FREE DIY open source BOOST driver!!! Tested & working!!

[benmwv]

Hey everyone. So today I have a physics lab (I'm a physics/math double major) on AC circuits, meaning that I get to work with an O-scope. The good part about this is that I can bring in my own rendering of this circuit and test it out there in some spare time!

My circuit is nearly identical to the one that they did except I am using a 6.8uH inductor (only large enough inductor I have on hand and it works well enough) and I changed the layout so it fits on a single-sided 16.2mm round PCB. Anyway, I'm bringing my test load and I will use the PSU there, and all should go swimmingly!

I tried using a 6.8uH inductor and it didn't work very well. It couldn't reach 1A. 10uH seems to be the magic number

What current are you getting?

Im pretty sure that there will be more ripple with a lower inductance also.

 

[Wolfman29]

Hmm. That's odd. I was able to reach 1A with this inductor. :thinking:

 

[tsteele93]

What is the purpose of the inductor in this circuit?

 

[Wolfman29]

In a switching regulator, the inductor converts excess current into more voltage (for a boost regulator) and excess voltage into more current (buck regulator). See, what happens is that the switch closes and the inductor stores charge in the form of an internal magnetic field created by the windings of wire. However, then the switch is closed and, because of the schottky diode in series with the inductor, the current cannot flow backwards and thus must flow forwards in the SAME direction as the incoming voltage (for boost regulators), thus adding the stored voltage in the inductor into the incoming voltage from the input power supply. So a bigger inductor can "store" more voltage.

 

[tsteele93]

Thanks, I was trying to figure out what these were FILTERING, that makes more sense. I'm guessing bigger would be better except we are trying to keep size down to fit in our hosts.

 

[Wolfman29]

Yup That would do it.

 

[tsteele93]

Yup That would do it.

What would be ideal? Is there a tipping point where it starts to hurt the circuit? I see fairly high uH inductors in a small form factor that don't cost much more. Any reason not to go high?

Thanks for explaining this to me!

 

[chefla]

IMHO there is no tipping point. But I would keep an eye on the DC resistance of the inductor. For best efficiency you need an inductor with low resistance. Those inductors generally are larger in size due to thicker wire. Also, a higher inductance produces less current ripple. I always try to find the inductor with the lowest DCR and highest inductance that just fits my board, sizewise.
There are a few handy online calculators which will give you an idea about the needed inductance for your application. Try this link and play with the numbers. For the LM3410X/Y you could also get registered at national.com or ti.com and use their online simulation tools.

 

[rhd]

If you find a shorter inductor in the process, please let me know.

 

[tsteele93]

Yeah, that is my goal too. I want to do some builds here and I'd like to find a niche. One thing that I would like to do is try and over-engineer without regard to finding the cheapest parts.

Don't get me wrong, I don't want to make it so expensive that I lose money selling them - but I'm not really interested in turning a profit - this is just a hobby. So I would like to spend a little extra and have a really good product.

I feel like you already do that to a large degree rhd.

I want to use copper where possible rather than aluminum and I doubt that I will do too many builds using my own (or a modified version of your) driver - but if I did want to modify a flashlight driver to do modes (shhh!) then I would like to know what things I could do to make it more stable.

Unlike some builders here, I probably wouldn't be doing this with 2.0+ watt blues, so I would only need it to be safe for a diode that wasn't being driven to 150% of its rated output or anything like that. I would be looking more for novelty than absolute power.

Anway, that is my logic in asking some of these questions. It would be nice to find some higher quality components that cost only a little more, but add a lot more reliability and quality to the driver - if that makes sense.

 

[benmwv]

One thing you have to remember about inductors (other than the DCR) is that higher inductance means lower saturation current for inductors of the same size. So basically there is a tipping point for too high inductance and that is when it can no longer handle the switch current without saturating. This, combined with DCR is why we can't just use a 500uH inductor

One question I've had about inductors, in a buck configuration does the inductor need to be able to handle the max switch current or the max output current?

@Tsteele. I can assure you we didn't use low quality parts just to save a few bucks lol. The only thing I could see spending some extra money on is maybe bigger output caps, but that isn't needed and I'd don't think that will be a major selling point to people buying your builds

You really need to get off this "modified flashlight driver" thing.

 

[tsteele93]

@Tsteele. I can assure you we didn't use low quality parts just to save a few bucks lol. The only thing I could see spending some extra money on is maybe bigger output caps, but that isn't needed and I'd don't think that will be a major selling point to people buying your builds

You really need to get off this "modified flashlight driver" thing.

PLEASE don't think that is in any way what I am saying. If it came across that way then I apologize. You and RHD should know that I have a huge amount of respect for you both. I'm not suggesting you cut corners, I was referring to the idea of trying to build drivers with a budget in general. I am not talking about your driver specifically.

Also please understand that I am asking questions, not making accusations or pointing fingers. I am trying to understand things better. They are innocent questions asked out of ignorance and my desire to learn the answer to those questions and replace that ignorance with understanding.

I do not know what you mean by getting off the modified flashlight driver thing. Are you saying that I shouldn't pursue that avenue? Is it a waste of time? I just want to add strobe and low power modes. I see that Aixiz offers drivers with TTL controls, so I assume that would let me strobe but I don't know about lower power.

 

[rhd]

If you're just looking for strobe, you could do that fairly easily by using Sigurthr's pulse circuit, and any driver of your choosing:
http://laserpointerforums.com/f67/how-pulse-laser-70292.html#post1019899
Johnny made a PCB based on the design, and I tweaked it a bit and ordered my own.

In terms of this driver, I can't really say that there's much I would do to improve the *quality* of the driver itself. Most of the changes I would want in a better boost driver would essentially amount to just creating a new driver based on a new IC.

That said, if I was trying to make this as robust as possible, I'd expand the board size by 2 or 3mm in each direction, space the components out more, increase the trace widths (where appropriate) and use bigger caps.

 

[benmwv]

PLEASE don't think that is in any way what I am saying. If it came across that way then I apologize. You and RHD should know that I have a huge amount of respect for you both. I'm not suggesting you cut corners, I was referring to the idea of trying to build drivers with a budget in general. I am not talking about your driver specifically.

Also please understand that I am asking questions, not making accusations or pointing fingers. I am trying to understand things better. They are innocent questions asked out of ignorance and my desire to learn the answer to those questions and replace that ignorance with understanding.

I do not know what you mean by getting off the modified flashlight driver thing. Are you saying that I shouldn't pursue that avenue? Is it a waste of time? I just want to add strobe and low power modes. I see that Aixiz offers drivers with TTL controls, so I assume that would let me strobe but I don't know about lower power.

Sorry, I thought you were attempting to take a jab at lazereer or something.

Most LED drivers really aren't a good choice for laser diodes, but if you find a good one that regulates current and is stable you should be fine. If you are looking for quality though you should probably stay away from all chinese LED drivers.

You can control this driver by connecting a wire to the EN/DIM pin and pulling it low with a micro controller or a 555 and transistor, or whatever.

 

[rhd]

Actually, it would be kind of cool to do a fork where the EN pin's feed was split and exposed via two wire-pads, so that external triggering was made easy.

I think there would still be some trickle wasted power when off however.

 

[tsteele93]

Sorry, I thought you were attempting to take a jab at lazereer or something.

Dropped that, moved on.

I am genuinely curious about flashlight drivers being modded to be more stable as a driver for less than max power builds. I can see the general vibe is pretty against it, but I figured most of my hosts are going to come with a driver and if some could be modified to drive the laser and give me low power and strobe modes, then why not?

Most LED drivers really aren't a good choice for laser diodes, but if you find a good one that regulates current and is stable you should be fine. If you are looking for quality though you should probably stay away from all chinese LED drivers.

I was hoping that adding a cap to reduce spikes or maybe replacing a weak link in the circuit with a better part might yield a decent driver. Or even just stealing the modes and hooking them to a laser driver.

You can control this driver by connecting a wire to the EN/DIM pin and pulling it low with a micro controller or a 555 and transistor, or whatever.

That may be what I should investigate then. I think the strobe is a novelty, but could be neat. The low power could really be useful though. For example, my Survival Laser is 1.25 Watts. It is rare I can use it safely at that level. But if I had a 125 mW low power setting, that could be useful for times when I don't want to accidentally start brush fires in the distance.