Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K7/00—Modulating pulses with a continuously-variable modulating signal
  • H03K7/08—Duration or width modulation ; Duty cycle modulation
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/2007—Display of intermediate tones
  • G09G3/2011—Display of intermediate tones by amplitude modulation
• • 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
  • H05B45/12—Controlling the intensity of the light using optical feedback
• • 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
  • H05B45/14—Controlling the intensity of the light using electrical feedback from LEDs or from LED modules
• • 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
  • H05B45/395—Linear regulators
  • H05B45/397—Current mirror circuits
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2320/00—Control of display operating conditions
  • G09G2320/06—Adjustment of display parameters
  • G09G2320/0606—Manual adjustment
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2320/00—Control of display operating conditions
  • G09G2320/06—Adjustment of display parameters
  • G09G2320/0626—Adjustment of display parameters for control of overall brightness
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2360/00—Aspects of the architecture of display systems
  • G09G2360/14—Detecting light within display terminals, e.g. using a single or a plurality of photosensors
  • G09G2360/145—Detecting light within display terminals, e.g. using a single or a plurality of photosensors the light originating from the display screen
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/2007—Display of intermediate tones
  • G09G3/2014—Display of intermediate tones by modulation of the duration of a single pulse during which the logic level remains constant
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/2007—Display of intermediate tones
  • G09G3/2077—Display of intermediate tones by a combination of two or more gradation control methods
• • 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
• • 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 generally relates to display devices, and more particularly, to a method and apparatus for controlling luminance of light emitting display devices.
• the dashboard displays of modern transportation equipment automobiles, aircraft, ships, trains, even the space shuttle, etc., require efficient, uniform illumination in order to accommodate operation under low ambient lighting conditions, e.g., evening or nighttime hours.
• the illumination should be made variable and controlled manually or automatically via a closed-loop sensor controlled feedback system, to accommodate changes in available ambient light.
• Controls of the type aforementioned typically have an exponentially decaying power curve associated therewith. This non-linear effect causes the lamp to dim quickly at first, then at an ever-decreasing rate, as the rheostat is varied. Conversely, the lamp brightens very slowly at first and then suddenly becomes very bright. Neither of the foregoing situations is desirable, especially to an aircraft pilot. In an attempt to eliminate or dampen the aforedescribed situation, one solution may be to use an "audio taper" rheostat (exponentially varying resistive element) in conjunction with the lamps. However, these devices are expensive, difficult to obtain, and have very limited resistance ranges.
• Pulse width modulation is well known in the art and allows the lamps to be turned on and off at a set frequency utilizing a variable duty cycle: the duty cycle being defined as the ratio of the "on" time to the "total” time.
• the duty cycle can easily be varied from zero (fully off) to 100 per cent (fully on).
• the PWM technique provides a significant improvement over the variable series resistive element described above. It is very efficient, and virtually no power is dissipated in the control potentiometer. Pulse width modulation techniques are well known to those skilled in the art and will not be discussed here.
• the problem with the PWM technique although not as pronounced as with the series rheostat approach, is the non-linear output produced.
• the lamp power, or luminance is actually the root-mean-square (RMS) of the pulse train presented to the lamps.
• RMS root-mean-square
• the effective, or RMS, values of periodic waveforms are well known and will not be discussed herein. Suffice it to say that the lamp illuminates much faster than desired, and conversely, extinguishes much slower due to the non-linearity of the lamp power associated with the RMS values of the pulse train presented to the lamps.
• An apparatus for delivering linear power drive to a light source.
• the apparatus comprises a pulse width modulator responsive to a command voltage drive signal for providing a pulse width modulated signal at an output. The widths of the pulses and the frequency varying simultaneously as the command voltage drive signal is varied, and the output of the pulse width modulator being coupled to the light source.
• the apparatus also comprises a frequency control circuit responsive to the command voltage drive signal for supplying a control current to the pulse width modulator such that the frequency of the pulse width modulated output signal is varied.
• a method for delivering linear power drive to a light source comprises the step of providing a pulse modulation signal with the widths of the pulses thereof being varied in accordance with a command signal.
• the method comprises the step of varying the frequency of the pulse modulation signal simultaneously with the widths of the pulses being varied.
• FIG. 1 is a block diagram of pulse width modulation system usable in describing the instant invention.
• FIG. 2 is a block diagram of the pulse width modulation apparatus of the present invention for providing linear power drive control of luminance devices.
• the present invention provides linear power drive for controlling the luminance level of various displays including, but not limited to, incandescent lamps and light emitting diodes (LEDs) in a linear fashion.
• various displays including, but not limited to, incandescent lamps and light emitting diodes (LEDs) in a linear fashion.
• pulse width modulation circuitry 10 for controlling the current through lamp 12 such that the luminance thereof is linearly controlled in response to adjusting control potentiometer 14.
• a conventional pulse width modulator (PWM) integrated circuit 16 is used which is responsive to the voltage developed across potentiometer 14 for providing output current pulses for turning on lamp 12. The widths of these current pulses are varied as the voltage across potentiometer 14 is varied.
• Voltage controlled current source 18 is also responsive to the voltage developed across potentiometer 14 and provides a control signal to PWM 16 which in turns adjusts the frequency of the current pulses appearing at the output of PWM 16.
• novel drive circuitry 30 employing a pulse modulation technique for providing linear power to a load.
• the load is illustrated as a string of light emitting diodes (LEDs), represented by reference numeral 32, serially connected between a voltage source and the output of voltage controlled current source 34.
• Controlled current source 34 is gated on and off as driver FET 36 is turned on and off by pulse width modulator 16 the output of which is coupled to the gate of FET 36.
• a feedback network consisting of photodiode 38, transimpedance amplifer 40, and logarithmic amplifier 42 provides feedback to maintain the luminance of the LEDs set by a driving source command signal applied to input 44.
• photodiode 38 senses the luminance of one or more of lamps/LEDs comprising the string of diodes 32 and drives transimpedance amplifier 40 consisting of operational amplifier 46 and resistor 48.
• Transimpedance amplifier 40 provides a feedback voltage to the input of logarithmic amplifier 42 responsive to the photodiode current.
• Logarithmic amplifier 42 converts the voltage at its input to a logarithmic voltage that is combined with the driving source command signal at summing node 50.
• the composite signal at summing node 50 is applied to the input of integrator 52 which provides an integrated voltage at node 54 that is provided to controlled current source 34, and the pulse modulator circuitry comprising pulse width modulator 16 and frequency control circuit 56.
• Voltage controlled current source 34 provides the primary current control through LEDs 32. Thus, as the integrated composite voltage at node 54 is varied, the current flow through the LEDs is varied accordingly.
• the integrated composite voltage appearing at node 54 is applied across capacitor 58 and provides the control voltage to pulse width modulator 16 for varying the width of the modulation pulses supplied at the output of pulse width modulator 16 to the gate of control switch or FET 36.
• Frequency control circuit 56 converts the voltage developed across capacitor 58 into a representative current for driving the resistor input of pulse width modulator 16 which in turn varies the frequency of the pulses supplied to FET 36.
• drive circuitry 30 varies the pulse widths of the pulse width modulation load driving signal as well as simultaneously varying the frequency thereof responsive to the command signal applied to the circuitry. Hence, as the pulse width increases, so does the frequency of the PWM signal driving the load devices. Additionally, the current is also varied in response to the command signal and increases from low luminance to high luminance as the pulse widths and frequency of the load driving modulation signal increase. This results in a substantially linear power delivery to the load devices.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Computer Hardware Design (AREA)
• General Physics & Mathematics (AREA)
• Theoretical Computer Science (AREA)
• Circuit Arrangement For Electric Light Sources In General (AREA)
• Led Devices (AREA)
• Discharge-Lamp Control Circuits And Pulse- Feed Circuits (AREA)
• Electronic Switches (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (5)

Cited By (1)

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Citations (5)

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• 2002
  • 2002-10-28 US US10/282,892 patent/US6724158B1/en not_active Expired - Lifetime
• 2003
  • 2003-10-17 WO PCT/US2003/033190 patent/WO2004040759A1/en not_active Ceased
  • 2003-10-17 JP JP2004548398A patent/JP2006504245A/ja active Pending
  • 2003-10-17 AU AU2003284289A patent/AU2003284289A1/en not_active Abandoned
  • 2003-10-17 EP EP03776469.3A patent/EP1563604B1/en not_active Expired - Lifetime

Patent Citations (5)

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