On Mon, 18 Jan 2010 18:30:43 -0500, Hammy wrote:



Really how do you propose to alter the brightness with a constant
18mA?

If you say switch 18mA on/off at a varying duty cycle this will
change the average current and it will be below the peak current which
in this case is 18mA. This is dimming.

Example

25% duty the average current is ideally 4.5mA
50% ' '8mA
75% ' '13.5mA


If you maintain 18mA average current you can't change the brightness.
That is what you said is it not? Change the brightness without
changing the current?

The LED most certainly does see the average current that's how you
determine power dissipation in it unless you like to cook your LED's.

whoops the 8mA should be 9mA at 50% duty.