Hi, I've been looking around with not much luck trying to find some schematic for a driver which would have almost zero voltage drop. Using LM317 based driver will require power supply of at least 5V. However if I were to use one lion battery with 3.7 or two 1.5 batteries, I am out of luck here. In dx green laser pointers there is a driver like this: http://tech.section5.ch/news/wp-content/uploads/2010/01/laserdrv.pdf which works with 3V. I am sure it had to be here several times... So any links, guys?
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Are there some schematics for driver at 3.7V?
- Thread starter edy
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It really depends on what diode you plan on using. It is a big task to build a driver more complex than the lm317. How committed are you? How badly do you need to stick to 3-3.7V?
That diagram has so much wrong with it... they don't even have the basics down.
That diagram has so much wrong with it... they don't even have the basics down.
I am not sure what are you refering to, that diagram is pretty clear to me. However, I am not that dedicated, really, but it would be nice and useful. I just wanted to know if there is any proven solution so I wouldn't reinvent a wheel. Is there anything fundamental wrong in the diagram posted?
I don't see a problem in building a more complicated driver if I have a proper schematics..
I don't see a problem in building a more complicated driver if I have a proper schematics..
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Shunt should be lower; poor choice of op amp; output cap look like it will cause massive oscillations; The main current shouldn't need to go through the input regulator; previously mentioned connection failures... probably a few other points I'm missing.
Try Benm's design instead. I recommend 0.1 ohm for R4 and 10ohm for R3 and maybe replacing Q1 with a power mosfet. A small cap between the non-inverting input and ground should eliminate most of the noise from turning the pot. Circuits like these need a dropout of around 1V. So like I said, it depends on which diode you plan to drive.
Try Benm's design instead. I recommend 0.1 ohm for R4 and 10ohm for R3 and maybe replacing Q1 with a power mosfet. A small cap between the non-inverting input and ground should eliminate most of the noise from turning the pot. Circuits like these need a dropout of around 1V. So like I said, it depends on which diode you plan to drive.
Thanks for the reply. Okay, so how do you guys power your lasers? As an example - take WF501b host:
UltraFire WF501B CREE Q2 180-Lumen White LED Flashlight with Strap (2*16340/1*18650) - Free Shipping - DealExtreme
The ideal would be to put two 18650 (~2Ah) in, it's not possible however. Two 16340 (<1Ah) is not much juice and probably bad option if a diode takes about 1.5A at 2.2V...
Okay, so now to something more practical - advise me what to use, please. I mean driver, host and batteries.
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What're you driving, and at what current? If it's a red laser running at 350mA, maybe you could get away with using an AMC7135.
As I said, it is 808nm 1W diode running at ~1.2A, ~2.2V.
Something like this looks very promissing:
http://laserpointerforums.com/f65/switching-driver-445nm-diodes-53468.html
However LTC3454 has absolute maximum current 1.25 which is too low and I have hard time finding it around here.
That AMC7135... perhaps there is something simillar for around 1.2A?
Until then.. I am probably stuck with 2x3.7V battery.
Something like this looks very promissing:
http://laserpointerforums.com/f65/switching-driver-445nm-diodes-53468.html
However LTC3454 has absolute maximum current 1.25 which is too low and I have hard time finding it around here.
That AMC7135... perhaps there is something simillar for around 1.2A?
Until then.. I am probably stuck with 2x3.7V battery.
I found several buck regulators which could be used by Linear Technologies (Linear Technology - Parametric Search for Buck-Boost LED Drivers) or Texas Instruments (found on mouser.com), however I cant find them anywhere near and don't want to pay outrageous postage.
In near shop I found NCP3065 (CC regulator) which could be of use, but they don't have a smd version.
I will give a try to these: https://www.dealextreme.com/p/18v-5w-cree-circuit-board-for-flashlights-16-8mm-5-5mm-26110 ..
sounds promissing for $2; here's some tests My test results. - he used it with LED with Vf 3.49V, so I believe it could be used for LD. I'll post some info when they arrive (there is some talk about this driver around this forum already)
In near shop I found NCP3065 (CC regulator) which could be of use, but they don't have a smd version.
I will give a try to these: https://www.dealextreme.com/p/18v-5w-cree-circuit-board-for-flashlights-16-8mm-5-5mm-26110 ..
sounds promissing for $2; here's some tests My test results. - he used it with LED with Vf 3.49V, so I believe it could be used for LD. I'll post some info when they arrive (there is some talk about this driver around this forum already)
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I tried the DX driver with dummy load with voltage drop about 2.4 V and with one lion battery at 4.2V and it gives max about 800mA :-(. So this is not an option, obviously.
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rhd
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Edy - use the STCS1 chip.
Done
Done
New update I tried AMC7135-1400mA driver (sells on e-bay AMC7135 1400mA Regulated Led Driver | eBay $6 for 1)or DX (AMC7135 1400mA Regulated Circuit Board for DIY Flashlights 15-Pack - Free Shipping - DealExtreme $18 for 15) and it works... on fully recharged battery, it outs about 1.3A. I measured the battery drop on load and it's 4.21V -> 3.88V @ 1.3A so I believe that if I used better batteries, a much better and more stable result could be achieved.
I tried AMC7135-1400mA driver (sells on e-bay AMC7135 1400mA Regulated Led Driver | eBay $6 for 1)or DX (AMC7135 1400mA Regulated Circuit Board for DIY Flashlights 15-Pack - Free Shipping - DealExtreme $18 for 15) and it works... on fully recharged battery, it outs about 1.3A. I measured the battery drop on load and it's 4.21V -> 3.88V @ 1.3A so I believe that if I used better batteries, a much better and more stable result could be achieved.
