White light-emitting diode backlight design art of war

White light-emitting diode (White Light-Emitting Diode; WLED, often written as: White LED) emerges, the LED lights can only be used to get rid of the last number, neon ornaments and other occasions, began to electronic lighting into the field, including the automotive direction assist lamp, elementary digital camera flash, etc. have been able to replace the WLED, what is more, the industry will have the WLED die area increased manufacturing, from 2 × 2mm increase to 5 × 5mm, enhance its luminescence so WLED also be used in the car on the main lamps, can only be considered for approval by the market.
In addition, WLED also a popular application, that is to serve as the LCD backlight to replace the previous CCFL (Cold Cathode Fluorescent Lamp; CCFL). However, at this stage will be used WLED backlight has its benefits also has its victims, how to take benefits Nourishing, will be of concern to designers of electronic engineering.
Generally, mobile phones, digital cameras (preview window) and other attachment devices are among a small LCD display size, such as 2.2 ", 2.5", etc., and some clamshell phone also has sub-display, sub-display over Main screen much smaller, about more in the 1.2 "or so, the number of these small inch WLED LCD if using as its backlight, simply will 36 WLED (depending on the screen using the number of pieces depending on the size) can be series-parallel implementation.
WLED addition to doing mobile phones, digital camera's LCD backlight can also have other outside use, such as today's phones in the button will glow in the dark for the convenience of users dialing (keypad backlight), or call the antenna area will glow tips These are also available WLED, with another entry-level digital cameras or camera phones, have begun to act with WLED flash (about 14), so in a single device to use more pieces of WLED, components and consistent increase in the amount of in the design and manufacture of benefits on both the supply schedule.
Although a small number of the LCD backlight inch simply and string, WLED arrangement 36 can, but further two questions: 1. If the same type of device has WLED flash, the flash light to a higher drive current than even need to have pre-flash (red-eye reduction). (2) the brightness of the backlight is not static, sometimes thoughtful design energy-saving mode, the power-saving mode automatically reduces the backlight brightness, or allow users to adjust brightness. So WLED backlight driver circuit can not simply On / Off design, you must also have a moderating drive current (thereby changing WLED brightness) the ability, and the increasing number of camera phones, digital cameras use flash WLED chance of getting type high, so the designers have to design two groups WLED driver circuit, a group for WLED backlight, a group for WLED flash, while two groups should have the ability to adjust the brightness.Graphic LCD Module
Since this type of design needs more and more, so many analog IC, power management IC industry have proposed solutions, namely WLED driver IC (English called: White LED Driver), driver IC can simultaneously control WLED backlight with WLED flash , including the On / Off light off control, brightness control, multi-stage, in which the brightness control as long as you can change the amount of current flowing through the WLED large flow is high brightness, flow rate is low brightness, change the way mineable voltage adjustment method or PWM (Pulse Wide Modulation; PWM) method.
The so-called voltage adjustment method is to change the WLED drive voltage, high voltage electric current flows through the WLED will increase, thereby brightening, or vice versa, then the voltage adjustment method to control the amount of current is not fine, slight change in voltage on the cause significant changes in the amount of current, unless you use very fine voltage adjustment circuit, but also make the cost and therefore the circuit complexity (volume) increased significantly. The PWM method is to change the relative WLED winking duty cycle (Duty Cycle), with WLED conduction (lighted driving) period percentage frequency to control the brightness, not only can fine adjust and the cost, complexity, are lower today WLED drivers IC widespread adoption of this method is to adjust the brightness.lcm module