Still looking for a driver...

jbtm · Apr 4, 2011

Not getting anywhere really because people arnt answering and PM to Dr. Lava didnt get answer either.

I'm still looking around as to what driver i can use for my 1W IR laser diode. I wasn't sure if a microboost would be ok, to use on a diode like this. Since we know IRs run lower voltage, like around 2V. Id like to run this at exactly 1A.

So what drivers do I have avalible? Is a microboost ok?

I accidentally ordered the 18650 host, cree, in the smaller AA size. Luckily i can still mod it and fit all i need inside it perfectly.

LarryDFW · Apr 5, 2011

jbtm;

You don't need a "boost" driver at all.

A LM1117 driver will supply the 2VDC the IR laser requires:

http://laserpointerforums.com/f39/fs-lm1117-based-linear-driver-1-3a-fixed-60213.html

LarryDFW

rhd · Apr 5, 2011

Not only do you not NEED a boost driver, but as far as the Microboost goes, you CAN'T use it. The microboost is boost-only. It won't buck the voltage down. That's a problem.

I agree with Larry's suggestion 150%. The driver he linked you to is sold out, but it's super easy to create a DDL circuit. Grab this:
2 Watt 1.2 ohm 1R2 Carbon Film Resistor R 2W (10) - eBay (item 230584612257 end time Apr-11-11 21:03:58 PDT)
And these:
10 PCS AMS1117-ADJ SOT-223 LM1117-ADJ 1117 ADJ 1A | eBay

And you'll have a 1040 mA driver

HIMNL9 · Apr 5, 2011

^ no ..... you have TEN 1040mA drivers

Seriously, don't forget some capacitors, and for 1A, better use a good heatsink, or 2 of the regulators in parallel (still heatsinked)

EDIT: also remember that for the SOT223 version, the current limit is 800mA, and the dissipation limit is less than 1W (1W with copper plane dissipation), so consider also these parameters, if you don't want that the driver go in overheating protection after few seconds

rhd · Apr 5, 2011

I actually think he can get away without crazy heatsinking if he does two of them in parallel with balancing resistors. 500mA each, and basically just 2V or less of voltage to dissipate. You're looking a 1W of heat. That's not a ton. Not compared to running a 445 off 3x cells in a ddl lm317 setup at 1.5A - Hello 10W of power dissipation!

HIMNL9 · Apr 5, 2011

Uhm, but 1.25V drop on the resistor, plus 1.2V drop on the IC itself, does not left a bit too less voltage for the diode, with a single 3.7V cell ? ..... when it's fully charged it's enough for an IR, but at medium value ? .....

jbtm · Apr 5, 2011

Well hopefully i can manage to pop this into a 15mm diameter pill for a host. You see, had a microboost work, things would be just great because that board would fit in this like a beauty. But, I will see what I can do. Maybe able to fit a LM117 in here with other parts, the pill is solid brass and was origionally thermal pasted for a LED...so I can do the same for the regulator, thermal paste it to the brass pill.

will see what I can come up with. For testing I did run it on a LM317 and a 1W rheostat. Worked.

See, I miss ordered a host. So It's a 14500 battery size host. Plenty big for a microboost for sure. Will try for this.

Only issue with this is, cant i risk draining my battery way under without a protected 14500?

HIMNL9 · Apr 5, 2011

jbtm said:
..... Maybe able to fit a LM117 in here with other parts .....

Be careful to not confuse the part numbers, LM117 is not a low dropout regulator ..... only LM1117 is LDO

jbtm · Apr 5, 2011

HIMNL9 said:
Be careful to not confuse the part numbers, LM117 is not a low dropout regulator ..... only LM1117 is LDO

I use LM317s all the time for 1.5V - 3V laser power supply units. Just not hosts. Works from 1.2V to 37V, can adjust 1.2V to 37V. Thus, it's fine to use a LM317 for a laser driver, as well, I always have. Plus, it fits.

HIMNL9 · Apr 5, 2011

^ no, i mean ..... if you are planning to use a single Li-Ion cell, do not confuse the two regulators, also if the part numbers looks similars ..... LM117 have an internal dropout of 2.5V, LM1117 have an internal dropout of 1.2V

For two Li-Ion cells, there are no problems and you can use any of them.

jbtm · Apr 5, 2011

HIMNL9 said:
^ no, i mean ..... if you are planning to use a single Li-Ion cell, do not confuse the two regulators, also if the part numbers looks similars ..... LM117 have an internal dropout of 2.5V, LM1117 have an internal dropout of 1.2V

For two Li-Ion cells, there are no problems and you can use any of them.

LM1117MP-3.3 800mA 3.3V Low Dropout Positive Regulator - eBay (item 380188476633 end time Apr-09-11 01:23:22 PDT)

Can i use this? USA sold i s what i want. but says 3V? 3V max?

HIMNL9 · Apr 5, 2011

No, the 3.3 on the part number mean that this one is a 3.3V FIXED output regulator, and cannot be used as current regulator.

You need to get the ones marked ADJ (adjustable), for build a laser diode driver ..... like as example, these ones ..... or any other auction or component that specify "adjustable" or "adj" in the part number, NOT the ones that have a fixed voltage value.

EDIT: sorry, i've seen just now the "USA sold" part .....

anselm · Apr 5, 2011

I think those are fixed, you'll want something like this instead:
lm1117 adj | eBay
EDIT: LOL too slow

jbtm · Apr 5, 2011

Well I'm sure I can find some sold on the many sites I buy parts from. Figured that be nice anyways so I can get smaller parts anyways so it will all fit. Seems I can fit 2 of those LM1117 into a 15mm diameter pill and have them both mounted to the brass pill for heatsinking

rhd · Apr 5, 2011

If you're buying parts anyway, I'd just buy an LM1085, do the same circuit, and just use one, not two in parallel.

Two resistors also bulks up your build. If you're doing this in a 15mm pill, I'd say go with one IC (the 1085), the smallest 2W 1.2 ohm resistor you can find, and tiny 10uF ceramics on the input/output.

Will be a smaller build than two parallel 1117s. To accomplish two parallel 1117s, you double the resistor count right off the bat. You also add two balancing resistors. So you're looking at:

4 - resistors
2 - ICs

When you could go with the 1085 and have:

1 - resistor
1 - IC

And while the IC may be a slightly larger package, its still smaller footprint wise than two 1117s, plus you save a ton of resistor space.

jbtm · Apr 5, 2011

How can I figure what ohm resistor I would need though to run this diode at 1A 2v roughly anyways? What makes you say 1.2 ohms?

Will look into that. I also make my own circuit boards so I may do SMD capacitor and diode.

Still looking for a driver...

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