In this post we study a LED driver circuit specially designed for backlighting LCD screens applications, Introductionlet' learn more about this interesting device.
Introduction
Today LCD products have become very common and a part of our everyday life. Whether it's your cell phone, DVD player, TV set, car, all incorporate LCD screens for indicating or displaying purposes.
The big reason of LCDs getting so popular is probably the presence of the back lighting that illuminates the entire surface of the unit brightly, making the relevant readings distinct and full of life.
LEDs are the prime components which are used for the above illumination applications. Genarally a group of high efficient LEDs are placed behind a responsive surface for getting the desired LCD effect or the back light illuminations.
For smaller color LCD units, around 8 white LEDs are usually sufficient for the required intensities. When placed uniformly, they almost present a perfectly balanced illumination of the LCD.
Circuit Operation
An effective LED driver circuit for LCD back lighting application has been discussed here which utilizes the IC ZXLD1100/1101/1937 from ZETEX.
The proposed circuit is based on the principle of PFM inductive boost converter concept.
The circuit is able to handle six series connected LEDs, powered by a Li-Ion cell and up to eight LEDs from a supply of 5 volts.
The ZETEX ICs are able to provide a good 350 mAof current for driving the above LEDs through a boost of up to 28 volts from the above discussed supply sources.
The minimum current required for keeping the IC operational is around 0.5uA, below which the IC shuts down itself.
The converter output is variable and can be varied by applying definite PWM control pulses across the enable pin out of the IC.
Depending upon the frequency of the fed PWM, the generated output is either chopped or a true continuous analogue.
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