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Continuous positive?

cappernicus

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I've been gone for a while so I'm kind out of the loop with what's happened in the last couple years. After a good couple hours searching I did not find any useful information, so here's the thing:

I have an m140 445 that I'm working on. Because of the way I'm making the case it has to have a continuous positive driver, and it can only run on a single battery. The only continuous positive drivers I've found are linear, which wouldn't wouldn't be able to drive a 445 at 1W+ off a single battery correct?

Does anyone know of a good small continuous positive boost driver? Or know how to build one?
 



The Lightning Stalker

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Driving an M140 it shouldn't matter either way. Neither junction of the diode is tied to the case, so wiring
issues aside, it doesn't matter which way your battery goes. Just be careful that nothing metal on the
driver board comes into direct contact with the host and you should be fine.
 

cappernicus

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There is a reason it needs to be continuous positive. It has nothing to do with the diode pins, but rather the specific way I am building the laser.
 

The Lightning Stalker

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What I mean is that it doesn't make any difference to the diode or driver how you build the host. You can
use any driver you want.
 

cappernicus

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Sorry, I should probably explain more...

Because of the way I am building the host, the battery has to be oriented so that the positive end is at the front of the host (diode end), and the driver has to go at the back end of the host behind the battery. Unless I run wires down the length of the battery (which I can't) I have to use a continuous positive driver. Believe me, if there was an easier way I wouldn't be asking this question.

The AMC based driver would be an excellent option, except that it is a linear driver and wouldn't be able to give the diode enough voltage to run it at 1W correct?
 

Hemlock_Mike

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Capp --
What LS is telling you is that the diode connections are "floating" - damn,
that's an old ham radio term. The only connections related to +/- are the
two diode wires.
HMike

"Floating" = isolated
 
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cappernicus

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I know what he is saying. I'm not stupid. I understand that concept very well, as I am not a beginner to laser building. You don't understand why it's necessary because either you haven't thought it through, or I've done a poor job of explaining it.

What he said is normally true. IF the driver is in between the battery and the diode then I could do it either way just by reversing the battery. The real problem is that the driver has to be at the rear of the host, and that I cannot reverse the battery.

I was going to post a diagram, but I'm not sure how to insert images. So, you can just assume I'm crazy and have no idea what I'm talking about, or you can think through it, or sketch it out if you have to.

I did not want to start an argument. All I want to know is whether or not there is a continuous positive boost driver somewhere that I can buy, or if there is a schematic I can use to build one.
 

foulmist

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you can upload a picture to photobucket or other free image space site and link it here.

I don't think you will be able to find a boost driver that uses the negative side to boost the voltage. If you can use two smaller batteries in series say 2x 16340 instead of a single 18650 would do the trick with a linear driver.
 
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The Lightning Stalker

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the driver has to be at the rear of the host

Ahh, well there is the big detail I missed. I don't think there is any possible way to do it
besides linear. A switch mode driver needs to have access to both supply "rails." It cannot
simply scavenge off the voltage it drops. One reason is that the diode drops so much voltage
itself that there isn't enough left to generate a reference or even do something simple like
switch a MOSFET. With a single cell design it becomes completely impossible. There isn't
even enough voltage to start the diode going in the first place. Even if you had enough voltage
to overcome the drop of the diode, you would have to do things like pass voltage backwards
through the battery or overvolt it. Lithium cells can be dangerous even under normal
conditions. Try and do something like that and you could end up with a pipe bomb. So yeah
I believe you have effectively shot your build in the proverbial foot by limiting it in this way.

About the only thing that would work in there would be a red or IR diode run off a low dropout
regulator such as the LM1117 or AMC.
 

foulmist

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if you think about it any driver - linear or other needs both contacts of the battery. you can't just dismiss one or the other. So if you have case positive you also need the ground of the battery to have access to the driver.

if you could post a diagram of your project it would be much easier to help you out :beer:
 
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BShanahan14rulz

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How about some ribbon wire and few layers of kapton inside the battery tube, like how they do it with protected batteries? This may be too "hacky," but would allow you to get your + feed back to the driver.

What about small drivers that can fit in the back end of an aixiz module, do you have room for that?

Sometimes, drivers don't like having their loads too far away from them. I dunno why, I ain't too good at 'lectronics
 

djQUAN

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If there's a cap (with the right values) in the input and output, lead lengths shouldn't be a problem. Unless the loop stability of the driver is marginal.

Long wires add additional resistance and inductance that alters the loop stability of the circuit making it unstable and in some cases, oscillate which can cause current/voltage overshoots which is bad.
 




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