HB LED Color-Mixing Kit with Temperature Compensation

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Temperature-dependence and binning requirements for high brightness LEDs, high power LEDs and organic LEDs (OLEDs), present designers with unique challenges. Fast time-to-market and precision color control require flexible evaluation hardware with a built-in feedback loop and binning intelligence for color compensation.

Rising junction temperature degrades an LED’s luminous flux and modifies the dominant wavelength. Figure 1 shows how actual LEDs react to temperature changes. It is not a pretty picture, especially for Red.

 

 

Until recently, compensation for this reduction in luminous intensity was not trivial. Engineers essentially have to use a thermistor or temperature sensor and then implement some form of a two or three dimensional lookup table to adjust the dimming waveform accurately. The thermistor itself must be located as close to the LEDs as possible in order to read the board temperature and utilize an approximation equation for the junction temperature of the LEDs.

The second challenge, until recently, has been the variance of particular LEDs, even of the same part number. LEDs are “binned” according to their luminous flux, dominant wavelength, and forward voltage. The difference of a single dominant wavelength bin can be noticeable to the human eye. Again, multi-dimensional lookup tables have to be created, since the designer will not know which bin he will receive until the reel arrives at the production floor. To make matters even worse, bin definitions vary from LED manufacturer to LED manufacturer, so additional software lookup tables have to be created for multiple brands of LEDs. For a premium, customers can receive particular bins to avoid these variances and assure themselves of a fixed color point.

 

The Solution

The new Cypress EZ-Color™ HB LED Controller Evaluation Kit (CY3261A-RGB) and PSoC Express 3.0 software tool solve both of these challenges. They build in temperature feedback, enabling designers to simulate and build flexible colormixing applications with accurate color compensation for varying LED junction temperature. Express 3.0 also makes it easy to adjust for binning variations at the system level via a CIE 1931 color space. The pre-defined LUXEON® High Power LED drivers in Express 3.0 intelligently assure constant color output, enabling designers to customize for particular LED bins with minimal software overhead.

After building the design and programming the EZ-Color device on the board, a designer can use the PSoC Express 3.0 Monitor for precision color control. This includes a graphical tool called the “Tuner,” which creates the CIE chart with gamut dependent on the LED bins selected in the Properties menu. Using the Cypress CY3240-I2USB adapter, the designer can then adjust the intensity and color interactively within the PSoC Express 3.0 visual development environment. Adding an external color sensor such as a Konica-Minolta CL200, the designer can test the produced mixed color. Another tuning option is to override the manual feature and let the program free-run, where the cursor will move with the color dependent on user-specified logic.

The EZ-Color CY3261A-RGB board further ensures output accuracy by driving a constant current into its LUXEON® K2 High Power LEDs using National Semiconductor’s inductor-based step-down converter, the LM3402, which is specifically designed for LED driving. (However, any power converter that is able to have a dimming waveform as an input can be used.)

The EZ-Color™ CY3261A-RGB kit comes with seven colors preprogrammed into the onboard CY8CLED16 EZ-Color HB LED Controller. The board is accompanied by a CD containing a standalone color selector software application (used with the included USB cable), PSoC Express 3.0 (with the color selector integrated), PSoC Programmer, and a suite of documents, schematics and firmware examples. A Cypress CY3217 kit or standard Mini- Prog and cable are required to program the board.

To help you get started quickly, the CY3261A-RGB kit and PSoC Express 3.0 software contain several example projects, including:

3-LED Color Mixing with Tuner Over I²C

This project creates the EZ-Color™ firmware that color mixes three primary high-brightness LEDs to a target color on the 1931 CIE XYZ color space. The system enables turning ON/OFF the LEDs, adjusting the relative flux output and specifying a target pair of color coordinates on the 1931 CIE XYZ color space. Using PSoC Express’s monitor mode, all of these commands are communicated to EZ-Color™ over an I²C interface. Interface (Communication) Valuators (transfer function variables that process input data) map the LED Enable, LED Brightness and xy coordinates from I²C to the color mix driver. In turn, EZ-Color™ drives the LM3402 switching regulators to power the LEDs.

 

3-LED Color Mixing with State Machine

This example project builds on the previous project by adding a state machine. The state machine feeds into a set of priority encoders, which work like valuators except the values change depending on the input, which controls the inputs of the color mixing driver. The mixed color output of this project follows a path around the chromaticity chart. The Express Example Project documentation on the CY3261A-RGB kit CD contains detailed instructions for building these projects.

 

Conclusion

An HB LED color-mixing evaluation board should ideally provide temperature feedback and constant current drive to maximize color accuracy. The Cypress EZ-Color CY3261A-RGB kit, combined with PSoC Express 3.0 software provides these plus LED-specific drivers with binning compensation. Adding the CY3240-I2USB adapter allows for real-time color monitoring and tuning, significantly cutting development time and simplifying implementation of color-mixing LED applications.

 

PSoC Express™ software allows for the complete design of color-mixing systems in just 5 EZ steps

PSoC Express software with lighting specific drivers can significantly cut development time and simplify implementation of fixed color points through temperature and LED binning compensation.

 

Get started today and see how easy accurate color-mixing can be with the Cypress EZ-Color evaluation board. Future Electronics and Cypress are currently holding EZ-Color seminars throughout the world. Learn how to use EZ-Color kits and PSoC Express 3.0 software in all sorts of color-mixing applications. Details on the Salt Lake City Seminar Details on the San Jose Seminar

 

FEATURES Flexible integration Up to 16 configurable LED channels 8-32 bits of dimmer resolution LED control plus battery charging, motor control and more. Compatible with I2C, SPI, UART, DMX512 and DALI network protocols Precision color control Binning compensation Temperature compensation All-in-one software Breakthrough low frequency and EMI performance PrISM™ technology Easy-to-use tools Drag and drop designs Minimal coding required

APPLICATIONS Architectural and general lighting Entertainment and stage lighting Signage City beautification Intelligent lighting Landscape Backlighting Retail display

 

 

Control Type	Overview	Applications
Color Mixing with Temperature Feedback	Design tools with built-in LED binning compensation for improved color accuracy Temperature compensation algorithm for color maintenance Color selection made easy with PSoC Express Create networked designs using multiple protocols	Architectural lighting, signage, entertainment lighting
Color Mixing with Optical Feedback	Optical compensation algorithm for color maintenance Multiple communication interfaces enable interface with any optical sensor Create networked designs using multiple protocols	Architectural lighting, signage, LCD backlight
Dimming	Configurable analog and digital blocks allow simple integration PrISM Modulation Technology reduces radiated EMI Up to 32-bits of dimmer resolution	Camera/handset flash, flashlights, indicator lights, architectural lighting, signage, entertainment lighting

 

 

 

 

 

EZ-Color Evaluation Kit

The CY3261A-RGB board is a preprogrammed HB LED color mix board with seven pre-set colors using the CY8CLED16 EZ-Color HB LED Controller. The board is accompanied by a CD containing the color selector software application, PSoC Express 3.0 Beta 2, PSoC Programmer, and a suite of documents, schematics, and firmware examples.

The color selector software application can be installed on a host PC and is used to control the EZ-Color HB LED controller using the included USB cable. The application enables you to select colors via a CIE 1931 chart or by entering coordinates.

 

 

“MiniProg” Programmer

The MiniProg provides a simple to use and cost effective programming solution that is superb for a development environment. It consists of a USB interface to the development PC and a 5-pin header that is used to connect to the target board. It works in conjunction with the GenProg software available through download as part of the PSoC Designer tools on the Cypress website. The MiniProg can also be used in conjunction with the CY3216 to program devices out-of-system, or with the CY3655-PLG to program enCoRe II devices through the USB connector.

The CY3217 kit consists of the same programmer that is available in the PSoC CY3210-MiniProg1, but provided as a stand-alone item without the PSoC evaluation board. This kit is an ideal item to enable quick turn programming at multiple development/test sites.

The CY3217 “MiniProg” USB Programmer includes:

• (1) MiniProg programmer board
• (2) Std-A to Mini-B USB cable

 

 

I²C to USB Bridge Debugging/Communication Kit

The I²C to USB Bridge is a quick and easy link from any design or application’s I²C bus to a PC via USB for design testing, debugging and communication. The bridge is based on 1 of Cypress’ CY8C24894, which contains 6 analog blocks supporting ADCs, DACs and filters, 4 digital blocks supporting PWMs, timers and counters and a full-speed USB 2.0 peripheral.

 

 

 Featured Products

Part Number		Description	Data Sheet	App. Notes
CY3217		"MiniProg" Programmer Kit
CY3240-I2USB		I2C to USB Bridge Debugging/Communication Kit
CY3261A-RGB		EZ-Color Evaluation Kit
CY8CLED04-68LFXI		PSoC LED EZ-Color Drives 4 LEDs
CY8CLED08-48LFXI		PSoC LED EZ-Color Drives 8 LEDs
CY8CLED08-48PVXI		PSoC LED EZ-Color Drives 8 LEDs
CY8CLED16-28PVXI		PSoC LED EZ-Color Drives 16 LEDs
CY8CLED16-48LFXI		PSoC LED EZ-Color Drives 16 LEDs
CY8CLED16-48PVXI		PSoC LED EZ-Color Drives 16 LEDs

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