Why we need high PWM for the pixel led strip?
When we learn the IC chip specs, we always note there are two important rates, one is named refresh rate, another important parameter is PWM rate. These two above rates can be important in certain venues, such as broadcast activity.
Considering on there are many version IC chips for LED series products like UCS2904,WS2812b, APA107, HD107S,DMX512 etc, today let’s talked these two rates concepts in context.
Refresh rate can be a confusing specification, and is often confused with frame rate. But frame rate is generally a property of the incoming source material like the IC chips material, rather than the display.
Here we talked refresh rate is the frame rate concept in LED pixel solution.
What’s the LED Pixel’s refresh rate ?
Refresh rate refers to the maximum speed at which all the pixels can be updated per second. It can also be interpreted as how many times per second the pixels are able to draw a new image. It is usually measured in frames per second (FPS) which is different with the refresh rate refers to the display that is usually quantified in hertz ( HZ ).
Each frame is a not dynamic image, and displaying frames in rapid succession creates the illusion of motion.
From this concept, we can see the faster refresh rate results in smoother, the quicker and dynamic changes to the pixel to create more realistic effect you could imagine.
The higher frames per second (fps), the smoother the displayed motion will be. The slower refresh rate might be result in content that doesn’t look as smooth as it should be.
What determines the refresh rate in LED pixel system?
There are many factors that contribute to the overall refresh rate. The most significant of these factors are:
Refresh rate is affected by several factors, all of which contribute to the overall refresh rate. The most significant of these factors are:
- IC chip model which contains refresh rate ,the grayscale, data speed and so on.
- Efficiency of the software like Lededit, MADRIX, Arduino, Raspberry Pi, and what refresh rate the software can achieve.
- Processing time of the controller you choose.
- The controller load capability.
So, we can understand easily via the following image.
From the picture we can see the data is transmitted by the sending software like Lededit, Raspberry pi, Arduino and MADRIX, then it is processed by the network, then the LED controller, and the pixel leds finally.
So, from the sending software through to the pixel leds, these all steps can affect the overall refresh rate.
What’s the PWM in LED Pixel?
Pulse Width Modulation, or PWM, is a method for getting results with digital means. Digital control is used to create a waveform, a signal turned between on and off rapidly.
The duration of “on time” is called the pulse width. Changing the portion of the time the signal spends on and the time that the signal spends off by altered by the IC chips, allowing the LEDs to spend a specific amount of time between turning on and off quickly.
While the IC chips receive the data to dim the LED itself, they regularly using this PWM method. LEDs are ran by this square wave to switch a signal between on and off rapidly that control over the average current and voltage delivered to the load. Each LED can generate a PWM signal, telling each LED what color and how bright it should be.
Overall, PWM signals are in use for dimming LEDs brightness that maintain specific characteristics of the LED, for example, efficiency, color, or color temperature.
What affect PWM rate in LED Pixels?
The rate at PWM signal repeated is called the PWM rate. PWM rate is a fixed value that is totally determined by the type of IC chips you are choosing. No matter what incoming data you sent, the PWM is generated at a fixed frequency by the each IC pixels. That means the IC chip is the only factor that would affect PWM rate.
This chart is for the popular IC chips for reference.
| Pixel Model | Resolution | PWM rate | Refresh Rate | Clock Type | RGB | RGBW |
| APA102 | 8 bits | 1.9KHZ | 60fps | Clocked |  | |
| APA107 | 8 bits | 9KHZ | 60fps | Clocked | | |
| HD107S | 8 bits | 27KHZ | 260fps | Clocked | | |
| HD108 | 16 bits | 27KHZ | 260fps | Clocked | | |
| GS8208 | 8 bits | 8.0KHZ | 260fps | Single data | | |
| SK6805 | 8 bits | 1.2KHZ | 40fps | Single data | | |
| SK6812 | 8 bits | 1.2KHZ | 40fps | Single data | | |
| SK6813 | 8 bits | 1.2KHZ | 40fps | Single data | | |
| SK9822 | 8 bits | 4.6KHZ | 150fps | Clocked | | |
| SK9826 | 16bits | 4.6KHZ | 70fps | Clocked | | |
| SM16703 | 8 bits | 1.2KHZ | 40fps | Single data | | |
| SM16704 | 8 bits | 1.2KHZ | 40fps | Single data | | |
| TM1814 | 8 bits | 1.0KHZ | 30fps | Single data | | |
| UCS1903 | 8 bits | 1.8KHZ | 50fps | Single data | | |
| UCS1904 | 8 bits | 1.5KHZ | 50fps | Single data | | |
| UCS2903 | 8 bits | 1.6KHZ | 50fps | Single data | | |
| UCS2904 | 8 bits | 1.8KHZ | 60fps | Single data | | |
| UCS2909 | 8 bits | 1.8KHZ | 30fps | Single data | | |
| UCS2912 | 8 bits | 1.8KHZ | 30fps | Single data | | |
| UCS512C4 | 8 bits | 3.6KHZ | 120fps | A,B data | | |
| WS2801 | 8 bits | 2.5KHZ | 80fps | Clocked | | |
| WS2811 | 8 bits | 400 HZ | Single data | | ||
| WS2812B | 8 bits | 400 HZ | Single data | | ||
| WS2815 | 8 bits | 2.0KHZ | 60fps | Single data | |
As started, both refresh rates and PWM rates are the important factors in certain venues, such as broadcast activity.
