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HELP Low dropout voltage regulator.

LaZeRz

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Hey everyone!

ok so im looking for a voltage regulator e.g lm1117 that had extremely lov voltage dropout, like under 0.8 volts that can be used to supply around 420-420ma to a 2.8v LOC diode.... The reason im looking for a voltage requlator like this is because i would prefer to use a 22600 in a hotlight then two 3.6v cr123a's...... The 22600 fits perfectly and hold double the ma so its a win sin situation if i can find such a chip :D

Thanks in advance.....
 

mb300sd

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Heres the distributor listing for it, its very easy to wire up the circuit with a couple resistors, post back if you need a diagram.

LM1117 - 800mA Low-Dropout Linear Regulator

I'd suggest digikey in the US, but I'm not sure if they ship to Australia. You can try ordering a free sample from National directly too, say its for a school project and they'll probably send one.
 

LaZeRz

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I though a lm1117 couldnt supply 430ma on a singlie li-ion i guess im proven wrong :D
im ordering a couple of lm1117 drivers from jib il ask him about voltage but im wondering are there any other chips like a lm1117 but more efficient?
 

rhd

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I have a running theory (that I think is correct), which is as follows:

- The DDL circuit with 1.25V VREF will never give you a dropout below 1.25V, because the current is always passing across that resistor, and the whole system works based on maintaining that 1.25V drop.

- The lowest dropout IC I've seen available on Digikey specifies a ~0.3V dropout (I'm sure there are some lower). But even then, and that's a crazy 5-pin IC, you're still going to have to add that 0.3V to your 1.25V drop across the resistor, for ~1.6V total drop.

In other words, 4V battery - 1.6V = 2.4V, and thats when fully charged.
This is why I aborted my hunt for an IC that could run a LOC from a single cell based on a linear driver circuit design.

Apologies if bubbles have been bursted. ;)
 

LaZeRz

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Thats ok :D its just cause lazereer build a LOC running from a single li-ion based on a chip that he found in a stereo or something :D
 

rhd

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I think your best bet is to grab a single lithium ion cell, wire it to a test load direct, and measure the current. If it's not above what your LOC can handle, add a couple caps to the system, and direct-drive. This would probably only work for a 10440. I would imagine the 14500s can do closer to 1A of current. Too much.
 
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Maby just forget the driver all toghther and put a current limiting resistor in there :thinking:
 

LaZeRz

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Well i dont really thing just a resistor would work very good and just using 1 batt and wiring it up to a testload (which i dont have) and i dont got a DMM nor do i have a 10440 battery nor do i have any diodes.... lol i dont think i can go Kipkay just yet :D
 




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