High efficiency high output linear driver - will it work?

[dethlore]

Hey I came across this driver setup that has a very very low dropout. Their schematics show it hooked up to a lead acid battery, but based on the diagrams and specs, would this work with two 18650s in series? Could you pull up to 4A with this setup?

The IC regulator
LT1123 - Low Dropout Regulator Driver - Linear Technology

The Power Transistor
MJE1123 Datasheet pdf - PNP LOW DROPOUT TRANSISTOR 4.0 AMPERES 40 VOLTS - Motorola

 

[WonHungLow]

it should depending on the battery's used. i would probably use LiPo battery instead of LiIon for drawing this much current.
if you are planning on using this for a laser driver, it should be mentioned that it is a constant voltage regulator not constant current.
From the datasheet it should have a 0.4V drop. this is in a small TO-92 package for the regulator but the transistor is in a larger TO-220 package.
it should deliver 5V@4A as stated in the datasheet if built according to supplied schematic

 

[dethlore]

Thanks for your input Won. This should - in theory - be fine with 18650s if they have 3Ah+ and a 2C discharge rating. I hooked it up this morning and played around with the resistors. Best I could get was 1190mA, so the batteries must be crapping out.

I guess it's all a moot point if it is a voltage regulator though. bummer.

I got a couple of sample regulators and bought 20 power transistors (cause I use these things all the time for other projects anyways), so there's no skin off my back.

 

[djQUAN]

It's a constant voltage regulator. It isn't ideal for driving diodes as there doesn't seem to be an easy way to make it go constant current.