Re: Anotehr Basic Q. re: a circuit

Tim Wescott <tim@xxxxxxxxxxxxxxxx> wrote in
news:p6ydnRjHRZG1OgXVnZ2dnUVZ_sednZ2d@xxxxxxxxxxxx:

Kris Krieger wrote:
"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.

Yes this is the right group.

One of the basics of learning from newsgroups is that you'll get some
very negative emotions in your responses, sometimes.

If you get on to google groups and read a sampling of Phil's posts
you'll realize that this one is really quite positive.


I almost never Google past posts - I spend way too much time at the
computer as it is <LOL!> No, seriously, though, thanks for your note -
and yup, usenet is definitely a grab-bag, although I *have* gotten some
really good answers over the past several weeks from several people,
which *has* helped me understand a lot more than I had, and also has
given me much better search terms to use :) - OTOH I was honestly
serious as to asking whether this is the right group for the question I
was asking. I've tried to be up-front re: the depth and extent of my
lack of knowledge, and the fact that I'm trying to teach myself, but
maybe that didn't come through - if there is a better venue, I'd
appreciate knowing that.

I've seent hat "circle" a fe wtimes on circuit drawings, tho', and I
havent' seen it explained in the resurces I have currently, so it always
confuses me, since it looks to me like it means "add more stuff here".

Well, my books should get here is a few days (delivery was probably set
back a bit by Eduardo, alhtough he seems to have shed his wolf-skin, at
least in my area, mainly delivering a steady, soaking rain with only
brief torrents). Hopefully, the new texts will give me a good dose of
enlightenment ;)


- Kris






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