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  • Because LED has a series of advantages such as energy saving, long life, fast response, good color reducibility, mercury free and environmental protection requirements, it has replaced the traditional CCFL backlight and become the mainstream backlight for tft lcd display (LCD). Now in the application of large LCD display screen, LED backlight has gradually become the mainstream.

    Small size LCD LED backlight LCD screen, mainly used in mobile phones and digital cameras, and some industrial instruments use monochrome LCD module, the screen size of 3 ~ 7cm, with LED as backlight, as long as the use of 3 ~ 6 white LED, series or parallel can be.If a white LED flash is used in the same device, a larger driving current is required.Sometimes the backlight brightness is not fixed, but allows the user to adjust the brightness in white lines, which requires the driver to adjust the brightness (that is, change the driving current).Because this kind of demand is increasing, many analog integrated circuit, power management integrated circuit manufacturers to adapt to this demand, have developed and produced a variety of integrated circuit drive LED.

    This kind of circuit generally has the control function of LED backlight and LED flash, as well as the function of on and off control and multi-stage brightness control. It has strong functions but few external components.Many of the chips that drive leds that we will cover in the following sections fall into this category, and there are many suppliers and product models to choose from.Display devices with larger display sizes than mobile phones and digital cameras, such as personal digital assistant (PDA), portable media player (PMP), electronic dictionary, handheld game console, etc., have display sizes ranging from 9 to 10cm, and Max can also reach 18cm.

    Due to the current LED illumination is difficult to achieve uniformity in the large screen scope, so the size is no longer suitable to use multiple LED direct configuration to do the backlight, but to use a backlight module, in the backlight module, the use of refraction, light guide plate and other measures to make white LED illumination uniform, meet user requirements.PDA and PMP manufacturers buy these modules directly from backlight armour module vendors instead of using several leds to make up the backlight.However, in some designs, some people still use more leds (such as 8 to 10) to make backlight for larger LCD screens.

    LED backlight of medium size LCD screen is mainly used in portable DVD, notebook computer, car navigator and other equipment, such as 7-12 inches, the LED backlight adopted by them is developed on the basis of the drive scheme of LED backlight of small size LCD screen.Article USES the aluminum LED to replace the CCFL light source, the drive power supply shall be as far as possible with existing CCFL backlight driving power on the interface compatible with each other, with simple dc drives (with batteries, many for the 12 v power supply) to replace the complex ac drives, although its comprehensive cost is a bit expensive, but it is similar to the traditional CCFL backlight module.At this time, if multiple LED arrays are still used, due to the increase in the number of LED, the serial and parallel LED groups are generally considered as a whole, and the driving power is used to control its current and adjust its brightness.

    LED backlight of large LCD screen in the LED backlight of large LCD screen, it is possible to light up hundreds or more leds at the same time to provide sufficient brightness, which requires higher voltage, more current, more flexible control mode and more strict heat dissipation of the driving power.At the same time, also put forward higher requirements for the consistency of LED characteristics, the driver and LED current matching and flow sharing.The LED used should be strictly screened and classified according to the luminous wavelength and brightness of the LED.When testing LED optical properties and classifying parameters, most of them are based on consistent rated current value, and then give the allowable variation range of forward pressure drop.It is expected that large LED screen backlight will soon replace CCFL as a mainstream product.

    Backlighting has fully penetrated all sizes of LCD screens

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