Boost Converter for White LEDs

[Willt]

Hi friends,

I'm going to do my FYP in the coming academic year on boost converter (IC design) for white LEDs connected at the output in series. The converter should be able to drive different number of LEDs whose brightness could be controlled.

I would be very appreciated if you could leave a few words for the following questions:

1. I know white LEDs are for backlighting of portable electronic devices or torch. Why are white LEDs so popular? Why not red LEDs? Or blue LEDs?? Do white LEDs consume more power than other LEDs? The brightest?? Any recommended website or document for white LEDs?? Thanks ~

2. Are there any commercial products that could be good references (or you have the experience of using it) for such project?? Any design notes recommened??

Thanks for your help in advance. Your comment would be very appreciated ~

Will

 

[junior05]

Which structures do you want to design?
charge pump or PWM DC-DC converters?

 

[Willt]

PWM or PFM or VFM dc-dc (boost) converter
I need to compare different configurations or topologies or control mode (voltage or current mode control), and make decision.

Thanks for your comment ~

 

[vicky]

HI DEAR I THINK IT WOULD HELP YOU.


In 1992, bright blue LEDs made from GaN were invented by Shuji Nakamura in Japan. White LEDs were then made based on the technology used in blue LEDs.

LEDs have a high light to power effiency, up to 40LM/W. They are much more durable than conventional lightbulbs. The expected lifetime for LEDs is up to 100,000 hours. These advantages have made the LED flashlight popular.

The voltage to drive a LED is 3.0V to 3.6V. So a step up circuit should be used in LED flashlight using 1 or 2 1.5V dry battery.


Blue and white LEDs

An ultraviolet GaN LED.Commercially viable blue LEDs based on the wide band gap semiconductor gallium nitride and indium gallium nitride were invented by Shuji Nakamura while working in Japan at Nichia Corporation in 1993 and became widely available in the late 1990s. They can be added to existing red and green LEDs to produce white light, though white LEDs today rarely use this principle.

Most "white" LEDs in production today use a 450 nm – 470 nm blue GaN (gallium nitride) LED covered by a yellowish phosphor coating usually made of cerium-doped yttrium aluminum garnet (Ce3+:YAG) crystals which have been powdered and bound in a type of viscous adhesive. The LED chip emits blue light, part of which is efficiently converted to a broad spectrum centered at about 580 nm (yellow) by the Ce3+:YAG. The single crystal form of Ce3+:YAG is actually considered a scintillator rather than a phosphor. Since yellow light stimulates the red and green receptors of the eye, the resulting mix of blue and yellow light gives the appearance of white, the resulting shade often called "lunar white". This approach was developed by Nichia and was used by them from 1996 for manufacturing of white LEDs.

The pale yellow emission of the Ce3+:YAG can be tuned by substituting the cerium with other rare earth elements such as terbium and gadolinium and can even be further adjusted by substituting some or all of the aluminum in the YAG with gallium. Due to the spectral characteristics of the diode, the red and green colors of objects in its blue yellow light are not as vivid as in broad-spectrum light. Manufacturing variations make the LEDs produce light with different color temperatures, from warm yellowish to cold bluish; the LEDs have to be sorted during manufacture by their actual characteristics.

White LEDs can also be made by coating near ultraviolet (NUV) emitting LEDs with a mixture of high efficiency europium based red and blue emitting phosphors plus green emitting copper and aluminum doped zinc sulfide (ZnS:Cu,Al). This is a method analogous to the way fluorescent lamps work. However the ultraviolet light causes photodegradation to the epoxy resin and many other materials used in LED packaging, causing manufacturing challenges and shorter lifetimes. This method is less efficient than the blue LED with YAG:Ce phosphor, as the Stokes shift is larger and more energy is therefore converted to heat, but yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both approaches offer comparable brightness.

The newest method used to produce white light LEDs uses no phosphors at all and is based on homoepitaxially grown zinc selenide (ZnSe) on a ZnSe substrate which simultaneously emits blue light from its active region and yellow light from the substrate.

A new technique just developed by Michael Bowers, a graduate student at Vanderbilt University in Nashville, involves coating a blue LED with quantum dots that glow white in response to the blue light from the LED. This technique produces a warm, yellowish-white light similar to that produced by incandescent bulbs.

 

[rajblr]

hi sir, even i am working on such project for the first time. I am basically a DAC guy, doing DC-DC boost converter for the first time. So ca you or some one provide some material or information on artitechtures, control method and block level information of DC-DC converter for white LED driving.


TIA
raags

 

[gevy]

Look attached paper

 

[colinwang]

You may take FAN5608 as a reference.