Re: Am I right?

On 15 Feb 2007 16:26:28 -0800, "Richard Henry"
<pomerado@xxxxxxxxxxx> wrote:

On Feb 15, 9:20 am, "Dave Pollum" <vze24...@xxxxxxxxxxx> wrote:
On Feb 15, 11:02 am, Don Lancaster <d...@xxxxxxxxxx> wrote:





Michael wrote:
I have some 1 watt LED's that I want to flash on and off.

I have a 317 current regulator supply set at 300 ma for 3 of them in series.

Now, I know there are alot of professional designers on this group and was
wondering if I couldn't get an opinion on my approach to this, as it makes
sense to me.

I know many decisions are made based on parts cost but either way I do this,
the cost is about the same....the cost aspect is not what I'm concerned
with.....just if I'm making "the right choice".

I initially thought I'd use a 555 timer to have a constant flash rate on an
optoisoltor LED and control on/off with the LED ground.....then use the opto
output and a sink transistor to control the DC path.

Cons: what if anything were to change with the transistor and present a
change in the DC series circuit?....could I get an "on resistance" that
would be low enough and STAY in a specific window? With 300 ma flowing
through, some "potential" for disaster would be there.

So....

Why not this....which makes more sense to me....

Control the AC to the transformer with the same setup....flash a triac
driver opto LED with a 555, control on/off with the opto LED ground, use a
triac to switch on and off the transformer primary?

That's what I have breadboarded now...works fine.

Don't you think it would be the proper way to go as far as a design
decision?......it lets the cc power supply be stable and avoids risk?

The only risk on doing it the AC way is an AC line surge but I'll use a
400 - 600v triac good for 1 amp or so.

Thanks.

Use a PIC.

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss:http://www.tinaja.com/whtnu.xml email: d...@xxxxxxxxxx

Please visit my GURU's LAIR web site athttp://www.tinaja.com

Don,
It seems like the cure for everything except the common cold is either
a 555 timer or a PIC ;)

The cure for a 555 timer is a PIC.

Programmed to look like a 555?

OK, that works for me. ;)


--
JF
.

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