Comments on: 3 Channel Driver

By: John

John — Mon, 15 May 2006 04:43:03 +0000

And on the calculations with LM1085, you say that the regulator would use 2.59 watts and the resistor would take 0.98 watts.

So am I right to say: Total wattage including everything would be…

2.59watts + 0.98watts + (4* 3W) = 15.57W?

Where the (4* 3W) is the wattage of the four LEDs…

Have I done some stupid calculations like before again?

By: John

John — Sun, 14 May 2006 22:50:05 +0000

Oh… forgot to ask, how do you work out the capacitor values for the current regulator? And is it required for my application when I only need instant mono colour light from the LEDs when I step on the brake?

By: John

John — Sun, 14 May 2006 22:41:57 +0000

Thanks so much for the detailed reply JustDIY!

I am getting the cheaper ProLight Luxeons, so driving at 700mA is what they recommend…. 1400mA would probably burn those LEDs badly! :P

And I will certainly go for the LM1085 option. But is the adjusting resistor’s value calculated the same way with it? And is a huge heatsink required on the LM1085 itself?

And what happens if the voltage of the car falls to about 10V (which could happen sometimes in my old car, especially during start up), will the LEDs fail to light at all?

I will mount these 4 LEDs on an old Pentium II processor forced air heatsink, which measures 5cm x 11cm x1.5cm, do you think it will be enough to keep the LEDs cool?

Actually, how hot does these LEDs actually gets when running? I have never bought them before, so I am just putting a bet on making something that would work….

Thanks so much for helping!