Upcoming chip from Linear

[Entropy]

While it isn't completely optimal for LED driving (As it's a constant voltage, not constant-current circuit, although with a small opamp it could be made more suitable for CC applications), Linear is releasing a controller chip that could be a dream for 5W modders. The part number is LTC3425 - It's essentially 4 parallel step-up controllers in one, and is capable of quite a bit of output current. With such a regulator and an external op-amp for current sensing, 5W in a 2-cell config (2AA not likely, 2D very likely) should be possible. While it would be a miracle to get it to fit into a AA "pill" (Although dat2zip never ceases to amaze me... /ubbthreads/images/graemlins/smile.gif ), it would probably be easy to fit one or possibly even two of these with an op-amp for current sensing onto a "ring" board that went around the bulb holder post in a 2D or maybe even 2C Maglite.

 

[dat2zip]

Entropy,

The Part number immediately caught my attention and I took a quick peek to confirm my suspicions.

This is an LTC (where the C designates a CMOS Process).

Linear and Maxim CMOS process is highly tuned and optimized for 5V and lower operating voltage and are typically rated for MAX V of 6V.

This part is similar to those and Vout is only good to 5.5V or so my 2 second glance at the data sheet showed.

BTW: Almost any regular voltage converter with the appropriate Opamp can be made into a CC driver.

Wayne

 

[Entropy]

[ QUOTE ]
dat2zip said:
Entropy,

The Part number immediately caught my attention and I took a quick peek to confirm my suspicions.

This is an LTC (where the C designates a CMOS Process).

Linear and Maxim CMOS process is highly tuned and optimized for 5V and lower operating voltage and are typically rated for MAX V of 6V.

This part is similar to those and Vout is only good to 5.5V or so my 2 second glance at the data sheet showed.

BTW: Almost any regular voltage converter with the appropriate Opamp can be made into a CC driver.

Wayne

[/ QUOTE ]
Argh. Need to avoid posting any time before noon. (Not that I'm much more alert right now). Missed the 5.5v limit on the output.

Might be useful for a parallel 1W or parallel 3W config.

If only something like this were available with a higher output voltage...

The 1618 still seems to be king. I wonder how difficult it would be to hack it to control an external transistor to allow for higher current operation.

 

[dat2zip]

There are many good possible combinations that would be high efficient and compact that are currently do-able.

For the 14.5mm or AA battery diameter, there is very little real estate to work with. Given the diameter of the mag head and or heatsink area there are IC's from almost any MFG that will do the job and then some.

Like I mentioned before, a two IC setup can be done with National, Maxim and LT (plus others).

I just haven't gotten around to expand beyond the 2AA domain.

For highest efficiency, you'd probably want a small IC and drive an external FET of some form. That would then be IC, FET, Opamp as the primary parts.

Another possible combination is to use an IC with more pins and use two external FETs and do a syncronous version. With a combo like that, you should be able to one that will hold 92-95% efficiency especially for the 5W design.

As your output power goes down the harder it is to keep efficient since a mA here or there could be a significant loss in terms of efficiency. The converter draws power, the Opamp draws power and these rob from the efficiency numbers.

Wayne

 

[Entropy]

Yup. I've found quite a few candidates from National Semi (One of my favorite manufacturers, due to ease of obtaining their products, including samples.) It's just a matter of the time and money to actually put a circuit together. /ubbthreads/images/graemlins/smile.gif

One of EL's heatsinks could easily be modded to heatsink a switching transistor in addition to the Luxeon.