Gah, failed LM1117 qgain! Help?

• Apr 16, 2011

• #1

Wolfman29

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Hey peeps.

I was trying to make an LM1117 based driver for my PHR... but it won't work!

Here is an exact replica of the soldering and PCB I made for it.

When I plug it into roughly 8V of input, on my testload, I get a fluctuation between 3.2A and 800mA-1A, and then it drops to zero, repeat.

It *should* be giving me roughly 113mA... but it's not! What's wrong here?!

 

• Apr 16, 2011

• #2

MA257

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your drawings just a tad bit confusing:thinking:

if you could possibly label where C1, C2, R1, and R2 are i could help

 

• Apr 16, 2011

• #3

bluuray

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i think your supposed to be using the negative when using a test load..
not sure though

 

• Apr 16, 2011

• #4

Eudaimonium

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You're connecting the diode output from the wrong side of the resistor chain. It should go from ADJ side, not OUT side.

Just make your OUT+ (assuming it's diode positive) directly on ADJ. It'll magically work.

Don't mention it

 

• Apr 16, 2011

• #5

bluuray

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oh ya lol just saw that..
+ is from the ADJ pin.

 

• Apr 16, 2011

• #6

Wolfman29

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Oh. Awesome. Thanks everyone!

 

• Apr 17, 2011

• #7

Wolfman29

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Okay, so that didn't work, unfortunately. I did the same thing, except connected the adj and out right at the pins, and then stuck the resistor chain after it, and I was getting a constant current of around 360mA... I need 107mA or so from the 11Ohm resistor.... What's wrong, damnit!?!

 

• Apr 17, 2011

• #8

Toke

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Well, don't connect out and adj right at the pins.

You should connect them after the resistors, and then connect the load at the adj pin.

ETA: It looks like you have ground/- connected to the regulator +in, that would make a short circuit.
You don't need ground for the regulator.

 

• Apr 17, 2011

• #9

bluuray

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ya just run the load neg to battery neg

 

• Apr 17, 2011

• #10

Wolfman29

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What about the cap then? The caps need to go to the GND, don't they? And thanks - will try that after I take my brother to the ER :\

 

• Apr 17, 2011

• #11

bluuray

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just connect them like this.. :I
Laser driver - It can be done

 

• Apr 17, 2011

• #12

Wolfman29

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I feel like an idiot. Know why? Because I have seen that before, and I even know that the left pin is adj. I just always thought that I connect out to out =p

 

• Apr 17, 2011

• #13

Wolfman29

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But, it works now! Woot! Just working on making it smaller now (with a file) so I can fit it in the pill.