Re: Anotehr Basic Q. re: a circuit

"Phil Allison" <philallison@xxxxxxxxxx> wrote in
news:6fnev2Fcg4atU1@xxxxxxxxxxxxxxxxxx:


"Kris Krieger"
"Phil Allison"


Sorry for another stupid question, but, I'm looking at this
http://www.maxim-ic.com/appnotes.cfm/an_pk/1750
and can't figure out whether I can ignore, or whether I need to add
in some
modification of something like this
http://www.instructables.com/id/S8Q5N9QFHTAIQK7/
where the first diagram says
" PWM Dimming 0 to 3.3HZ f>15KHz 0%=shdn 100%=20mA "

A clue would be appreciated - especially since I don't know whetehr
they mean dimming as in a Dimmer Switch on a lamp, or whether they
mean something entirely different...


** The CTRL input operates to dim the LEDs with a 0 to 3.3 volts
variable DC input, which can be created by filtering a PWM signal
as shown or any other way you like - eg with a 3.3 volt supply and
a pot.


In the Data*** for the IC, in the chart describing the Pins, for
CTRL, it
says:
"Brightness/Shutdown dualmode control input. LED brightness and IC
shutdown are controlled by the voltage on CTRL. VOltage between
250mV and 5.5V or (V+ + 2V), whichever is less, adjust the brightness
from dim to bright, respectively. To put the IC into shutdown, drive
below 100mV or connect to GRND."

So, for a low-voltage light (2 or three 1.2V NiMH batteries, 1500mA
to 2500mA), that means it's jsut personal choice rather than
mandatory to add in the dimmer?, IOW, I can either add in a dimmer,
or just connect the pin to the ground/out terminal?


** Why are YOU crapping on about adding a " dimmer " all the time ??

That IC has a built in dimming function which operates as stated.


Because I'm teaching myself, and I didn't understand that - the diagram
showed it connecting to something, and I didn't understand what that
"something" is. To me, it looked like some separate IC or circuit
becasue, if it was suposed to just be connected to teh ground, I assume
it would have shown the symbol for that, rather than a circle. Now, if
sci.electronics.basics is not the place to ask basic questions, please
let me know what would be a more appropriate venue for people who are
trying to learn on their own and have similarly-basic questions, and I'll
be glad go to that NG (or forum) instead.






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