Where is lcd backlight

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This is a preview of subscription content, log in to check access. Figure 1 a shows the bottom-light structure. Because of its high-luminance feature, the bottom-light structure is commonly used for PC monitors and TVs. With regard to the luminance uniformity on an LCD panel, a light-mixed zone is necessary between the diffusion plate and the light sources.

This zone causes undesirable thickness for large-sized TV applications. Figure 1 b shows the hollow type structure in which an LGP is used to reduce the thickness of the light-mixed zone. The good qualities of this type pertain to its compact shape, high luminance and good thermal dissipation. Figure 1 c shows the edge-light structure commonly used in a small-scale LCD panel. This type is of compact shape and low power consumption, so it is suitable for notebook PCs and personal digital assistant PDA products.

Simple driving feature make it as a popular choice for new generation of LCD backlight sources in portable display products. Its color filter divides the emitted white light into RGB sub-pixels to present color pictures. Thicknesses of RGB sub-pixels must be adjusted according to the corresponding wavelengths to correct the white balance on LCD panel.

This results in the difficulty of manufacturing process. The white-color point may vary after a long working time. Thus, the RGB LEDs mixing three-color lights to white light are more suitable for medium-scale, or even large-size screens [ 10 - 16 ].

The LCD TV power provides a 12V output for the signal-process board, a 24V output for the backlight driving circuit and an additional 5V standby-power output. As shown in Figure 3 , the backlight driving circuit consists of three power converters.

Therefore, dimming control is an important design consideration for LED backlight applications. We studied three dimming methods for current regulation of the parallel connected LED arrays: the transconductance-amplifier TA dimming, the current-mirror CM dimming and the burst-mode BM dimming.

Figure 4 a shows the TA dimming circuit. The LED current can be expressed as Equation 1. Figure 4 b shows the CM dimming circuit.

The LED current can be expressed as Equation 2. However, the conduction losses of the dimming transistors will be difficult to solve [ 17 ]. An adaptive voltage output for the DC-DC converter is usually designed to retain the minimum drain-source voltage on the dimming transistors. Considering the switching loss for the dimming transistors, the burst-mode frequency f b is designed at Hz that are unperceivable to the human eye.

The duty ratios of the dimming transistors are varied to regulate the LED average current that can be represented as Equation 3. The dimming transistors are operated as low-frequency switches, the thermal problem on the dimming transistors can be improved significantly. The current variations can be minimized by using the TA or BM dimming methods while the CM dimming has the simplest circuit configuration.

Anyway, the TA and CM dimming methods are unsuitable to be used in the high-power LED backlight design of LCD panels due to the significant conduction losses of the dimming transistors under dimming operations. The luminance of the red light is always highest and the luminance of the blue light is lowest among three color lights. In practical applications, the blue light is most sensitive to human eyes such that lower luminance of blue LED is enough to compose white light with the red and green LEDs.

The characteristic impedance and the resonant frequency are respectively [ 18 - 21 ]. List of Partners vendors. Briley S. His work is featured at Ideaing, Smartwatches. Twitter LinkedIn. Updated on September 30, Tweet Share Email. LED Backlit. Full LED. How do I know if my monitor uses LED backlighting? Was this page helpful? Thanks for letting us know!

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