Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

LPF Donation via Stripe | LPF Donation - Other Methods

Links below open in new window

ArcticMyst Security by Avery

Dual buck drivers?

Grix

0
Joined
Dec 9, 2008
Messages
2,190
Points
63
Quick question, is it possible to use two buck drivers in parallel for a single diode, without any trouble?

Say you want to tame the the new 3.5W 445nm diode, you'd need like 3.5-4 A, I don't think there is any driver small enough that can handle that current. So if dual drivers doesn't work, what other options are there?
 





Joined
Jan 8, 2009
Messages
3,145
Points
83
The super X-boost will run that with ease. Remember to use 22 to 20 gauge wire. Hope that it fits for ya.
 

djQUAN

0
Joined
May 27, 2013
Messages
1,154
Points
63
If it's a continuous ground or continuous positive driver, it should be possible to parallel two.
 
Joined
Sep 12, 2007
Messages
9,399
Points
113
To elaborate a bit on Mr. quan's post, often the drivers will do the switching on the positive side and sense the current on the negative side. So having them in parallel means their sense paths interfere with each other, and one ends up working much harder than the other, which will eventually kill it. To see if your driver has a continuous rail, check continuity from Input (+) and output (+), and also from input (-) to output (-).
 

djQUAN

0
Joined
May 27, 2013
Messages
1,154
Points
63
I don't think a continuity check would be reliable in testing a continuous ground/positive since some drivers have the switching regulator circuitry on the positive side and the sense resistor on the negative side. The sense resistors are usually a fraction of an ohm or so which will show as a nearly short circuit in the continuity check.
 
Joined
Jan 8, 2009
Messages
3,145
Points
83
Or you could put on a jewelers glass and follow the pads path. That's how I've allways done it..
 
Joined
Jan 29, 2014
Messages
12,031
Points
113
I have a cheap solution to a higher amperage constant current source, I've done it before to limit the current to an 800 watt array of LED's all running at 32 VDC. All you need to do is parallel as many constant current power supplies as you want to a single bus which are isolated from one another. i.e. if you need 16 amps you could use four 4 amp current limited power supplies, set each to a maximum of 4 amps out and isolate each one from another using diodes feeding a common bus, set the voltages from each to closely match one another too, of course. In my last LED project I just set my voltage regulators to 32.0 volts across a 100 watt 10 ohm resistor, that way no power supply could have more than 3200 ma or 3.2 amps demanded from it, setting the current limit to that point, after the voltage was adjusted to 32.0 VDC. I took the voltage measurement from each supply AFTER the blocking diode, that way I didn't have to worry about small differences between diodes at the full current draw I was going to have.

This worked for me before without problems and no one power supply can have too much current drawn from it as they all have their current limiting set the same. There will be minor differences between power supplies which can cause some unbalance so I just ordered several extra ones and was able to find some which were close enough to balance out fine between one another at the operating load without any strange looping going on. This wasn't really necessary because most of the 12 power supplies I used were close enough except for one odd one out power supply that was acting wierd when paralleled like that but I found that the current drawn from each is more stable if you match them, they can "act up" and you can get some strange current loops if they aren't close enough to one another, even though all of them had a common negative. Additionally, some small super capacitors across the bus can help if running close to the rated current outputs, if they are big enough and you don't need a 100% duty cycle over the time the capacitors can make the difference.. Also, a 5 to 10 percent constant load across the bus is good to have too, depending upon some factors but if using batteries, I wouldn't waste the power.

I am sure some power supply designs are more stable than others for this arrangement, some won't give any problem at all, others might. These were all 600W rated switching step-up DC-DC power supplies operating off of 12 VDC to produce 32 volts DC which are more finicky in this mode of operation than just a straight DC current limiting circuit board and batteries (my step-up units would only produce 3 amps out each at 32 VDC, extras were used to give lots of overhead). You wouldn't need a step up switching power supply with voltage and current adjustable outputs for a laser diode, as low of a voltage as they use. Just using a battery with a small linear voltage regulator board with current limit adjustments would be much easier to deal with and you probably won't have to concern yourself with much except for setting the voltage and current limitings identical as well as the outputs from each board being diode isolated from one another. Oh, I didn't do so with my project but it would be a good idea to have the isolation diodes matched for voltage drop too, or as close as you can reasonably get them, mine must have been close enough as they were, since it didn't cause a problem I didn't look into it but for a laser project, I'd deffinately check that. Also, you must take into account the voltage drop through the blocking diode(s) to determine the voltage you need from your battery or power supply prior to going through it to have enough for your laser diode on the paralled output bus side and use large enough wire to the laser diode so there is a minimum voltage drop there too. You obviously won't be using a sense wire on the laser device side of the reverse blocking diode, so no issues there.

I am not claiming this arrangement will work with all configurations, but you can configure your circuits so it will work. Someone ought to put some of these boards together in the size of a battery with mini screw driver current setting pot adjustments all along the side to make sure the current drawn from each board all match up, some kind of output test points for each individual circuit board to be able to match them up, if they go out of calibration. You could also have a main voltage regulator built into them too, adjusting the voltage input to all of the current regulators (really just individual looped voltage regulators with paralled outputs through blocking diodes) to make the thing work for a large range of lasers, allowing a lot of variability for the batteries used with them at the needed output voltage and current. It would also be nice to have slip on sleeves so they can work with larger diameter battery tubes too, perhaps with metal springs wrapped around them to help transfer heat to the tube. All of that said, better to just use a single regulator capable of high enough current to cover a range of laser diodes and build it the size of common batteries used in laser pointers. For my project I need close to 15 amps, so paralled boards might be easier, using existing designs with a couple of tweaks to them. I like the idea of a battery sized adjustable constant current regulator to simplify home brew pointer designs. Of course, for professionally done pointers, you could save some length building it into the head of the pointer with better cooling too, compared to having it burried in a battery tube.

Here's an example of the kind of constant current regulator I am thinking might be good to parallel together in a tube: http://www.amazon.com/Shanhai-445nm-450nm-Driver-Supply/dp/B00HFVQMWC/ref=pd_sim_sbs_indust_6 - Just as an example, I don't know anything about this particular unit. Key to making this work is to be sure not to run any individual current limiter too close to it's max power because due to some variables, some will likely draw a bit less than others (never more than rated current, if properly current limited). I'd have a conservative margin of 25 percent less than maximum allowed current draw from any unit, in other words, all the boards together should be rated for 25% more current draw than you will actually be using as a total current draw, even better pull only 50% of the maximum allowed current load if you can (Some engineers already build this margin into the design anyway, it just depends on what they have done). You can try running them closer to maximum, but this gives some wiggle room due to variables which otherwise might end up being a pain in the backside to balance. With some experimentation I am sure you can find out what you can really do or not, or how close to maximum current rating you can really go without concern of a board taking more than its fair share of the load, but in the end, it won't matter that much because they are current limited not to exceed their individual rated outputs, I just like everything to run on the conservative side, this means a lower failure rate if ambient temperatures are higher than normal etc..

As a last note, all I can say to anyone who might think this won't work is it has worked for me with high power LED's, I don't see why it won't work with laser diodes, with a few extra tweaks I might not realize right now as I am not a laser tech, just a RF technician with lots of DC power supply experience. If anyone can add something I'm not getting, please let me know as I could use the help for when I start putting parts together for my own 15A+ laser diode project. Most of this post is cut and paste from another thread on my project, but I thought I should copy it here as it directly applies to the thread.
 
Last edited:




Top