[HELP]Second red build! Attempting to use own driver.

[Ethereal]

The chip I'm going to use is LTC3490 Linear Technology - Product Page
It features quite minimal components, and runs from a single Alkaline / Nimh cell. Goes up to 4v/350ma
I think this is pretty good for a ML101U29 which is a LOC
And the fact that it's a continuous negative driver appeals me.
This is also my first time making a PCB board and also mounting SMDs. Quite a jump from through holes I think. Not gonna reflow, just soldering with iron.


I have a few questions though, if anyone is willing to help?
1. The chip features a low battery indicator pin, but I'm not exactly sure how it works, does it: send an output? turns off something by some sort of potential divider? I can't really tell from the circuit.
2. Though it's unlikely someone will open up the flashlight and reverse the battery, I want to stay safe.. where should I put a diode to implement reverse voltage protection?
3. The soft turn off sounds pretty cool, what about soft turn on? Is there a way to make it happen?
4. What is "dimming"? is it literally dimming like reduced current? doesn't seem like it
Lastly, it says 4v, so the LD will just take what it needs (3.x)V?

I've also heard of the driver 'casing' being referred as a "pill" . Is it important or just something to keep it tidy? I think I already have an answer while I write this

Thanks people

P.s should I tag my threads?

 

[jimdt7]

If you are looking for 350mA output why don't you use the AMC7135? :thinking:

Jim

 

[rhd]

If you are looking for 350mA output why don't you use the AMC7135? :thinking:

Jim

I have to agree.

While I applaud your interest in going with a DIY boost driver (the forum needs more people like you!), that seems an overly ambitious approach given the task.

Any host that can use a single alkaline, can probably use a lithium ion equivalent. For:
C -> use a "26650" lithium ion
D -> use a "32650" lithium ion
AA -> use a "14500" lithium ion
AAA -> use a "10440" lithium ion

If you use a single lithium cell, then you're over the Vf of your diode, and you don't need to do any boosting. The AMC7135 IC costs under 50 cents, and basically needs no external components except for a couple small caps.

You're also welcome to use, or adapt however you see fit, my AMC7135 schematic and board here:
http://laserpointerforums.com/f67/open-source-iron4d-driver-single-cell-diode-mits-driver-87677.html

 

[Ethereal]

Was actually looking for output around 350-450ma
The chip seems pretty neat, no components, but I'll have to insulate the heatsink / module.
The amc chip didn't appear in my local element14, so I would have to go for eBay :-[ yeah it's very cheap
that is, if I choose this one
is there any other good DIY drivers in this range of current?
preferably continuous negative.
most drivers I've seen has a low reference voltage of around 200mv, which is kinda troublesome to get really low resistors.
Just got a "5mw" 405 eBay pen today
Apparently the tongue and eyebrows are good at absorbing heat hahaha. blu ray is so beautiful, when it fluorescent it can light up the whole room.

 

[jimdt7]

Apparently the tongue and eyebrows are good at absorbing heat hahaha. blu ray is so beautiful, when it fluorescent it can light up the whole room.

I hope you didn't try that...

There are also binned AMC chips which output 380mA, check out www.fasttech.com

Jim


Sent from my HTC One using Tapatalk

 

[BShanahan14rulz]

If you use a single lithium cell, then you're over the Vf of your diode, and you don't need to do any boosting. The AMC7135 IC costs under 50 cents, and basically needs no external components except for a couple small caps.

You're also welcome to use, or adapt however you see fit, my AMC7135 schematic and board here:
http://laserpointerforums.com/f67/open-source-iron4d-driver-single-cell-diode-mits-driver-87677.html

The caps are usually only necessary if you have a distance of more than several cm between the chip and the load.

Also, RHD forgot to mention his MAGIC, which you would be interested in, AND which would easily run on the extra voltage available from using a lithium ion cell. If you haven't read, the MAGIC is a set of specially chosen FETs, which introduce a very small voltage drop in the circuit. Since you are driving a red off of a Li-Ion, you have plenty of voltage overhead.
Now, what it does for you? It allows you to put the battery in backwards or forwards, doesn't matter, either way, your laser will work!

 

[Ethereal]

Can't really find any simpler ICs than the one mentioned
I'll probably go with 380ma and try to squeeze a 18650 in the AA host. It's just 4mm thicker, it should fit according to the picture.
Everything is being shipped, so I wouldn't know :s
As for the circuitry, it's a bit different from the datasheet, the caps placement are different. Don't really get the function of the capacitor near the ground. Not like I'm an electronic expert to judge.
I think I should take some time off laser building for now. Trial exams in a month's time D:
All these planning is always exciting yet takes a lot of time.
Thanks for the response guys!

 

[jimdt7]

Good luck with your exams! :beer:

Jim

Sent from my HTC One using Tapatalk

 

[The Lightning Stalker]

Doing the reverse protection depends on the chip. Some chips will act like a diode all by themselves
requiring no external circuitry. It's hard to tell until you actually have a chip in hand to test. What I
would do is use a constant current source, such as a liner laser diode driver for instance, to limit current
and hook up the chip backwards and see what happens. If there is any flow, you need some kind of
external reverse protection. You will need more than just a diode in a battery powered circuit though
because of voltage drop. A friend of mine put together a little reverse protection circuit that uses a
MOSFET and a couple resistors. There is no voltage drop in a MOSFET, so it is the perfect solution. If
there is enough voltage there, you might be able to get away a Schottky diode. but it will still drop about
0.2V.

To answer your other question about the low battery pin, it is active low. See that little bar above the
LOBAT? That means it is an inverted pin, or NOT. So it will pull to ground when the batter is low.