'Floating' AMC7135 Driver for More Volts?

[Spectre Gadget]

Hello fellow photon junkies...

I've had a few projects that have yielded some spare 1W LEDs that I would like to repurpose as computer case lighting. I also have some bulk-bought AMC7135-based drivers at my disposal.

I am wondering, has anyone here ever tried to use a voltage divider to float one of these drivers so the circuit load (laser or LED) can run on a higher voltage than the regulator? See image below:



A few things to note:

• The 12VDC power is supplied by the PC's power supply. Plenty of overhead and clean power. Plus, battery life and circuit efficiency aren't as important here.
• I've measured the driver input and output leads and the positive (+) side is common throughout the circuit. Therefore I'm thinking it's controlled from the negative side.
• Size constraints not important. Big resistors will fit inside a computer case no problem.
• Output LEDs will be in two parallel banks with ballast resistors, to drop the current by half. I like running my LEDs at half max to reduce heat load and increase longevity.

Any thoughts would be great. If I'm crazy, let me know and I'll check myself into a rubber room. If not then I'll probably go resistor buying and get this thing working. I've recently finished a project where I used 1W LEDs for more of a functional purpose and it made me want to apply it in a more aesthetic approach.

Thanks folks!

UPDATE 17 June 2013...

This past Friday I slapped the circuit together to see if the LEDs would drive. The verdict is NO. I could measure the voltage drops across the LEDs, but the current simply would not flow. Oh well, at least we all know.

 

[BShanahan14rulz]

Poorman Mutli-Lux setup method

This is basically what you are after? Running more LEDs from higher voltage source than the 6V max? Since it is linear driver, can just use the input voltage (instead of non-light-emitting-resistors), and use LEDs to drop voltage until low enough for to not fry the 7135 chips. As long as you are burning energy, might as well make some light too.

 

[Spectre Gadget]

WOW... that's great! I didn't think about using the LEDs instead of the voltage divider. Thanks for that!

I think I would still need ballast resistors to set parallel banks of LEDs 'on even keel', but then the O/P would only be about 5.1-5.5 VDC. That would be a little much to drive 1 LED, but not enough for 2.

For illustration (quick and dirty):

12V---2S 2P LEDs ------5.6V--- (DRIVER, -.1V) ---5.5V



GND-------------------------- (DRIVER, return) ----?



I hope that's not confusing. Oh, and the specs for the LEDs are 3.2-3.4VDC, 350mA max.

 

[BShanahan14rulz]

I've historically forgotten some random details that turn out to be pretty important, but yeah, I think you got it right.

The 5.5V left over after the driver is enough for one LED, the left over voltage will be dropped in the regulator as heat.

 

[Spectre Gadget]

It definitely seems simple enough. I'll play with some numbers when I get a moment and decide whether dissipating that extra 2VDC or so is more efficient than dissipating it through a voltage divider.

We're still open to comments, especially if there's experience behind it. Anyone feel free to post any opinions on the subject. Thanks for your help BShanahan!