The LED and switch combination has a 2 volt drop.
The battery is 3V. The current limit resistor has 1V at full charge.
When the battery drops to 2.5V the resistor has 0.5V. (1/2 current)
When the battery drops to 2.25V the resistor has 0.25V or 1/4 current.
I choose the resistor to give the desired current at 2.25 battery and 100% on switch.
Then at 3V battery I tell the IC to be at 25%. (4x current at 25% gives approximately the correct current)
We program the IC to give (in this case) 25% at 3V, 100% at 2.25V and below. The regulation is very crude. We do not drive the LEDs to full current, or ever near full current. QUOTE]
Hi ronsimpson.i am sorry
,but there one more thing that i try to understand.
you said
I choose the resistor to give the desired current at 2.25 battery and 100% on switch
if you choose the resistor to give the desired current,let say 1400Ma,at 2.25v battery and 100% on switch.it seems that when the battery is 3v the current seems to be 5600mA pulses(4*1400mA).
Then at 3V battery I tell the IC to be at 25%. (4x current at 25% gives approximately the correct current)
because at 3v the current will increase x4 to 5600mA ,and then 25% of this will give me the 1400mA current.and pulses of 5600mA is too much for the led.
i begin to get headache