Line Drive™ - 15A Linear Driver for Labbies

[IWIRE]

Yes. Also on the way to a scope test are
these.

That's cool ! Looks good. That should help people to keep building. Maybe there is a silver lining to this drive shortage that's been plaguing us. Available options are always good. :beer:

 

[Rifter]

Re: Line Drive™ - A High Current Linear Driver

Yes. Also on the way to a scope test are
these.

These bring up the rear, < 700mA. I'm
especially hoping they will be good for 5mW
diodes, PHR, LPC, and everything in between.

I don't see a pot on those small ones, are they adjustable? Or do you just need to swap out the resistors to set the power?

 

[The Lightning Stalker]

Re: Line Drive™ - A High Current Linear Driver

I don't see a pot on those small ones, are they adjustable?

They will come preset for different diodes and
currents. I could also do an adjustable
version to range from 24mA to 690mA. I'm
hoping the fixed version will go up to 800mA.
Unfortunately, due to an error in board
design, I was unable to test these. More
boards are on order.

Line Drive™ initial scope test results:

@ 10A (3 1/3A/division)

It works! :wave: Sorta.
I need to play some more with resistance
values to get more adjustability in the pot.
Right now it's very touchy and goes from 5 -
10A in less than a quarter turn, but it is
limiting current.

I also need to get a bigger battery to get a
better idea of the actual current through the
diode, particularly under bounce conditions.
The battery is necessary since I don't have
an isolated probe. I tried floating the scope
with an inverter, but it just picked up a ton
of noise. If anyone else has some ideas,
please do share.
:thanks:

 

[IWIRE]

Congratulations on getting it going !
That's really cool ! Does it generate a lot of heat ?

 

[The Lightning Stalker]

Re: Line Drive™ - A High Current Linear Driver

The heat output all depends on how much
the supply voltage is above the voltage drop
of the diode. Right now, the way I'm
running it, the supply is 12V for lack of
anything else, and the Vdrop of the test
load is 5.6V @ 10A. That is a 6.4V
difference, so about 64W of heat that has to
be dissipated by the driver, which is quite a
bit. Ideally, it would be fed by just enough
voltage to keep it at the setpoint, and
maybe a few tenths of a volt more. That
would bring it down under 20W, which runs
cool on a 2" x 2" finned fan cooled heatsink
or a slightly larger one ambient.

Once I get all the kinks worked out, the 9
turn pot version is going to replace the
old LM338. If nothing else, it will be great
for testing diodes.

 

[IWIRE]

I've noticed that playing around with an LM338. If I get my voltage right the heat is tolerable. Any drive configuration is becoming useful for me. I finally got my lathe fired up a couple of weekends ago and I will be getting a mill soon.

I'm just going to make my host around components instead of being locked in to components that fit a host.

 

[The Lightning Stalker]

Re: Line Drive™ - A High Current Linear Driver

Yes, exactly! This is how a linear driver
works, bleeding off the excess voltage as
heat. The more voltage, the more heat.

Increase the voltage until the current stops
rising and maybe give it 0.2V more. That's it.

I'm also hoping to have a continuous positive
version of the small ones. More boards are
on order.

 

[IWIRE]

Thanks for the info :beer: They look really nice. Great job ! Members spitting out drives left and right are an inspiration for me to stick with it till I get it.

 

[The Lightning Stalker]

Re: Line Drive™ - A High Current Linear Driver

Thanks. I did some more testing on the Line
Drive™ today and swapped out some
resistors to fix the pot adjustability issue. A
15A setting is now a full turn on the pot
instead of 1/4 turn.

I also did some dropout voltage testing.

Vld + 1.30V @ 4.80A
Vld + 1.73V @ 6.50A
Vld + 3.22V @ 7.08A

The knee in the curve begins around 6.5A.
So it looks like the first few boards will be
this 6.5A version. I have some ideas for
getting all the way to 15A.

Then there are these.

It's just a simple switch board for adding a
pushbutton tactile switch to pen builds or
whatever. The switches are sealed and the
button part is made of silicone. They have a
distinct feel and give a different impression
from the standard pen switch. They are
rated 100mA, which is still better than the
50mA ones found in the cheap eBay pens. I
have tested them at up to 500mA and they
seem to work fine no problem. The one in
my DX pen is still going strong after over 8
months of regular use. Oh yeah, and they
do have a preferred polarity, which has been
marked on the boards.

 

[The Lightning Stalker]

Re: Line Drive™ - A High Current Linear Driver

I was finally able to build and test a few of
the small drivers. They work great, but drop
2.2V @ 168mA, so they are better suited to
lab builds in this revision. I have found
another chip though which will hopefully
produce results acceptable for handhelds.

If the continuous positive produces similar
results, it would still be great for the case
positive 638nm diodes, even in handhelds
since they run at 40mA.

 

[rhd]

Re: Line Drive™ - A High Current Linear Driver

I was finally able to build and test a few of
the small drivers. They work great, but drop
2.2V @ 168mA, so they are better suited to
lab builds in this revision. I have found
another chip though which will hopefully
produce results acceptable for handhelds.

If the continuous positive produces similar
results, it would still be great for the case
positive 638nm diodes, even in handhelds
since they run at 40mA.

If you're dropping that much voltage across the sense resistor, why don't you just change the scaling of the current sense monitor and use a lower resistance sense resistor?

 

[The Lightning Stalker]

Re: Line Drive™ - A High Current Linear Driver

If you're dropping that much voltage across the sense resistor, why don't you just change the scaling of the current sense monitor and use a lower resistance sense resistor?

That is a definite possibly, with a separate
current sensing chip instead of trying to do
it all with a single device. I was trying to
keep it simple and low parts count vs. the
Line Drives.

 

[LSRFAQ]

Re: Line Drive™ - A High Current Linear Driver

FYI:

You have no safety circuit on the potentiometer input. As multiturn potentiometers rotate, the wiper periodically lifts off the spiral coil. It may only be for microseconds or milliseconds, but it does happen. This can result in very fast high current spikes. Just an FYI to watch out for. So best to adjust this with a diode simulator for the load.

Steve

 

[The Lightning Stalker]

Re: Line Drive™ - A High Current Linear Driver

On the line drive? A test load is a good idea
with any driver, especially when it's meant
to power an expensive diode. I haven't
given up on them yet.

 

[IWIRE]

Is it common to adjust a drive terminated to a diode ? I've never tried that with any drive. If the output doesn't end up as expected, I always desolder the diode, hook it back to my test load and figure out where I screwed up.

 

[The Lightning Stalker]

Re: Line Drive™ - A High Current Linear Driver

I'm working on another revision of the 15A
driver. Hopefully this time it will get all the
way up to 15A.

Watch this space for updates.