Re: current control algorithm
 From: Arlet Ottens <usenet+5@xxxxxxxxxx>
 Date: Tue, 04 Oct 2011 14:16:09 +0200
I have two strings of 5 LEDs and a I need to control them with a pwm
to reach a certain intensity (I can measure the current). Now due to
lack of time , I didn't go with a PI controller (which I think would
be the right way) instead, I just calculate a hysteresis of x counts
(10bit adc) and the measured current has to be within this hysteresis.
Now I unfortunately got a high jitter on my LED current (that's
controlled by the duty cycle)  I assume this is because of a time
delay from the time i set the duty cycle until i measure the current
rise/fall. How do I best go about this?
Is there a quick method to resolve this or do i actually need to take
the time to study and implement a PI controller?
Every time you measure your current with the ADC, do something like this:
PWM += gain * (setpoint  current);
Calculations in floating point, or fixed point with sufficient bits, depending on your parameters, and clip PWM at min/max to avoid wrap around.
Experiment with different gain settings to see which one works best.
.
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