Determine PWM Values This is How Precise Color Mixing And Adaptive Lighting With LEDs Succeed

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Würth Elektronik eiSos GmbH & Co. KG

Wuxi InfiMotion Technology Co., Ltd.

The free developer tools on the Würth Elektronik online platform REDEXPERT have a new addition: With the ICLED Color Calculator, PWM values can be determined to display specific color values with ICLEDs. The basis is the parameters that the manufacturer determines for each batch of its pixel LEDs with integrated IC before they leave the warehouse.

Carlos Roberto Hernández Gómez is Product Manager Optoelectronics at Würth Elektronik eiSos.

Grouping red, green, and blue LEDs into pixels and using additive color mixing to represent any color opened up new possibilities for displays and lighting designs. From ambient lighting systems to audio and gaming devices, signal systems, displays on charging stations, and full-color matrix displays, powerful solutions can be realized by using adjacent red, green, and blue LEDs as pixels instead of the pixels of an LCD.

The approach becomes particularly interesting with ICLEDs. These components, also known as addressable, smart, or pixel LEDs, are LED packages that include an integrated circuit (IC). This driver enables the individual control of the red, green, and blue chips in the package through pulse-width modulation (PWM), allowing for sophisticated and precise lighting solutions with various colors. Since each pixel color can be individually regulated in brightness from 0 to 100 percent and digitally dimmed, the integrated RGB LEDs can produce more than 16 million different color and brightness values (based on the current standard of 8-bit depth).

And since fewer components, such as resistors, are needed, display solutions with the intelligent LEDs are not only faster to implement but also more energy-efficient than traditional LEDs. Digital control increases the flexibility of what can be displayed. Instead of being limited to a few pre-set circuits, any texts or symbols can be displayed.

Efficient LED Dimming Through Pulse-Width Modulation

The simplest method for controlling the brightness of LEDs is dimming via current intensity. However, this can alter the color value, which is often undesirable. In contrast, pulse-width modulation (PWM) in pixel LEDs with an integrated circuit (IC) enables precise "dimming" by turning the current on and off in extremely fast intervals that are imperceptible to the human eye.

In practice, control is carried out via data signals generated by a microcontroller (MCU). These signals are sent through a data line to the DIN pin of the first ICLED in the circuit. Additional components are connected in a so-called daisy-chain configuration (Figure 1). Each integrated circuit (IC) in the ICLED reduces the received data packets by its own, for example, 24 bits, and forwards the remaining data bits to the next LED in the chain (Figure 2).

If the DIN pin of the first ICLED detects a reset code, it signals the start of a new data packet transmission. This method ensures that each LED can be controlled precisely and independently without any color changes. This technique represents a significant advancement for electronics developers aiming to implement sophisticated lighting applications.

PWM Control And Color Calibration of LEDs

The frequency of pulse-width modulation (PWM) determines the brightness of each individual red, green, and blue LED in a pixel LED system. These frequency combinations create different color values in additive color mixing. With knowledge of the specific frequency that leads each LED to a desired color value and brightness, developers can produce a wide color palette. However, application developers have so far encountered a significant problem: accurately determining these frequencies has been a challenge, as manufacturers provided little support in this area.

Additionally, the challenges were exacerbated by the varying color reproduction of LEDs, even within the same shipment. Even the smallest deviations in materials or production processes can lead to noticeable performance differences, despite the components being considered identical. This issue highlights the need for precise calibration techniques and closer collaboration between manufacturers and developers to achieve consistent and reliable results in LED control.

From Quality to Binning

Würth Elektronik entered the ICLED market late and had to differentiate itself through quality and service. For its ICLEDs, available in six designs, the manufacturer placed particular emphasis on high-quality manufacturing, such as gold coatings for chip LEDs and silver coatings for PLCC versions, to improve solderability. Comparative measurements with pin-compatible competing models showed 40 percent higher luminous intensity.

A bothersome issue during assembly was also addressed: unlike comparable solutions currently available on the market, the smart LEDs feature a moisture sensitivity level of MSL3, instead of the usual MSL5 or MSL5a. To qualify the LEDs for various applications, the manufacturer provides photobiological test reports according to EN 62471:2008 and IEC 62471:2006 for all models in the product group. These are required by customers needing to assess potential risks to eye safety from light sources, such as in consumer products, lighting solutions, or medical devices. The tests and qualifications are conducted based on the guidelines of AEC Q102-003.

Since deviations are unavoidable even with good manufacturing practices, Würth Elektronik introduced particularly strict binning to ensure customers can rely on consistent performance. For quality assurance, all LEDs are 100 percent electrically and optically tested after production. They are then sorted into groups based on brightness and color. This binning ensures that the LEDs on a reel are largely uniform. The luminance tolerance is currently ± 5% per color per batch. For color location, the current products feature a tolerance of ± 0.005 for the xy color coordinate values in the CIE 1931 color space per color.

If controlling ICLEDs allows the selection of 16 million color and brightness values, it should also reliably be possible to reproducibly apply a specific color uniformly to a group of LEDs. Uniformity is achieved through strict binning. To achieve the desired color tone, there is the ICLED Color Calculator.

Individual Color Values With 8-Bit

The ICLED Color Calculator significantly expands the possibilities for lighting and signal solutions with ICLEDs. With this service, developers can, for the first time, easily determine the necessary programming specifications to represent a specific color value. On the intuitive user interface of the REDEXPERT ICLED Color Calculator (Figure 3), customers select the desired ICLED type as well as the color and brightness in the CIE1931 standard color system ("xy color space"). This automatically generates the appropriate digital value for the pulse-width modulation of the RGB LEDs integrated into the ICLED component, based on the characteristics of their bin. These values can be directly incorporated into the ICLEDs' programming. The generated color values for PWM control can also be exported to an Excel file. Additional export formats can be added based on customer requirements. A future version is expected to include an API for automated tool integration.

Currently, the tool provides PWM values with 8-bit depth, corresponding to 256 levels and thus meeting the common industry standard. However, the architecture is already designed to allow an extension to 12-bit, which is planned for version 2 of the tool.

The fact that the frequencies used by ICLEDs for PWM signals vary is irrelevant for the ICLED Color Calculator, as the tool ensures the reproducibility of a targeted color per batch. For example, the very common PLCC 4 version in the 5050 form factor operates at 4 kHz, while the PLCC 6 5050 Dual type operates at 20 kHz. Using the part and batch numbers, you can obtain the respective RGB values for control, which, for instance, produce the Würth Red, corresponding to the coordinate point x = 0.6408 and y = 0.33 in the CIE1931 color space.

Flexibility And Openness in Focus

When developers work with ICLEDs from Würth Elektronik, numerous possibilities are available. With controllers such as Arduino Uno, Adafruit Feather M0, Raspberry Pi, or ESP32, a wide range of platforms is offered for their projects. Würth Elektronik's provided Software Development Kit (SDK) supports quick software integration. A comprehensive set of tools can be found on the company's website, including platform-independent drivers and example applications. The latter are written in C and C++ and developed with Visual Studio to ensure seamless integration.

In case certain ICLEDs are not yet included in the Online Calculator, Würth Elektronik provides the raw data for the respective batch upon request via email. This approach promotes open and versatile data availability, independent of specific systems or applications. The goal is to offer developers maximum freedom and flexibility to effectively implement their projects.

Functions for Optimizing ICLED Developments

Currently, Würth Elektronik's tool focuses on the precise calculation of PWM values for color mixing in the CIE 1931 color space. Although gamma corrections are important for visually or color-critical applications, their integration into the tool is still in the evaluation phase. Developer feedback is appreciated to determine whether and how this feature should be added in the future.

Another planned feature is temperature compensation. The ICLED Color Calculator is currently based on measurements at 77 °F. Future updates aim to account for temperature drift, as it can affect color accuracy. For applications with high LED density, effective cooling—whether passive or active—is recommended to ensure a consistent thermal environment. This minimizes color drift and ensures stable, color-accurate results.

ICLEDs enrich the portfolio beyond conventional analog LEDs and specifically address a wide range of market requirements. Particularly in demanding applications in signal technology or for optical effects, they offer decisive advantages. Thanks to their high precision in control, which Würth Elektronik has enabled through accurate color reproduction, new fields of application are opening up, such as in adaptive lighting or color-coded signal applications. (heh)

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