Single cell driver that can run LOCs adjustable or not...dont care

[steviedezie]

I've got some good ideas on hosts for reds but ran into driver issues. Since these hosts im looking at are all single cell, i've hit the barrier. Boost drivers will direct drive if input > output. Buck drivers have a voltage drop of at least 1.2V which will not allow the driver to send enough power to a LOC, thus not hitting the full potential of the diode. Also, I should be getting the new lpc-826's and those can handle 500mA+ so with Vf of like 3.3 so thats even worst. LOC's Vf is too low to boost, too high to buck.

What Im looking for is either, a buck driver that has a voltage drop of less than .6V or driver that can boost from 1.2V AND a brand of NIMH's that can handle 2.2A current draw. I tested several boost drivers on a test load and at 1.2V they draw over 2A to supply 450-500mA at 3.2V. The 4 brands of NIMH's I've tried have yet to be able to supply that. I've gotten the panasonic ones to do it, but for like 2 minutes...then it drops sharply.

 

[bluuray]

jibs driver can run a red with one cell..
just replace the resistors to set the current where you want it

 

[rhd]

jibs driver can run a red with one cell..
just replace the resistors to set the current where you want it

No it can't, not at 500mA. I mean, I shouldn't say that for certain, because I haven't tried it, but I know the circuit and IC fairly well, and it won't be able to deliver 500mA to a LOC. Here's the killer dilemma:

- At 500mA, a LOC (or LPC-826) is going to require a voltage of around 3.6 to 3.8V
- For a single cell setup, with a linear driver like jib77's, you need a voltage drop of about 0.3 to 0.5V or less.
- Every DDL linear driver I've seen, drops more than 0.3 to 0.5 V.

To be clear - jib's driver WILL run red diodes off a single cell, and should do it fairly well. But it will only run the red diode (and jib, please correct me if I'm wrong) at the lower portion of the current range, when the LOC's voltage requirement is lower.

This is the "annoying" range for DIY single-red builds. In my mind, you probably need either a boost/buck pre-made driver (OdicForce *might* have some that would work) or a buck driver. I'm fairly certain that a buck driver *doesn't* have any dropout (just has efficiency losses). I think dropouts are just a linear driver issue.

 

[steviedezie]

ahh rhd to the rescue. I meant linear driver up there in the first post. linear drivers give you the problem of voltage drop.

anywas. Odicforce drivers are buck/boost??? i have 2 of their boost drivers here on hand...will test to see if it bucks as well.

on another note, I think I might have to pay thesandwichshoppe visits again...they got some nice buck led drivers for about 12 dollars...not bad considering they only require .25V to run the circuit. That leaves 3.9V for the diode.

EDIT: ok I found out that the Odicforce drivers do buck as well as boost. Though these drivers werent meant to hit over 400mA... bucking or boosting. It got hot after 30 sec on bucking 4.2V down to 3V at 500mA. I guess its possible to use these as long as you heatsink the driver...and i mean heatsink it good as hell.

 

[rhd]

I'd take this:
Variable Current Step-up (Boost) 405nm Laser Driver Board - Detailed item view - OdicForce Lasers Online Shop

Which I think is boost-only, but designed for up to 500mA. Then I'd add a 1N540X diode in series with the LPC-826 (or LOC) to keep the driver's output voltage always above the battery supply, so that it's always boosting.

Sounds good in theory.

 

[steviedezie]

thats the exact same driver I have on hand. I dont know if it was meant to buck or not but it does do it. I've bucked at 500mA and it got hot fast. At 400mA it got hot after 30 seconds. I dont know if im breaking the driver by doing this, but it current regulates even when input > output.

my test was done on a 3A power supply in constant voltage mode. voltage was at 4.2 and testload was set to red at 2.9V. Weird that it also bucks. but I'll heatsink the driver and run a 2 minute test to see if it can last.

 

[Wolfman29]

It may not actually be bucking. Bucking is when the current is regulated no matter the voltage. However, since your voltage is constant (via constant voltage mode ), it may very well not be bucking but just direct driving.

 

[steviedezie]

im pretty sure it was bucking since the pot still allowed me to adjust current. The power supply can do 3A but it was only drawing .55A. assuming 80% efficiency, it does seem like it was bucking. Although I dont know why the driver got so damn hot after only 30 sec.

I think it was a convenient bonus that it did it manage to supply a constant 2.9V at 430mA to a test load. I havent tried hooking up a diode yet but I might get some actually LOC's to test.

EDIT: the voltage at the PSU was constant...not at the driver output. also, voltage change at the drivers input did change output current but only slightly. a drop in 0.5V at the driver input caused a 30mA drop in output current. That might not be completely bucking but its good enough for me. Only a real LD can prove if this driver will work with a LOC or not.

 

[jib77]

I did run a single cell test a while back ... these are the results with a 3V dummy load:

4.2V = 430mA
4.1V = 420mA
4.0V = 410mA
3.9V = 400mA
3.8V = 380mA
3.7V = 360mA, drops out of regulation after this

 

[Morgan]

This may not be the answer to your question but I've had some success using microboost drivers with 14Nxxx diodes in front and in series with the LD. These satisfy the forward voltage of the driver specs and as long as you insert the correct number of diodes between the driver and the laser diode you'll be fine. You'll have to work out the numbers yourself but, for example, if you want to run a LOC diode with a Microboost with a 18650 battery, the diodes in series drop the required voltage at the output enough for the LD rather than trying to drop them before the driver, [EDIT], (I supposed it was possible to put the diodes between the battery and the driver but you then drop below minimum input voltage if you try to do this for a green). It works as I've done it. Diode choice can be different depending on the laser diode you are using but it works fine. Not efficient for battery life maybe but it works. Just tack a few in series with your LD and you can run a Micrboost to drive an LOC happily.

M