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EP-4280819-B1 - LED COLOR AND BRIGHTNESS CONTROL APPARATUS AND METHOD

EP4280819B1EP 4280819 B1EP4280819 B1EP 4280819B1EP-4280819-B1

Inventors

  • CHENG, DONGJIE
  • HUGAR, Vijay
  • BHAT, SUMIT
  • DAS, Joy

Dates

Publication Date
20260513
Application Date
20230424

Claims (12)

  1. A light emitting diode color and brightness control apparatus comprising: a bandgap voltage reference (VG) configured to generate a current reference for controlling a plurality of light emitting diode channels; a transistor (M1) coupleable in series to a cathode of a light emitting diode channel (D1) of the plurality of light emitting diodes channels; a first operational amplifier (A1); a plurality of MOSFET devices (MG1, MG2, MG3, MG4) connected in parallel and couplable between the cathode of the light emitting diode channel (D1) and ground through a source of the transistor (M1), wherein the plurality of MOSFET devices (MG1, MG2, MG3, MG4) is configured to control a current flowing through the light emitting diode channel; a control circuit (300) configured to generate gate drive signals for the plurality of MOSFET devices (MG1, MG2, MG3, MG4), wherein the gate drive signals are configured to adjust the current flowing through the light emitting diode channel based on a predetermined color and a predetermined brightness level of the light emitting diode channel; a current mirror having inputs coupled to the bandgap voltage reference (VG) through the first operational amplifier (A1); a set resistor (R SET ) coupled to the current mirror; a current-to-voltage conversion device coupled to an output of the current mirror; a second operational amplifier (A2), wherein an output of the second operational amplifier is coupled to a gate of the transistor (M1); and a sample and hold circuit (302) coupled between the output of the current mirror and a non-inverting input of the second operational amplifier (A2), wherein the first operational amplifier (A1) is configured to apply the bandgap voltage reference (VG) to the set resistor (RSET) to generate a first reference current (I), the current mirror is configured to convert the first reference current (I) into a second reference current (Iref), the current-to-voltage conversion device is configured to convert the second reference current (Iref) into a first reference voltage (Vref1), the sample and hold circuit is configured to provide the first reference voltage (Vref 1) to the non-inverting input of the second operational amplifier (A2), the second operational amplifier (A2) being configured to generate a second reference voltage (Vref 2) equal to the first reference voltage (Vref1) at an inverting input thereof, thereby applying the second reference voltage (Vref2) to a common drain of the plurality of MOSFET devices (MG1, MG2, MG3, MG4).
  2. The light emitting diode color and brightness control apparatus of claim 1, wherein: the set resistor (R SET ) is configured to determine a maximum current flowing through the transistor (M1).
  3. The light emitting diode color and brightness control apparatus of claim 1, wherein: the current mirror comprises a first current mirror transistor (MP1) and a second current mirror transistor (MP2) having gates connected together and further connected to an output of the first operational amplifier (A1); the first current mirror transistor (MP1) and the set resistor (R SET ) are connected in series between a bias voltage (V b ) and ground; an inverting input of the first operational amplifier is connected to the bandgap voltage reference (VG); a non-inverting input of the first operational amplifier (A1) is connected to a common node of the set resistor (R SET ) and the first current mirror transistor (MP1); the current-to-voltage conversion device comprises an auxiliary transistor (M2) connected in series with the second current mirror transistor (MP2) between the bias voltage (V b ) and ground, and wherein a gate of the auxiliary transistor is connected to the bias voltage; the non-inverting input of the second operational amplifier (A2) is connected to the output of the current mirror through the sample and hold circuit (302), the output of the current mirror comprising a common node of the auxiliary transistor (M2) and the second current mirror transistor (MP2); the inverting input of the second operational amplifier (A2) is connected to the source of the transistor (M1); and the plurality of MOSFET devices (MG1, MG2, MG3, MG4) comprises a first MOSFET device group (MG1), a second MOSFET device group (MG2), a third MOSFET device group (MG3) and a fourth MOSFET device group (MG4) connected in parallel between the source of the transistor (M1) and ground.
  4. The light emitting diode color and brightness control apparatus of claim 3, wherein: the sample and hold circuit (302) comprises a first switch (S1), a second switch (S2), a third switch (S3) and a capacitor (C0), and wherein: the first switch (S1) is connected between the common node of the auxiliary transistor (M2) and the second current mirror transistor (MP2), and the non-inverting input of the second operational amplifier (A2); the second switch (S2) and the third switch (S3) are connected in series between the common node of the auxiliary transistor (M2) and the second current mirror transistor (MP2), and the inverting input of the second operational amplifier (A2); and the capacitor (C0) is connected between the non-inverting input of the second operational amplifier (A2) and a common node of the second switch (S2) and the third switch (S3).
  5. The light emitting diode color and brightness control apparatus of claim 3 or 4, wherein: the first MOSFET device group (MG1) is configured to be controlled by a first global dimming control signal having 24 control bits, and wherein under the first global dimming control signal, the first MOSFET device group (MG1) is configured to provide a bleed current for compensating a finite amount of time used for charging the gate of the transistor (M1) from a low voltage potential to a high voltage potential.
  6. The light emitting diode color and brightness control apparatus of claim 3 or 4, wherein: the first MOSFET device group (MG1) is configured to be controlled by a first global dimming control signal having 24 control, and wherein under the first global dimming control signal, the first MOSFET device group (MG1) is configured to provide a bleed current for keeping the transistor (M1) to operate in an on state.
  7. The light emitting diode color and brightness control apparatus of claim 3 or 4, wherein: the first MOSFET device group (MG1) is configured to be controlled by a first global dimming control signal having 24 control bits, and wherein under the first global dimming control signal, the first MOSFET device group (MG1) is configured to provide a bleed current for compensating a duty cycle loss caused by the sample and hold circuit (302).
  8. The light emitting diode color and brightness control apparatus of any one of claims 3 to 7, wherein: the second MOSFET device group (MG2) is configured to be controlled by a second global dimming control signal having 6 control bits, and wherein under the second global dimming control signal, the second MOSFET device group (MG2) is configured to provide a delay compensation current for compensating a delay caused by a voltage change on the gate of the transistor (M1).
  9. The light emitting diode color and brightness control apparatus of any one of claims 3 to 8, wherein: the apparatus further comprises a PWM generator (304) configured to generate a PWM signal; and MOSFET devices in the third MOSFET device group (MG3) are configured to be selectively enabled by a third global dimming control signal having 6 control bits, and wherein under the third global dimming control signal, the enabled MOSFET devices in the third MOSFET device group (MG3) are configured to provide a PWM current flowing through the transistor (M1) based on the PWM signal.
  10. The light emitting diode color and brightness control apparatus of any one of claims 3 to 9, wherein: the fourth MOSFET device group (MG4) is configured to be controlled by a trimming control signal having 6 control bits, and wherein under the trimming control signal, the fourth MOSFET device group (MG4) is configured to adjust a current flowing through the transistor (M1) so as to balance currents flowing through different channels.
  11. The light emitting diode color and brightness control apparatus of claim 10, wherein: the apparatus is configured to receive the trimming control signal through a digital interface for adjusting the current flowing through the transistor (M1).
  12. A system comprising: a plurality of lighting modules (101, 112), each of which comprises a red light emitting diode channel (D0, D33), a green light emitting diode channel (D1, D34) and a blue light emitting diode channel (D3, D35); and a light emitting diode color and brightness control apparatus (100) according to any preceding claim: wherein the bandgap voltage reference (VG) is configured to generate a current reference for controlling the plurality of lighting modules.

Description

TECHNICAL FIELD Embodiments of the invention are related to a light-emitting diode color and brightness control apparatus and method, and more particularly, to an RGB based LED system. BACKGROUND A light-emitting diode (LED) is a semiconductor light source. When a voltage is applied to the LED, a current flows through the LED. In response to the current flowing through the LED, electrons and holes recombine in the PN Junction of the diode. In the recombination process, energy is released in the form of photons. The photons with different wavelengths and/or frequencies produce different colors of light. The primary LED colors are red, green and blue (RGB). Mixing these colors in different proportions can make almost all the colors of visible light. To produce a different color, three RGB colors in different intensities are combined. The intensity of light produced by an LED is proportional to the current flowing through the LED. The current flowing through the LED can be adjusted to change the intensity of the LED, thereby achieving a different color through changing the intensities of the RGB colors. An RGB based LED system plays a critical role in lighting technologies, which are widely used in fields such as automotive/industrial/architectural lighting, smart home appliances, wearable and handheld devices and the like. An RGB based LED system may comprise a plurality of RGB modules (e.g., 12 RGB modules). Each RGB module contains three light-emitting diodes, namely a red LED, a green LED and a blue LED. In most lighting applications, lights emitted from one RGB module are perceived by human eyes as a single point light source because of proximity of the three light-emitting diodes within one RGB module. The three RGB colors of one RGB module are mixed into a single color and a single brightness level. The color and the brightness level of the RGB module can be changed through adjusting the currents flowing through the three light-emitting diodes in the RGB module. A variety of colors can be created by mixing the three RGB colors in different light emission intensity ratios of red, green and blue. The brightness level of an RGB module is the total emission intensity from the three light emitting diodes combined. The brightness level of a channel (a light-emitting diode) is proportional to the average current flowing through the LED channel. The control process of an LED average current or emission intensity is often termed as dimming. The dimming process can be divided into two categories: analog dimming and PWM (pulse-width modulation) dimming. In the conventional RGB control methods, two complex control schemes are employed to control the color and the brightness level of the RGB based LED system. In a first RGB control method, a brightness PWM control scheme is applied to all RGB modules. In other words, the brightness and color of each RGB module are controlled separately. This is a partition control scheme. In a second RGB control method, a single functional control bit is used to control the color and the brightness level of a corresponding RGB module. This is a bundling control scheme. Either the partition control scheme or the bundling control scheme causes a complex and expensive system. Such a complex and expensive system has many shortcomings such as lack of design flexibility, poor reliability and the like. It would be desirable to have a simple control apparatus and method to effectively control the color and brightness level of an RGB based LED system. US 6095661A describes a flashlight and corresponding method. The flashlight includes a housing, a plurality of LEDs, and an electrical circuit that selectively applies power from the DC voltage source to the LED units. In one embodiment, the first electrical circuit further includes a control circuit for maintaining a predetermined light output level of the LED units as a charge on a battery varies. In another embodiment, the control circuit maintains an average predetermined light output level of the LED units as the charge on the battery cell varies by changing a pulse width or frequency as the charge on the battery cell varies. Another aspect provides an illumination source that includes a light-emitting diode (LED) housing including one or more LEDs, and a control circuit that selectively applies power from a source of electric power to the LEDs. Still another aspect provides an illumination source including a light-emitting diode (LED) housing including one or more LEDs; and a control circuit that selectively applies power from a source of electric power to the LEDs. US 2008/0315773 A1 describes an LED driving circuit that may control current flow into an LED on a current path according to the amount of light sensed from the LED. An LED driving circuit for driving at least one LED may include at least one of: An optical sensor for receiving light emitted from the LED and generating a feedback signal having a level corresponding to an amoun