general question about LED drivers

[zmogedra]

So I’m now very familiar with led drivers. I know they act as current sources, but from there the effectiveness comes from? Is this because they give as much voltage as LED needs with a fixed current, depending on LED’s internal resistance? I have 4 3W led’s bought from Hon Kong the only spec. they had is: If=750mA, Voltage min3V, max3.2V. I will be running them with 12AA rechargeable batteries 3000mAh. I was thinking to run them separately 3x1.2V. Would I benefit from a LED driver, because I only need to drop voltage by 0.4volts? If so is there any cheap DIY one?

[znomit]

So I’m now very familiar with led drivers. I know they act as current sources, but from there the effectiveness comes from? Is this because they give as much voltage as LED needs with a fixed current, depending on LED’s internal resistance? I have 4 3W led’s bought from Hon Kong the only spec. they had is: If=750mA, Voltage min3V, max3.2V. I will be running them with 12AA rechargeable batteries 3000mAh. I was thinking to run them separately 3x1.2V. Would I benefit from a LED driver, because I only need to drop voltage by 0.4volts? If so is there any cheap DIY one?

Yes you need a driver of some sort because battery voltage is not constant. For a NiMH it varies from 1.0 to 1.4V.
You can use a resistor to drop the voltage but efficiency is not so good.

[zmogedra]

Ok, now I know that I need a led driver and Nimh batteries for every 0.1C discharge voltage drops by ~1.25V. Maybe you know a DIY driver? I think it could also include a PWM mode to save some of that juice.

[znomit]

Ok, now I know that I need a led driver and Nimh batteries for every 0.1C discharge voltage drops by ~1.25V. Maybe you know a DIY driver? I think it could also include a PWM mode to save some of that juice.

For cheap LM317 is ok and easy to find. I use this for bench testing.
It needs a 3V overhead which might be ok depending on your LEDs(at 1A Vf varies from 3.25 to 3.7 for different LEDs).
http://users.telenet.be/davshomepage/current-source.htm

Heres an intro to drivers and theres a list at the bottom
http://www.videofoundry.co.nz/ianman...vers_why.shtml

Check out dealextreme for low cost drivers.
Check out taskled for high quality.