving an illumination adjusting signal, the illumination control pulse generating device comprising:
a random signal generating unit, for generating a random signal;
a combine unit, coupled to the random signal generating unit for combining the random signal with the illumination adjusting signal to form a random signal combining illumination adjusting signal; and
a comparator, coupled to the combine unit for comparing the random signal combining illumination adjusting signal with a comparing signal to produce a illumination control pulse signal, wherein a frequency of the illumination control pulse signal varies with time within a predetermined range.
5. The illumination control pulse generating device of claim 4 , wherein the random signal generating unit is a noise generator.
6. The illumination control pulse generating device of claim 4 , wherein the combine unit is an analogue adder.
7. The illumination control pulse generating device of claim 4 , wherein the comparing signal is a triangular wave.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US11/623,326 US20070114949A1 (en) | 2003-12-08 | 2007-01-16 | Pwm illumination control circuit with low visual noise for driving led |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
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TW92134517 | 2003-12-08 | ||
TW092134517A TWI291311B (en) | 2003-12-08 | 2003-12-08 | PWM illumination control circuit with low visual noise for LED |
US10/708,212 US7183723B2 (en) | 2003-12-08 | 2004-02-17 | PWM illumination control circuit with low visual noise for driving LED |
US11/623,326 US20070114949A1 (en) | 2003-12-08 | 2007-01-16 | Pwm illumination control circuit with low visual noise for driving led |
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Application Number | Title | Priority Date | Filing Date |
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US10/708,212 Division US7183723B2 (en) | 2003-12-08 | 2004-02-17 | PWM illumination control circuit with low visual noise for driving LED |
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US20070114949A1 true US20070114949A1 (en) | 2007-05-24 |
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US10/708,212 Expired - Fee Related US7183723B2 (en) | 2003-12-08 | 2004-02-17 | PWM illumination control circuit with low visual noise for driving LED |
US11/623,326 Abandoned US20070114949A1 (en) | 2003-12-08 | 2007-01-16 | Pwm illumination control circuit with low visual noise for driving led |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
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US10/708,212 Expired - Fee Related US7183723B2 (en) | 2003-12-08 | 2004-02-17 | PWM illumination control circuit with low visual noise for driving LED |
Country Status (4)
Country | Link |
---|---|
US (2) | US7183723B2 (en) |
JP (1) | JP3861091B2 (en) |
KR (1) | KR100598932B1 (en) |
TW (1) | TWI291311B (en) |
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US20070013339A1 (en) * | 2005-07-15 | 2007-01-18 | Delta Electronics Inc. | Motor control method and device thereof |
DE102009026612A1 (en) | 2009-05-29 | 2010-12-02 | Robert Bosch Gmbh | Method for controlling LED string, in display-backlight of motor vehicle, involves generating output signal during reaching of threshold value, and initiating generation of new threshold value, where signal determines clock pulse |
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WO2016085631A1 (en) * | 2014-11-26 | 2016-06-02 | Applied Materials, Inc. | Control architecture for devices in an rf environment |
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Families Citing this family (32)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP3800415B2 (en) * | 2002-07-30 | 2006-07-26 | ミネベア株式会社 | Pulse width modulation circuit and lighting device using the same |
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Citations (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6150771A (en) * | 1997-06-11 | 2000-11-21 | Precision Solar Controls Inc. | Circuit for interfacing between a conventional traffic signal conflict monitor and light emitting diodes replacing a conventional incandescent bulb in the signal |
US6150774A (en) * | 1997-08-26 | 2000-11-21 | Color Kinetics, Incorporated | Multicolored LED lighting method and apparatus |
US6567009B2 (en) * | 1999-12-28 | 2003-05-20 | Avix Inc. | Light control type LED lighting equipment |
US20030095406A1 (en) * | 1998-03-19 | 2003-05-22 | Ppt Vision, Inc. | Method and apparatus for a pulsed L.E.D. illumination source |
US20050156540A1 (en) * | 2003-12-16 | 2005-07-21 | Ball Newton E. | Inverter with two switching stages for driving lamp |
US7102340B1 (en) * | 2003-01-21 | 2006-09-05 | Microsemi Corporation | Dual-mode PFM boost converter |
US20060261756A1 (en) * | 2005-05-17 | 2006-11-23 | Kotaro Matsui | Discharge lamp lighting circuit |
US20080116820A1 (en) * | 2004-11-11 | 2008-05-22 | Minoru Ozasa | High-Pressure Discharge Lamp Lighting Device |
Family Cites Families (23)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH02147015A (en) * | 1988-11-29 | 1990-06-06 | Matsushita Electric Ind Co Ltd | Liquid crystal display device for cooker |
JP2770082B2 (en) * | 1990-12-13 | 1998-06-25 | 株式会社カイジョー | Light emitting device driving apparatus and method for use in image processing apparatus |
KR100306417B1 (en) | 1996-06-11 | 2001-11-30 | 윤종용 | Sound control circuit and method using microcomputer |
JPH10111487A (en) * | 1996-10-07 | 1998-04-28 | Yokogawa Electric Corp | Lcd back light driving circuit |
JPH1167471A (en) * | 1997-08-26 | 1999-03-09 | Tec Corp | Lighting system |
JP3951408B2 (en) * | 1998-02-09 | 2007-08-01 | ソニー株式会社 | Lighting device |
JP2000214825A (en) * | 1999-01-20 | 2000-08-04 | Nec Corp | Backlight display device and method |
WO2001005193A1 (en) * | 1999-07-07 | 2001-01-18 | Koninklijke Philips Electronics N.V. | Flyback converter as led driver |
JP2001308384A (en) * | 2000-04-20 | 2001-11-02 | Fujitsu General Ltd | Light-emitting element drive control system |
JP3529718B2 (en) * | 2000-10-03 | 2004-05-24 | ローム株式会社 | Light emitting device of portable telephone and driving IC therefor |
US6888529B2 (en) * | 2000-12-12 | 2005-05-03 | Koninklijke Philips Electronics N.V. | Control and drive circuit arrangement for illumination performance enhancement with LED light sources |
US7071762B2 (en) * | 2001-01-31 | 2006-07-04 | Koninklijke Philips Electronics N.V. | Supply assembly for a led lighting module |
JP3941411B2 (en) * | 2001-03-28 | 2007-07-04 | セイコーエプソン株式会社 | Light emission control device, electro-optical device, and electronic apparatus |
JP2002324685A (en) * | 2001-04-25 | 2002-11-08 | Sony Corp | Lighting device |
JP4043848B2 (en) * | 2001-06-28 | 2008-02-06 | 東芝松下ディスプレイテクノロジー株式会社 | LIQUID CRYSTAL DISPLAY DEVICE, ITS MANUFACTURING METHOD, AND LIGHTING DEVICE DRIVE CONTROL METHOD |
JP4068317B2 (en) * | 2001-07-27 | 2008-03-26 | Necディスプレイソリューションズ株式会社 | Liquid crystal display |
JP2003051394A (en) * | 2001-08-07 | 2003-02-21 | Denso Corp | Discharge lamp lighting device |
US6586890B2 (en) * | 2001-12-05 | 2003-07-01 | Koninklijke Philips Electronics N.V. | LED driver circuit with PWM output |
JP3685134B2 (en) * | 2002-01-23 | 2005-08-17 | セイコーエプソン株式会社 | Backlight control device for liquid crystal display and liquid crystal display |
KR100481214B1 (en) * | 2002-02-09 | 2005-04-08 | 엘지.필립스 엘시디 주식회사 | Apparatus and method of driving discharge tube lamp and liquid crystal display using the same |
EP1482770A4 (en) * | 2002-03-01 | 2007-01-03 | Sharp Kk | Light emitting device and display unit using the light emitting device and reading device |
KR100920353B1 (en) * | 2003-03-14 | 2009-10-07 | 삼성전자주식회사 | Device of driving light device for display device |
KR101026800B1 (en) * | 2003-11-21 | 2011-04-04 | 삼성전자주식회사 | Liquid crystal device, driving device and method of light source for display device |
-
2003
- 2003-12-08 TW TW092134517A patent/TWI291311B/en not_active IP Right Cessation
-
2004
- 2004-02-17 US US10/708,212 patent/US7183723B2/en not_active Expired - Fee Related
- 2004-02-26 KR KR1020040013065A patent/KR100598932B1/en not_active IP Right Cessation
- 2004-03-11 JP JP2004069392A patent/JP3861091B2/en not_active Expired - Fee Related
-
2007
- 2007-01-16 US US11/623,326 patent/US20070114949A1/en not_active Abandoned
Patent Citations (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6150771A (en) * | 1997-06-11 | 2000-11-21 | Precision Solar Controls Inc. | Circuit for interfacing between a conventional traffic signal conflict monitor and light emitting diodes replacing a conventional incandescent bulb in the signal |
US6150774A (en) * | 1997-08-26 | 2000-11-21 | Color Kinetics, Incorporated | Multicolored LED lighting method and apparatus |
US20030095406A1 (en) * | 1998-03-19 | 2003-05-22 | Ppt Vision, Inc. | Method and apparatus for a pulsed L.E.D. illumination source |
US6567009B2 (en) * | 1999-12-28 | 2003-05-20 | Avix Inc. | Light control type LED lighting equipment |
US7102340B1 (en) * | 2003-01-21 | 2006-09-05 | Microsemi Corporation | Dual-mode PFM boost converter |
US20050156540A1 (en) * | 2003-12-16 | 2005-07-21 | Ball Newton E. | Inverter with two switching stages for driving lamp |
US20080116820A1 (en) * | 2004-11-11 | 2008-05-22 | Minoru Ozasa | High-Pressure Discharge Lamp Lighting Device |
US20060261756A1 (en) * | 2005-05-17 | 2006-11-23 | Kotaro Matsui | Discharge lamp lighting circuit |
Cited By (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20070013339A1 (en) * | 2005-07-15 | 2007-01-18 | Delta Electronics Inc. | Motor control method and device thereof |
US7323838B2 (en) * | 2005-07-15 | 2008-01-29 | Delta Electronics, Inc. | Motor control method and device thereof |
CN102239745A (en) * | 2008-12-12 | 2011-11-09 | 密克罗奇普技术公司 | Three-color rgb led color mixing and control by variable frequency modulation |
DE102009026612A1 (en) | 2009-05-29 | 2010-12-02 | Robert Bosch Gmbh | Method for controlling LED string, in display-backlight of motor vehicle, involves generating output signal during reaching of threshold value, and initiating generation of new threshold value, where signal determines clock pulse |
WO2016085631A1 (en) * | 2014-11-26 | 2016-06-02 | Applied Materials, Inc. | Control architecture for devices in an rf environment |
CN107041167A (en) * | 2014-11-26 | 2017-08-11 | 应用材料公司 | Control framework for the device in RF environment |
US9872341B2 (en) | 2014-11-26 | 2018-01-16 | Applied Materials, Inc. | Consolidated filter arrangement for devices in an RF environment |
US10820377B2 (en) | 2014-11-26 | 2020-10-27 | Applied Materials, Inc. | Consolidated filter arrangement for devices in an RF environment |
US10820378B2 (en) | 2014-11-26 | 2020-10-27 | Applied Materials, Inc. | Consolidated filter arrangement for devices in an RF environment |
CN111917673A (en) * | 2014-11-26 | 2020-11-10 | 应用材料公司 | Control architecture for devices in an RF environment |
US11870252B2 (en) | 2014-11-26 | 2024-01-09 | Applied Materials, Inc. | Consolidated filter arrangement for devices in an RF environment |
US10074299B2 (en) | 2015-07-28 | 2018-09-11 | Microsoft Technology Licensing, Llc | Pulse width modulation for a head-mounted display device display illumination system |
Also Published As
Publication number | Publication date |
---|---|
US20050122060A1 (en) | 2005-06-09 |
JP3861091B2 (en) | 2006-12-20 |
US7183723B2 (en) | 2007-02-27 |
KR20050055577A (en) | 2005-06-13 |
TW200520621A (en) | 2005-06-16 |
JP2005173523A (en) | 2005-06-30 |
TWI291311B (en) | 2007-12-11 |
KR100598932B1 (en) | 2006-07-10 |
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