Satisfying the demand for energy-efficient and aesthetically pleasing illumination.

By Nobuyuki Ikuta, Senior Design Engineer Manager at ROHM Semiconductor

Today, LEDs dominate the automotive lighting landscape because of their energy efficiency, long lifespan, and compact form factor. With newer automotive designs, the demand for custom, energy-efficient, and aesthetically pleasing illumination has driven a growing interest in RGB Chip LEDs. RGB Chip LEDs consist of three individual LED chips—Red, Green and Blue—in a single package. RGB LEDs are based on the primary color model.

By additive color mixing and adjusting each chip’s intensity, virtually any color in the visible spectrum (including White by combining Red + Green + Blue) can be created as required.

Conventional vs. RGB LEDs

Traditional automotive LED lights are typically monochromatic: they emit a single color. Conversely, RGB LEDs combine red, green, and blue emitters into one LED package. While standard LEDs are efficient, RGB polychromatic LEDs minimize energy consumption by utilizing only the necessary color spectrum for a given application.

RGB Chip LEDs can be integrated into onboard systems enabling colors to be varied, thereby delivering custom lighting and brand differentiation. The following section takes a deeper dive into the challenges posed by integrating the latest LEDs.

Dimming: Dimming is crucial in automotive applications for various reasons, e.g., reducing glare, adjusting to ambient lighting conditions, or enhancing aesthetics.

The prevalent technique for regulating the brightness of LEDs is Pulse Width Modulation (PWM) dimming. However, some products may flicker or not dim uniformly when subjected to PWM signals, leading to inconsistent lighting and potential safety hazards.

Voltage and Current Requirements: Another concern for designers and engineers transitioning to new LED technologies is differing power requirements. Depending on component selection, differing power requirements may lead to potential compatibility issues and necessitate modifications to existing electrical systems.

Heat Dissipation: While newer LEDs are significantly more efficient than their incandescent counterparts, they are not entirely free from producing heat. The localized heat generated at the LED junction needs to be effectively dissipated to ensure longevity. Inadequate heat management can result in reduced LED lifespan, color shift, and—in extreme cases—catastrophic failure.

Space Constraints: The compact and intricate design of modern vehicles poses challenges for engineers integrating LED products, and integrating efficientcooling systems like heat sinks may be impractical. Thus, achieving a balance between maintaining the vehicle’s aesthetic and ensuring proper thermal management is critical.

 

Color variation due to color mixing: ROHM RGB Chip LED vs. standard product

 

Key advantages of RGB LEDs

The following section presents key benefits of RGB LEDs for automotive illumination over traditional lighting solutions.

Energy Efficiency: Compared to traditional incandescent and halogen bulbs, RGB LEDs operate on lower voltages and currents. This efficiency results in reduced energy consumption and offers advantages in situations where battery or power resources are constrained.

Long Lifespan: The solid- state nature of RGB LEDs promotes their longevity. Unlike traditional bulbs, which rely on filament heating, RGB LEDs are less prone to failure from mechanical shock and vibration. With lifetimes up to 25 times longer than halogen bulbs, RGB LEDs require fewer replacements for end-users and offer significant cost savings in manufacturing and procurement for automakers.

Dynamic Color Range: Modulating the intensity of each RGB diode produces an immense variety of colors. This capability allows designers and engineers to differentiate lighting products through unique aesthetic features or functional indications.

Fast Response: The instantaneous response of RGB LEDs ensures critical functions are activated without delay, thereby enhancing driver and pedestrian safety. This feature is useful in applications where fractions of a second can be the difference between safe and unsafe scenarios.

Design Flexibility: The compact design of RGB LEDs allows for versatile integration, enabling sleeker designs and innovative light arrangements in automotive applications.

Thermal Management: Due to their efficient operation, RGB LEDs dissipate significantly less heat in space-constrained automotive applications. This advantage avoids the need for bulky heat sinks. Moreover, generating minimal heat minimizes the thermal strain on adjacent components. It is important to consider the total power dissipation of an LED when operating at higher ambient temperatures or when driving multiple chips in one package.

Dimming Capabilities: Embedded with microcontrollers, RGB LEDs can be programmed for adaptive lighting solutions, like adjusting the intensity based on ambient light. This feature is beneficial in applications like dashboard illumination, where the brightness needs to be adjusted based on external lighting conditions. With PWM, RGB LEDs achieve dynamic lighting effects, such as gradual illumination or color transitions, thereby enhancing the visual appeal.

Key considerations for RGB Chip LED/ Driver IC selection

Automotive LEDs must provide reliability, durability, and performance under varied conditions. To achieve this, engineers must consider electrical compatibility, thermal management, and specific automotive needs when selecting RGB LEDs and Driver ICs.

The following considerations support RGB LED selection:

• Luminous Efficacy: Refers to how much illumination LEDs provide for a given power input. Higher luminous efficacy offers more illumination for the same power consumption, thereby saving energy.

• Color Consistency: Refers to consistent color output, critical in applications such as dashboard illumination or ambient lighting. Color consistency also ensures aesthetic appeal and functional uniformity, especially when color changes indicate specific vehicle functions or alerts.

• Lifespan and Degradation: Refers to a LED’s loss of brightness with prolonged use. Selecting LEDs with minimal luminous degradation and long lifespans ensures longevity.

Key considerations for selecting LED driver ICs include the following:

  • Dimming Capabilities: Dimming capabilities that are smooth and free from flickering are useful in scenarios like night driving. LED driver ICs should support these requirements, accommodating PWM or analog dimming protocols.
  • Integration with Legacy Systems: Integrating with the intricate electrical systems in modern vehicles is vital for LED driver ICs, avoiding disruptions or requiring significant modifications.
  • Circuit Protection: Protecting circuits, given the vulnerabilities of components to electrical disturbances, requires in- built protective mechanisms for driver ICs. Overcurrent, short-circuit, LED open, and thermal shutdown are vital features that ensure LED and driver IC reliability.
  • Thermal Compatibility: Producing some measure of heat, RGB LEDs and driver ICs should work in tandem. Their combined thermal output must bewithin specified limits to ensure no overheating occurs, compromising the system’s lifespan or safety.

RGB Chip LED and driver

ROHM’s SMLVN6RGBFU RGB LED is specifically designed for automotive So interiors. It utilizes a proprietary element that greatly reduces chromaticity variations (ranks). This ability allows for precise color matching, making it ideal as a light source for automotive interior applications where image color is important, like function and status indicators in instrument clusters, Center Information Displays (CIDs), and accent lighting in areas such as footwells, door handles, roofs, cup holders, and more. The SMLVN6RGBFU RGB Chip LED delivers vibrant and accurate color representation, ensuring aesthetic appeal and functional utility.

With the SMLVN6RGBFU RGB LED, ROHM can provide calibration support by specifying the adjustment coefficients to target a specific rank, minimizing the color variation. This new RGB Chip LED and high-accuracy chromaticity simulation allows precise color matching between multiple LEDs.

High-Quality Color Representation: The SMLVN6RGBFU reduces color variation by precisely controlling the luminous characteristics of RGB elements, achieved through a vertically integrated production system from the element fabrication stage.

Extended Lifespan and Low Maintenance: The design and precise control of the RGB elements of the SMLVN6RGBFU ensure high- quality color representation and contribute to the extended lifespan of the LED.

Energy Efficiency: Efficient LED operation results in reduced power consumption, benefiting applications like electric vehicles, where energy usage directly impacts the vehicle’s range.

Ease of Integration and Compatibility: The SMLVN6RGBFU is compatible with a constant current or PWM output signal, simplifying integration and wiring in various vehicle components and systems.

Driver IC: ROHM’s BD2808MUV-M is an automotive-grade 24-channel constant current sink LED driver IC optimized for driving ROHM RGB LEDs. It offers a high output voltage capability and can control RGB LEDs with a 6-bit Current DAC for each color. Additionally, it integrates an 8-bit PWM control for each channel in a compact VQFN48MCV070 package. The BD2808MUV-M achieves precise control of LED brightness and color, ensuring consistent and reliable performance. With features like PWM dimming, this driver IC also helps to reduce power consumption.

Key applications

Inaccurate or inconsistent color representation can lead to misinterpretations, which could affect the safety and comfort of vehicle occupants. ROHM’s SMLVN6RGBFU RGB Chip LED ensures minimal chromaticity variation. The colors produced are consistent and match the intended design, enhancing the overall user experience. Key applications include ambient mood lighting in automotive interiors, controls (audio, HVAC…), and switches and interface systems.

Chromaticity simulation in ROHM’s RGB Chip LED

Conclusion

With their ability to produce a wide range of colors, RGB Chip LEDs offer myriad advantages in automotive lighting applications, surpassing the capabilities of traditional automotive LEDs and other light sources. Their color variety, compactness, energy efficiency, and enhanced safety features make them a great choice in modern vehicles. In the evolving landscape of automotive lighting, RGB LEDs will remain critical for bridging design and technological innovation.

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