Need Help Mod wiring - A few question on steping down voltage with resistor

[Java_Az]

The LM317 has a pretty big drop out. 1.2 volts compared to .3 of a volt for the Ti chip. Although it wouldn't make much of a difference for a set regulation of 4.2 volts it would on a 5 volt or adjustable mod. Plus a 3 amp rating just just looks better on the drawing board then a 1.5 amp

 

[McDude]

Of course one advantage of the TI chips is the control pin. I noticed int he LM317 datasheet that they believe 1.2v is enough of a "shutdown" and it may be, but I want 0v going to a heating coil while the device is in my pocket, so there's no efficient way of having a low-amp momentary on the device. I myself don't like just cutting power/restoring power as a means of turning a device on and off, it seems kinda "harsh" on the chip (just my own feeling on it lol). Hmm, maybe there would be a way of using a mosfet with a higher than 1.2v thresshold to cutoff current to the coil if the adj pin is taken to ground, not sure.

 

[Rockproof]

Ok, just got back into this post. Agreed I need "helping hands" device. Got that one...the rest hmmmm...nope. Has there been an agreement on what would be the best way to drop to 4.2? If so, what? Where can I get one and how would I wire this into a copper mod?

Thanks again all for the feedback. Keep it coming, I'm learning.

 

[Java_Az]

For either regulator they are the same as far as getting it to 4.2 volts. you need two resistors 240 ohm for R1 and 560ohm for R2 That will give you 4.219 volts. Look at the data sheet for typical diagram on how to wire it up.

 

[AttyPops]

mcdude, Java, yeah all good points. I only asked (hence the "Question:") since the OP was looking for a nice easy solution. I use the 5v 4 pin regulators myself, but I have a 317 in the parts bin and it made me think/ask. I suppose you could add a power mosfet to do the switching with a low-amp button, but that defeats the whole purpose of keeping it simple (starts getting a little Rube-Goldburg-ish lol).

The part I have is an LM317T rated at 15 watts. C out is limited to 1.6 amps tho.
If he's using, say, a 2.5 ohm atty at 4.2v he only needs 1.7 amps. Since it's intermittent, that's pretty close. Heat sink???
However, his desired 1.5 ohm atty requires 2.8 amps. He'd be better upping the voltage then. (More on the atty below)

I'll bet that the power cycling it is a bit hard on the chip; a cap on the input may buffer that a bit, IDK. Just thoughts. I'm interested to see how this comes out too.

BTW Rockproof, I'm not saying you SHOULD use this, just asking how it would work to keep things simple. You sure you want a 1.5 LR atty at 4.2??? That's 11 watts......

P.S. The UCC383 looks like a much better chip for this application.......

Also, whatever you do, think about vent holes .... and protected batteries..... and e-cigs + water don't mix.... nice fish.