High-brightness LED lighting color mixing scheme based on Cypress's EZ-Color controller

introduction

With the ever-changing pace of the semiconductor lighting industry, high-bright LEDs with long life, low energy consumption, flexible application, environmental protection and other advantages are gestating a new industrial revolution - the lighting revolution, making our lives and work The environment is glamorous and colorful. However, since the LED itself is a characteristic of a semiconductor device, LED lighting design faces two major challenges - LEDs of the same color have various types of specifications and the performance of the LED is lowered with temperature. This requires lighting engineers to make LED model specifications and temperature compensation considerations when designing LED lighting color mixing. LED model specifications and temperature compensation algorithm design are not only complex, but also require lighting engineers to have a more professional knowledge of color theory. This has led many lighting design engineers to avoid complicated LED model specification compensation algorithm design by designing and producing LEDs with specified specifications. But this will bring an increase in cost to the entire system, because LED suppliers usually charge an additional 10% of the designation fee. In order to help the majority of lighting design engineers solve the challenge of LED color mixing design, this paper introduces a Cypress-based EZ-Color controller that does not require the specification of LED models, and can quickly and easily complete a high-performance LED lighting with excellent performance. Color mixing design.

EZ-Color controller

The EZ-Color controller is a programmable system-on-chip chip from Cypress for high-brightness LED lighting color mixing applications. It is mainly composed of 8-bit microprocessor, programmable analog module and digital module, plus hardware multiply accumulator, I2C, Flash, SRAM and other peripheral peripheral modules, as shown in Figure 1.

Figure 1: Functional Block Diagram of the EZ-Color Controller

Therefore, in addition to the calculation control function of the general LED color mixing system, the EZ-Color controller can flexibly realize the required analog and digital peripheral functions according to the specific requirements of the color mixing system through programmable analog and digital modules. For example, the EZ-Color controller CY8CLED16 with 16 programmable digital modules can be integrated to realize the LED lighting color mixing system of up to 16 LED control channels. It can also be designed as a 32-bit resolution 4-channel LED control channel. Color mixing system. In order to facilitate the user to achieve high-brightness LED color mixing design simply and quickly, Cypress built a three-color LED color mixing module based on EZ-Color controller and codeless design software. This color mixing module has been configured with PSoC internal registers, programmable module internal wiring, LED model specifications and temperature compensation algorithm software. When users need to design the lighting color mixing system, just select the three-color LED color mixing driver as the windows operation and drag and drop it into the PSoC express design area. All the lighting color mixing software will be automatically generated.

Realization of high-brightness LED lighting color mixing scheme

Implementation mechanism of color mixing scheme based on PSoC express

EZ-Color's high-brightness LED lighting color mixing design is based on Cypress's codeless graphical design software, PSoC express. When the user wants to complete the design of a system, it is only necessary to perform simple operations. The first step is the input and output driver selection; the second step is to define the behavior relationship or transfer function relationship between the output and the input. The EZ-Color color mixing scheme is no exception. It is also composed of input, output drive and transfer function relationships, as shown in Figure 2.

Figure 2: EZ-Color solution implementation mechanism diagram

As can be seen from the above implementation mechanism diagram, EZ-Color's LED color mixing scheme uses (x, y, Y) to represent the input, and the output is RGB three-color LED. The hardware driver of the three-color LED uses SSDM (random signal strength). Modulation) User Module. The input (x, y, Y) is the color input request information of EZ-Color according to the characterization method of CIE 1931 chromaticity diagram, that is, x, y represents hue and color saturation, and reflects chromaticity information of color, and Y Represents luminous flux and reflects the brightness information of the color. The SSDM User Module is a hardware implementation of Cypress's PrISM (Precision Signal Strength Modulation) technology. PrISM technology is Cypress's proprietary LED brightness adjustment technology, which effectively solves electromagnetic interference and low frequency flicker problems.

PrISM technology

Conventional LED brightness control is achieved by using a pulse width modulated signal (PWM signal), which is adjusted by changing the aspect ratio. This method of brightness adjustment is simple, but since the PWM signal is a signal that is fixed at high and low levels, its harmonic components are very rich and electromagnetic interference is large. At the same time, when the low-frequency PWM signal is used for brightness control, the human eye will notice that the light is blinking.

The brightness control of the EZ-Color solution uses Cypress's proprietary PrISM technology. Compared with the PWM control method, it can effectively solve the electromagnetic interference and low frequency flicker problems. As shown in Figure 3, the PrISM technology compares the random counter with the value of the signal strength register required by the user. If the value in the random counter is less than the signal strength value, the high level signal is output, and when it is large, the output is low. The level, which produces a precise illumination pulse signal with a random variation of high and low width.

Figure 3: Block diagram of the implementation of PrISM technology

The precise illumination signal with randomly varying high and low level widths makes the intensity pulse signal non-periodic. The direct benefit of the aperiodicity of the pulse signal is that the spectrum of the signal is continuous and small in amplitude, as shown in Figure 4. At the same time, the PrISM high and low level signals are randomly changed, so there is no low frequency flicker problem that can be perceived by the human eye due to the slow change of the low frequency PWM signal due to its high and low level signals.

Figure 4: Spectrogram of the PWM signal and the PrISM signal

PSoC express design and real-time debugging

PSoC express helps users simplify and intuitively complete the development and design of high-bright LED color mixing applications, online debugging capabilities. The following is an example of Cypress's EZ-Color development board RGB-3261A, which describes how to use PSoC express for color mixing design and debugging.

A. Open the PSoC express software and create and name a new project.

B. Select the Triple Luxeon K2 color hybrid drive from the High Brightness LED in the Output Drives list and drag it to the workspace (see Figure 5). After being released to the workspace, PSoC express will pop up an add output driver window. At this time, after inputting the drive ColorMixer as the HB LED driver name, click "ok".

Figure 5: Output Drive List

C. When the HBLED window appears, select “Thermistor Temporary Sensor” from the associated temperature sensor list (see Figure 6).

Figure 6: List of associated temperature sensors

D. Enter the attribute parameters of the selected sensor in the Temperature Sensor Properties window.

E. Set the LED model specifications for your choice, as shown in Figure 7. PSoC express software automatically generates the required temperature compensation and model specification compensation software according to the temperature sensor and LED model specification attribute parameter set by the user during compilation.

Figure 7: LED model specification parameter setting table

F. After setting the parameters of the HBLED driver, click OK.

G. Select four variables as input from the evaluator driver in express: LEDBrightness, LEDEnable, xValuator, yValuator; select I2C as the LED color mixing system from the interface driver to communicate with the external control system. interface.

H. Define the transfer function relationship between the output and the input: Right-click the "ColorMixer" output drive icon and select the transfer function to open the transfer function dialog. In the transfer function dialog box, the four variables as input can be configured in one-to-one correspondence with the four parameters of the output transfer function. Once configured, as shown in Figure 8, a connection line is displayed between the output and the input.

Figure 8: Output and Input

I. Compile the project and generate the code to burn. During the compilation process, PSoC express will pop up the device selection and pin configuration diagram. After the user makes the corresponding device selection and pin configuration according to the circuit board made by himself, click OK, PSoC Express will continue to complete the project compilation and construction work. After the project was built, the design work of a high-bright LED lighting color mixing system without writing a single line of code and based on the EZ-Color controller was basically completed.

J. Program burning. After the project compilation is completed, connect the program PSoC burner and click “PSoC programmer” to start the program K. Online real-time debugging. PSoC express can not only help users to intuitive graphical design, but also support online real-time debugging function, enabling users to input color request information in real time and observe the LED color mixing effect in real time, thus ensuring that the LED color mixing result achieves customer satisfaction. Let's take this design as an example to briefly describe how to easily implement online real-time debugging. The first step is to connect the PSoC express online real-time debugging hardware - I2USB board; the second step, click "monitor" from the PSoC express design area, enter the debugging window, and then click the I2USB board to run the button "Run"; the third step, right Click on the output driver "ColorMixer", select "show tuner", then the EZ-Color debug window opens, as shown in Figure 9. At this time, the user can click on the desired color in the chromaticity diagram to watch the color mixing effect in real time, and realize the online debugging function.

Figure 9: EZ-Color online real-time debugging window

Conclusion

The design is simple, easy to apply, and has excellent performance. It can be widely used in urban lighting, indoor and outdoor decoration, signal lights, stage lights and LED advertising screens to achieve accurate and consistent color output. (Text / Cypress senior application engineer Ai Xiaohui)

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