The Lo-D Driver

[Hiemal]

Hey guys.

I recently had septoplasty done on my nose to straighten out my septum, drain out my sinuses and fix a few other things that were causing me breathing problems.

Before I got the surgery done though, I've been working on a fresh new linear driver design, something I'm quite positive everyone should enjoy.

I'll upload some pictures of it in a few days when I feel better, so you know it's not just vaporware. I couldn't wait to share it with you all!

So, the specs.

It's not a tiny board by any means, it measures 23 mm by 11.8 mm. The new revisions of the board I've made do measure slightly smaller, shaving just a few mm off the sides at 22.5 mm by 10.55 mm.

Super low drop out voltage, averages around 700 mV - 1 volt, depending on what output current you're using. More current = more v-drop.

Fully adjustable boards. Send me a PM for what kind of current range you need and I'll tailor a board to it the best I can.

A max output current of a whopping 5 amps. Now, please, keep in mind, this IS with two li-ion cells. Because it's a linear driver it will dissipate a great deal of heat when using it at such high currents with two batteries.

Continuous ground.

Using one li-ion battery it can push out approx. 3 amps into a 3 volt load, while dissipating very little heat.

Please, keep in mind since IR diodes forward voltage level is below the minimum operating voltage for the current sense op amp, they are NOT supported for use by this driver and will be overdriven beyond their capability. Please use one dropping diode in series with your laser diode to bring the forward voltage up enough.

Price point should be around $14-$15.


Hope you guys'll like it.

 

[Pi R Squared]

Re: New Linear Driver Design coming...

That sounds great Le Quack, we can always use another driver to choose from. If the price goes as low as $14 then that's cheap, especially if it can really do up to 5A. Looking forward to seeing this.

I too have some bad health problems including trouble breathing at times, I hope you are able to recover soon.

I think you should call it "Le Quack Linear" or "The Quack Linear".

Alan

 

[bdgreenb]

Re: New Linear Driver Design coming...

this thang sounds juicy i also think XXX-drive should not be the standard for naming drivers.
i say you call it "Dr.Q"

 

[rhd]

Re: New Linear Driver Design coming...

I'm wondering - what's your target use case?

 

[Hiemal]

Re: New Linear Driver Design coming...

I'm wondering - what's your target use case?

Well, I went into this trying to fill a certain gap that I felt was left open; a cheap, versatile driver that performs well, across a wide band of circumstances. Because of its extremely low voltage dropout it allows for higher runtimes, and single cell useage for high power red builds, and dual cell useage for those high power blu-ray builds. With those two cases you get very little heat dissipation since the voltage in and the voltage out can be very close to eachother without sacrificing too much run time. Of course it can also be used for other builds too, but the heat output will be increased a bit.

A good number of previous linear drivers built before either had excessive voltage dropouts, poor heatsinking ability, or very few current selection options (like every 800 mA or whatever)

With this driver I'm fixing all three.

 

[Hiemal]

Re: New Linear Driver Design coming...

So as promised, here's some pictures of the drivers!!

I've done a good amount of testing tonight and played around with values/components on the boards and i finally fixed the oscillation issues.

I made 6 boards that are adjustable from 1.8 amps to upwards of 4 amps (the max is heavily dependent on your input/output voltage) and 2 boards that are adjustable from 700 mA up to 4 amps again (though I don't recommend running these as high simply due to the sense resistor dissipating too much heat).


Also, remarkably, when I tried to measure for output ripple, I could not find anything... (this may be because i was measuring it off of the current resistor on my test load?) But, it IS a linear driver, so I guess I'm not too too surprised.

 

[Hiemal]

So I did some more testing/fooling around with the drivers today, and I managed to fix every single issue with the boards and add a really obvious soft start to the board with a very simple addition.


All boards are now fully useable across all of their current capabilities, and do not produce any oscillations, spikes or any of that nasty business.


They also have full thermal protection (if the driver gets too hot the output current will slowly reduce until it reaches a certain equilibrium).

I also did a pretty significant revision to the boards, changed the parts layout and also added a sizeable blank heatsink spot on the back to allow for more efficient heatsink attachments. Also removed unnecessary pad spots, and generally just made the boards better, wider traces and more vias. I'll be making these in a little while once the initial 6 boards sell.

Also check the original post for some more information.

 

[rhd]

Very cool!

Just a heads up - I of course don't know your schematic, so can't say for sure, but based on the photos, description, and some educated guesses, I think you may find that these won't work as-is for IR laser diodes.

PM me if you want me you explain. Happy to.

Cool project!

 

[Alaskan]

Why not use a dropping diode in series to bring the output down enough for an IR diode?

 

[Hiemal]

Why not use a dropping diode in series to bring the output down enough for an IR diode?

That is one way to work around it, certainly. Hadn't thought of that, funnily enough.

 

[Alaskan]

That's what I've been considering for a work around I need to drive one.

 

[Hiemal]

Well hey, I don't mean to toot my own horn but this driver would be fantastic if you're looking for a really high current driver, esp if the input/output voltages are similar.

Since you're using an IR diode, and you want to add voltage to make it useable I'd definitely use a schottky diode. This'll add roughly 0.4-0.5 volts vs the 0.8 of a normal silicon diode and would give you more leeway in terms of runtime.

To calculate the power dissipated by a linear driver is pretty easy too.

It's basically Vbat - Vforward * current. With the bare minimum difference (aka, the 1-1.1 volt or so dropout difference) at max current, you're only dissipating about 5 watts.

 

[Alaskan]

Can several be paralleled together to increase the total current without using blocking diodes to isolate them from another? Although for my need, a blocking diode might be the perfect answer anyway, to get the voltage down to 2.0 VDC or so, plus or minus a couple of tenths. How does the start up current look to protect the laser diode?

 

[Hiemal]

Can several be paralleled together to increase the total current without using blocking diodes to isolate them from another?

I don't actually know the answer to this, i'll give it a test tomorrow. The drivers have continuous ground too by the way.

Although for my need, a blocking diode might be the perfect answer anyway, to get the voltage down to 2.0 VDC or so, plus or minus a couple of tenths. How does the start up current look to protect the laser diode?

You're putting the diode in series with the laser diode to bring it's forward voltage up not down. IR laser diodes have a typical Vforward of like 2 volts anyway, right or am I mistaken?

And the start up current for the laser diode is silky smooth. I can actually watch the current rise on my oscilloscope.

 

[Alaskan]

OK, these might be what I need if I can put several of them in parallel to produce up to 16 amps total current.

Since I would be using a diode on the output of each regulator to reduce the voltage fed to the LD down to 2.0 VDC, I don't need a test confirming they can be ran in parallel, the dropping diode from each regulator would then also be a blocking diode to isolate them from another. I've used diodes in series before to drop the supply voltage by small amounts with other circuits I've built, easier to do that than use a voltage regulator.

I've paralleled up to 12 constant current regulators in the past using a blocking diode from each regulator and it worked great, but those were 12VDC boost CC regulators to produce close to 40 amps at 35 VDC. It worked great, although I had to change out a couple of the regulators which didn't want to play fair with one another in the sand box, perhaps were flaky to begin with.

 

[Hiemal]

OK, these might be what I need if I can put several of them in parallel to produce up to 16 amps total current.

Holy jeez, what are you making if you don't mind some curiousity? 16 amps of current is quite a lot of juice.