Re: current control algorithm



On 10/4/2011 6:33 AM, Jon Kirwan wrote:
On Tue, 04 Oct 2011 07:29:25 -0400, Walter Banks
<walter@xxxxxxxxxxxxx> wrote:

Tim Wescott wrote:

On Mon, 03 Oct 2011 13:58:06 -0700, cerr wrote:

Hi There,

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?

You just need integral control, which is dead easy.

If I tried to count the number of times I've wasted far more time on a
"time saving simplification" than I ended up spending finally doing a
control loop right, I'd run out of fingers and toes before I even
finished accounting for the first few years of my career.

--
www.wescottdesign.com

One of the first big engineering projects I worked on had a
blackboard that acquired anonymous one liners. One of these
gems has stuck with me for more than 30 years.

"If you have enough time to do it over how come you
didn't have a enough time to do it right?"

Cash flow.
Not every textbook solution is RIGHT.

.



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