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LM1117 Driver Build Questions

Fretwrecker94

Fretwrecker94

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Hi I've been noticing the success rate of many LM1117 drivers recently. I am thinking of building a few for my use. Is there any schematic someone can provide me of an LM1117 current regulator? I've looked all around the forum and can't seem to find one. I understand it's pin-out is identical to the LM317, but I've heard you absolutely need 2 10uf Ceramic Caps.

Any help would be appreciated. If this seems to be a redundant thread and/or someone provides me with a link to a helpful thread, I will most certainly delete this for bandwidth's sake :)
 





foulmist

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10uF are by datasheet..
they are there for stability and ripple control

here is a simple diagram which I drew in photoshop because I don't like paint :D

attachment.php
 

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rhd

rhd

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foulmist said:
10uF are by datasheet..
they are there for stability and ripple control

here is a simple diagram which I drew in photoshop because I don't like paint :D

attachment.php
Click to expand...

I think you'll find that the < 1.45 VDrop figure doesn't hold up. The resistor itself will drop 1.25V, and it's not the case that the IC only drops 0.2 V.
 
Benm

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You should add up those drop voltages indeed, resulting in something around 2.7 volts for the whole thing.

The output cap doesnt have to be 10 uF really, using a good quality 100 nF ceramic cap will do fine. The input one can be electrolytic if you like.
 
mpwn

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may i ask what is the advantage of this compared to a LM317?
 
Blord

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The LM1117 has less drop voltage than the LM317. Therefore you have more choices in combination of batteries to power the laser.
 
mpwn

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what added combination are available like e.g 3xAA?
 
mpwn

mpwn

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ahh kk , lol i thought you were trying to say idono :D
 
foulmist

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rhd said:
I think you'll find that the < 1.45 VDrop figure doesn't hold up. The resistor itself will drop 1.25V, and it's not the case that the IC only drops 0.2 V.
Click to expand...

Benm said:
You should add up those drop voltages indeed, resulting in something around 2.7 volts for the whole thing.

The output cap doesnt have to be 10 uF really, using a good quality 100 nF ceramic cap will do fine. The input one can be electrolytic if you like.
Click to expand...

yes you are both right, i should change the picture :D
 
kiyoukan

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so whats so good about this driver?
in this setup the v drop is over 1.25V right?
im confused as why these sold so well?
 
rhd

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kiyoukan said:
so whats so good about this driver?
in this setup the v drop is over 1.25V right?
im confused as why these sold so well?
Click to expand...

It's better than an LM317... that's about it.

Why someone would use an LM1117 now, when we've got so much data on the reliability of 1084 and 1085 drivers, is beyond me. Availability and cost perhaps?
 
kiyoukan

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even still i got a linear driver that has a vdrop at 2a of around 0.55v
and as soon as the new batch of chips gets here will have slope.
 
Benm

Benm

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rhd said:
It's better than an LM317... that's about it.

Why someone would use an LM1117 now, when we've got so much data on the reliability of 1084 and 1085 drivers, is beyond me. Availability and cost perhaps?
Click to expand...

Probably, although i dont see a big advantage of a lm1048 over the 1117 unless you need currents over 800 mA. I guess people stick to the 317 since it was part of the first diy drivers presented here. Sadly its a poor choice for that function with todays components being available. The upside is you can just drop in a 1117 or 1084 when the 317 doesnt cut it any longer :)
 
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