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Posts Tagged ‘RGB’

Light Emitting and Brightness Control Principles of LEDs

20 Oct

1. What is an LED?

When the minority carrier injected into the PN junction of semiconductor material recombines with the majority carrier, the excess energy will be be released in the form of light, which directly converts electrical energy into light energy. When reverse voltage is imposed on PN junction, minority carrier is hard to be injected, it does not light. This kind of diodes which are manufactured by using the principle of injected electricity leading to lighting are called light emitting diodes, commonly known as LEDs.

2. How does an LED light?

The light color and light efficiency of an LED are related to the materials and workmanship used to manufacture LEDs, currently there are three kinds of LEDs, red, green and blue LEDs which are widely used. Since the working voltage of LEDs is low (only 1.5-3V), and LEDs emit light spontaneously and have a certain brightness, meanwhile the brightness can be adjusted through voltage (or current), LEDs themselves are shock resistant with a long lifetime (100,000 hours), so in large display device, currently there is no other display methods to compete with the LED display.

The display screen that use the pixel which is made by putting one red LED and one green LED together is called double color display or color display; the display screen that use the pixel which is made by putting one red LED, one green LED and one blue LED together is called tricolor display or full color display. The pixel size of indoor LED screens is generally 2-10 mm, which often uses the method of packaging several kinds of LEDs that can can emit different primary colors as an entire body, The pixel size of outdoor LED screens is generally 12-26 mm, each pixel consists of several different single color LEDs, the finished product is called pixel tube, and double color pixel tube usually consists of 3 red LEDs and 2 green LEDs, tricolor pixel tube typically consists of 2 red LEDs, 1 green LED and 1 blue LED.

Whichever kind of screen we use LEDs to make, single color, double color or tricolor screens, to display images, the brightness of every LED that composes the pixel shall be adjustable, and the adjustable degree is the gray scale of the screen. The higher the gray scale is, the more delicate the displayed image is, the more rich the colors are, the corresponding display control system is also more complex. Generally color transition of 256-level gray scale images is already very smooth, while the color transition of 16-level gray scale color images has obvious boundary line. Therefore, the current color LED screen are required to make as 256-level gray scale.

3. Methods to control LED brightness:

There are two methods to control the LED brightness.

1). Take advantage of human beings’ visual inertia and use a pulse width modulation method to achieve gray scale control, which is cyclically changing the pulse width (ie duty ratio), as long as the repeated cycle of lighting is short enough (ie refreshing frequency is high enough), the human eyes can not feel the jittering of light-emitting pixels. Because PWM is more suitable for digital control, and the dispaly content of LED screens is supplied by micro computers, almost all of the LED screens use pulse width modulation to control the gray scale.

2). Changing the current that flows through the LEDs, generally LED tube allows a continuous working current of around 20 mA, except that red LEDs have saturation phenomenon, other LEDs’ brightness is basically proportional to the flowing current.

LED control system usually consists of main control box, scan board and display and control device. The main control box gets the brightness data of different color LEDs in one pixel from the computer’s graphics card and reassigns them to several pieces of scan board, each scan board is responsible for controlling several rows (columns) on the LED screen, and the display and control signals of each row (column) on the LED screen and control signals are transferred with serial manner. There are two serial transfer methods to transfer display and control signals: one is that the pixel gray scale is controlled collectively on the scan board, the scan board decomposes the brightness value of each pixel from the control box. (ie pulse width modulation), then transfer the opening signals of the each row LEDs to the corresponding LEDs with pulse mode and in serial manner (1 for lighting up, 0 for not lighting up) and control whether to light it up or not. This way uses a small quantity of components, but the amount of serial transfer data is large, because in a repeated cycle of lighting, each pixel with 16-level gray scale requires 16 pulses, with 256-level gray scale requires 256 pulses, due to the device working frequency restrictions, this method can only achieve a 16-level gray scale for LED screen.

Another way is that the content that the scan board transfers in serial manner is not the openning or closing signals for each LED but a 8-bit binary brightness value. Each LED has its own pulse width modulator to control the lighting time. Thus, in a repeated cycle of lighting, each pixel under the 16-level gray scale requires only 4 pulses, and under 256-level gray scale requires only 8 pulses, which greatly reduces the frequency of serial transfer. Using this decentralized control method to control LED gray scale can easily achieve 256-level gray scale control.

 

Remote RGB controller with speed

30 Mar

Remote RGB controller with speed

Key Features

Stores and plays 16 different pre-programmed color patterns Can manage the color pattern or speed over the remote or set the parameter on the controller by pressing button “MODE” or “SPEED

Features & Benefits

Widely used as a adjuster to control the color changing effects, it is suitable for LED Strips light, LED Module and so on. 
Deft™ FRC-V100 Remote Controller is an enhanced hardware controller to drive low-voltage RGB products, such as Signage™ blocks, Linear™ Ribbon, Cove™ neon and ropes.
Deft™ FRC-V100-L stores and plays 16 different pre-programmed color patterns.  It adopts PWM (pulse width modulation) technology, at 315KHZ frequency; it enables you to manage the color pattern or speed over the remote (in standard selling package). You can also set the parameter on the controller by pressing button “MODE” or “SPEED”.

Data | Specifications

Working voltage 12V DC (100W), 24V DC (200W)
Current:8A
Dimension:L130*W60*H35mm
Weight:190g

Applications

It is suitable for low-voltage RGB products such as LED Strips light& LED Module.

 
 
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