DIY Super low dropout linear driver

justinjja · Apr 16, 2012

Thought You guys might find this interesting.
This is the "alpha" version of a driver that will be going in a 2D mag build.

I'm using a sparkfun slide potentiometer to adjust the current on the fly.
Planing on mounting the slide pot inside the host, just under the power button.

Its a fairly basic desing, Op amp controlling a mosfet, based on the input from a potentiometer, and the feedback from the current sense resistor.

Currently testing it with an XML led, because i wouldn't want to kill an expensive diode...

Results look good, Only need about 3.7V to get the full 1.8A across the XML.

Like I said, this is an "alpha" so you will have to excuse the mess

AnthoT · Apr 16, 2012

Re: DIY Driver for exteranly adjustable 445 Build

Nice I love the idea of the slide potentiometer for the host. You could turn it up or down anytime easily on the go, its real cool if you ask me :beer:

justinjja · Apr 16, 2012

Rebuilt it on a much smaller board,
Upgraded to a better mosfet,
Upgraded to a near rail to rail op-amp.

I'm now able to run the xml at 1.8A with only 3.2Vin, that is nearly no vdrop

I think that beats just about every other linear driver out there.

Now to scope it and make sure it is safe for my LD's

JLSE · Apr 16, 2012

Interesting idea.. I have a similar setup for my RGV handheld with 3 slides and linear control
and a single slide on a boost driven 18650 445nm build.

Im still looking for the space to fit the side clicky on the single, where the RGV build has a control box between
the body and the head.

Good luck on your build :beer:

justinjja · Apr 16, 2012

Thanks, I'm just hoping i can make the slide pot look natural on the maglight,
I think it will look good, but i wont know for sure till it is built.

Also hooked up the driver to a 445 diode,
Only needs 4.6V for 1.8A,
Thats only a .2V drop

sesam · Apr 16, 2012

Low dropout is always nice, What is the price for the components used?

justinjja · Apr 16, 2012

Price for me was almost nill.
The only part I actually bought was the potentiometer.

I just used parts I had laying around
using an lm317(cheap) as a 1.25 v regulator
The opamp and mosfet are probably a little pricey if you buy them,
and the current sense resistor is a bit overkill, but im using a .02ohm 1% 5W resistor

rhunsulrana · Apr 17, 2012

that's an awesome dropout rate! any idea how it'd do with a lower amperage build for a red diode?

also, any chance for a wiring sketch instead of pictures of your (gorgeously small) board?

BShanahan14rulz · Apr 17, 2012

That poor LED! Are you trying to keep it overheated so that it won't be too bright? ;-)

justinjja · Apr 17, 2012

This can be scaled up or down for just about any load,
You just have to pick the right Mosfet/op amp,
as well as the right combonation of resistors.

As for the led, I didn't leave it on for too long.
I made sure to turn it off once it started smoking.
JK LOL

Edit: for a red build you would probably want to switch out the 7805 5v regulator with a LDO 3v regulator
which would change the 5 in the formula to 3

rhunsulrana · Apr 17, 2012

justinjja said:
This can be scaled up or down for just about any load,
You just have to pick the right Mosfet/op amp,
as well as the right combonation of resistors.

As for the led, I didn't leave it on for too long.
I made sure to turn it off once it started smoking.
JK LOL

Edit: for a red build you would probably want to switch out the 7805 5v regulator with a LDO 3v regulator
which would change the 5 in the formula to 3

so many +1's. over 9000 in fact. and many thanks for the note about red

DIY Super low dropout linear driver

justinjja

0

AnthoT

0

justinjja

0

JLSE

1

justinjja

0

sesam

0

justinjja

0

rhunsulrana

0

BShanahan14rulz

0

justinjja

0

rhunsulrana

0

Online statistics

Forum statistics

Share this page