Variable resistor with micropuck?

[pedalinbob]

i am going to build a 3-6 led pocket light. i can use 3aaa and still meet my size requirements.

however, i could use 2aaa (even smaller overall size) or 2aa (greater capacity and still pretty small)...with a micropuck. but, i think the MP puts out 350ma, which would be too much for the poor little nichias (i still may reconsider, and use a nice LS1w that i have. if i use the luxeon, i will still use the variable resistor).

so i think i may try this: 2aa with micropuck, resistor, and variable resistor. the first resistor would prevent overdriving the led's too much when the variable resistor is set to it's lowest resistance (0.7 ohm).
the variable resistor would be used for dimming.

would this setup work, or will the electronics be goofed by the resistor(s)?

just an FYI: i will be building this to be either 2.4"x1.4"x0.8" or 3.15x1.57x0.8, and will have a thumb wheel variable resistor with built-in switch, which will protrude slightly from the top-forward portion of the case.
(i would love to use a flush-mount switch with electronics from a palight onestar...but have no idea how to do it or even if it would work!)

i will try to keep the outline as smooth as possible for pocketability and to prevent accidental activation.

i will probably create a raised lip to protect the switch/dimmer, and either recess the led's or attach a small guard around them for protection, and to prevent back-spill.

thanks!

Bob

ps i already e-mailed the micropuck folks, but havent recieved a response...

 

[tvodrd]

pedalinbob,

The MicroPucks I am playing with do not appear to be constant current drivers like WayneY's badboys. As Vin decreases, Iout decreases. Try paralleling some 5mm whites with 1.5 or 3V in. I think somebody here has already done it with decent results.

Larry

 

[Bandgap]

If you can find a suitable variable resistor, that is a simple way to make a dimmable circuit. Unfortunatly, low value variables with suitable current capability are rare.

If you cannot, there are several ways to make a simple linear regulator.
How interested in efficiency are you.
If you can build electronic circuits, a pretty efficient and dimmable linear converter can be made using a National Semiconductor LM10 and a good transistor (I know, I have said this before /ubbthreads/images/graemlins/smile.gif) - providing you are running the whole thing from three NiMH cells.
Steve

 

[Hemingray]

1AA or AAA with a micropuck will do nicely with 6 to 8 white
LEDs, 16-18 with 2 AAs.

One thing I noticed, as I was trying out a micropuck with no output load, is that the unloaded output voltage, using 3VDC,
is about 28 VDC.

I'm not familiar enough with the 'puck's ratings, perhaps a series-parallel LED array would also work?

/ed B in NH

 

[pedalinbob]

um, well. i have never tried doing any real electronic work. just simple lighting circuits.

i intend to use alkalines...would this circuit work?

would the linear regulator work in conjunction with a button or dial?

where can i find info on making this circuit?

thanks, Bandgap!

Bob

ps my rationale for building this light is pure utility. i regularly use a palight on low setting for reading at night. i also use an attitude or LS based minimag for other household/outside chores. i want a light to do all of these things, AND be pocketable.

the biggest trick now is finding a way of dimming/switching. actually, i am experimenting with some variable resistors with different values: i may not even need an on-off switch. by cranking the resistor up, i can dim the led similar to the palight "always on" mode.

 

[Bandgap]

I have got to dig my circuit up at home.

Have you thought about just having a two or three position slide switch with a handful of fixed resistors?
That would be easy.

To be going on with, here is one circuit which looks like it should work with a few mods.
http://radiolocation.tripod.com/LEDdimmer/LEDlampDimmer.html

I can remember, but cannot find, a reference to two circuits made in the forum a couple of days ago. There were pretty neat circuits.
Take a look over the last couple of dozen postings on this part of the forum.

Hopefully, I will remember to bring the circuit in tomorrow.

Steve

 

[pedalinbob]

yup--i still may use a multiswitch with resistors--might be a very simple solution.

many thanks for all your help--this will help me to decide what to ultimately use.

Bob

 

[Bandgap]

I have a circuit.
It may be a litle over-designed, but it works wekk.

I willhave to fax it.
Do you have a number pedalinbob?

If not, I may be able to scan it.

Steve

 

[pedalinbob]

yes, i have a fax, but it is not always on...

scanning would be great!

again--MANY thanks for your help.

Bob