small lm317 driver advice needed

kiyoukan · Oct 2, 2010

Hello, i have been building lm317 with normal threw hole components but in recent times i want to covert to smd ones.
Here are a list of parts i wanted to use and know if they will work.
All part numbers from digi key

Resistors:
P1.0ECT-ND 1.0 ohm
541-1.3ECT-ND 1.3 ohm
541-2.0ECT-ND 2.0 ohm
P2.4ECT-ND 2.4 ohm
(all are 1/4 can 1/8 be used?)

Capacitors.
PCE3169CT-ND
(Whats the smallest uf cap that can be used?)

Diode
S1ABDICT-ND
(Currently out of stock. can any diode be used?)

LM317TFS-ND
The whole point to these parts is to be able to build the driver small enough to fit into an axis housing.
I am able to get it to fit with regular threw hole but it take a ton of work.
I want to be able to use smd so i can save space while still getting the current and power i need.
Thanks for any advice or sugestions.

Eudaimonium · Oct 2, 2010

You can throw out the capacitor and the diode for smaller driver.

You can also use LM1117, lower Vdrop, it'll make battery cycle longer in some cases.

Resistors ... preferably greater power.
Here's a really old picture of a driver I made long ago:

There is capacitor bleeder resistor, parralel to the diode. You can omit both the resistor and capacitor.

Notice how through (!) hole resistor is mounted.

kiyoukan · Oct 2, 2010

Well i like the LM1117 for a low powered build but i still ned the 317 for my high powered ones.
But you dont need a capacitor? and or a diode?
Then what protects it from reverse current? or is that just the penalty for small space?

Rafa · Oct 3, 2010

kiyoukan said:
Well i like the LM1117 for a low powered build but i still ned the 317 for my high powered ones. <-- This makes no sense at all. LM1117 and LM317 are capable of givin up to 1A so... LM1117 only drops 1V and gets less hot. If you want a radiator go for the LM317.

But you done need a capacitor? and or a diode? what?

Then what protects it from reverse current? or is that just the penalty for small space? <-- The diode is not a must. You can either use it or not.

I edited your post.

kiyoukan · Oct 3, 2010

as far as digi key goes the only LM1117 they have are 800ma.
And thats great for a small build of low power but when i want a 1.4a build i need the 317 but i just wanted to know if those smd components will handle everything.

Eudaimonium · Oct 3, 2010

You can use two driver boards in parralel. Also, for 500mA and above, heatsink is needed on LM chip (317 needs bigger heatsink you know).

For 1.4 A, portable build is next to impossible with linear driver. I can only think of 1 W IR or 1W 445nm.

In either way, you're going to need to heatsink the driver. That being said, what's the point of small SMD driver if it's gonna keep a small room warm anyway?

kiyoukan · Oct 3, 2010

well i have a design to keep in my new hosts that allows for a huge heat sink 1 5/8 wide by almost 2 1/4 in deep.
I have gotten great results with the 317s and just want to make them smaller. i heat sink the 317s by
making them fit into the 12mm hole but on the back side of the 317 i have a half moon shaped piece on the back and in between them is a thermal isolation pad.
So the driver along with the laser gets pressed into this large heatsink.
but i need to be able to build it with small components.
So am i right in thinking that all of those will still be good to use and get me the protection i need?
This way i can make the heat sink removable and have the driver come with it.
Allowing me to switch it out for different colored lasers.
I just dont want to go and buy 50 smd components only to find out they are too weak to handle the power.
Also a note i can get any driver chip such as the 317 or any other as long as they are made by stmicro for free so i dont care what chip i use or form factor as long as it can work.
Are there any other linear driver chips with similar power but less v drop than the 317?

Eudaimonium · Oct 3, 2010

kiyoukan said:
well i have a design to keep in my new hosts that allows for a huge heat sink 1 5/8 wide by almost 2 1/4 in deep.
I have gotten great results with the 317s and just want to make them smaller. i heat sink the 317s by
making them fit into the 12mm hole but on the back side of the 317 i have a half moon shaped piece on the back and in between them is a thermal isolation pad.
So the driver along with the laser gets pressed into this large heatsink.
but i need to be able to build it with small components.
So am i right in thinking that all of those will still be good to use and get me the protection i need?
This way i can make the heat sink removable and have the driver come with it.
Allowing me to switch it out for different colored lasers.
I just dont want to go and buy 50 smd components only to find out they are too weak to handle the power.
Also a note i can get any driver chip such as the 317 or any other as long as they are made by stmicro for free so i dont care what chip i use or form factor as long as it can work.
Are there any other linear driver chips with similar power but less v drop than the 317?

That's what we're telling you, 1117 has aproximately half Vdrop than 317.

SOT SMD case will only give you 0.8 A , yes. Having two in parralel i solution. Make singlesided board with two ICs one next to eachother so they are both cooled by heatsink you described.

kiyoukan · Oct 3, 2010

hmm using 2 lm117 wont using 2 give me the same vdrop?
if not i might just go that route.
So lets say thats the way i want to go.
Do i need 2 resistors for each or can they just be stacked with the same components?
Sorry for some of these seemingly bad questions as i am still learning and this will be my first time 2x a driver.

Vaporizer · Oct 3, 2010

Not if they are in parallel. If you have a dual sided PCB with 1 LM1117 on each side, you have the room for a second resistor. Actually even if they are on the same side sharing a common heatsink.
If you are concerned abt the resistors wattage, measure the ma between the LM1117 and the resistor. It's a 1.25v Vref so know the ma's should easily give you the resistor wattage needed.

Rafa · Oct 4, 2010

Well.... Linear drivers for portable builds just suck. Why don't you get a serious Switching driver?

Eudaimonium · Oct 4, 2010

Rafa said:
Well.... Linear drivers for portable builds just suck. Why don't you get a serious Switching driver?

Price, dude.
You can get 25 pieces of LM1117 SMD ICs for $10 shipped on eGay... uhh I mean eBay.

Some people like to build stuff instead of buying it. [Nothing particular towards you, I'm just saying]

Rafa · Oct 4, 2010

I like to build rather than buying.

He can also build a Switching driver of course.

Vaporizer · Oct 4, 2010

Price and just building it yourself can be major factors.
You can use 4 7135's in parallel in the SOT-89 pkg with a common heatsink. It also comes in a TO-252 pkg too.
http://www.micro-bridge.com/data/ADD/AMC7135.pdf
No problem getting to 1.4A with these. Support parts can be common and are minimal.
DX has all kind of deals on these.

Another option would be to go with an LM337. It can do 1.5A in one pkg with minimal support components. It even has internal thermal overload protection.
http://www.westfloridacomponents.com/mm5/graphics/ds5/LM337-ONSemi.pdf

Edit: Here is also a 10 pack of the 7135's rated at 1A. You can see the one "open" area. If you strip one 7135 from the other board you have the PCB and the 1.4A you need already built! If you read the comments you'll see where ppl do this as they are all in parallel. I'm sure there is another offer with all 4 7135's in place & bulk.
DealExtreme: $16.58 AMC7135 1050mA Regulated Circuit Board for DIY Flashlights 10-Pack

If you do the DX offers, don't forget to use the forum link so the forum get credit for sales.

BShanahan14rulz · Oct 4, 2010

I were gonna say, as long as the Vf isn't too high, you could just use 7135's.

I think your biggest issue with those, though, would be reducing the voltage to the 6V max input of the 7135, if your diode has a high Vf at those currents.

What kind of build are you doing?

kiyoukan · Oct 4, 2010

okay i like the deal extreme one but i was kinda dead set on using 2 lir123a 3.7v battery's.
Is there any easy way to drop that last bit of volts?
Or should i go for a new battery?
This is a portable build

small lm317 driver advice needed

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