Problem with voltage regulator

[Tesladude]

So I need to use this LM117t 3.3v voltage regulator and I asumed the pins were the same as most regulators where you have in/ground/ and out. But it is not working that way, does anyone know the in and outs of this regulator or have an alternative?

 

[davenn]

hey t-dude

not its not ...
its never safe to assume anythig in electronics... always test, measure and in this case check the datasheet

LM117T-3.3

page 3 gives the pin out configuration for the various package forms

the output as you will see is the centre pin

hope that's helpful


cheers
Dave

 

[meBigGuy]

lm117 is an adjustable regulator. It works by generating an output voltage such that the voltage at the reference input (what was ground in a fixed output regulator) reaches 1.25V. So it you have R1/R2 divider with equal values the output will go to 2.5V producing 1.25V at the "center" pin. If you connect the output to the reference input you will get 1.25V.

The datasheet that davenn linked to is for an LM1117 (different number, 3 1's) that is a family of fixed output regulators.

 

[davenn]

that's interesting as it was also saying 117 at that page

LM1117T-3.3 - LM1117 3.3V Low Drop-Out Voltage Regulator
Technical Information - National Semiconductor LM117T Datasheet

I wonder if the TD typoed and was meant to say LM1117t-3.3 and not the 117t-3.3 that he did ?
cuz he was pretty specific with the rest of the info. he wasnt referring to setting up an adj regulator huh

so I will stick with the info I gave till TD reports back in

 

[Tesladude]

MY BAD!

Lm1117t!

The datasheet also says ground output input and I just tried that and i am getting the exact same output as I have input (9v)

 

[davenn]

show me a pic of you circuit digram and also a pic of your actual construction
to see if you boo boo'ed :)

that V-reg is different pinned to the LM78xx series fixed regulators where the GND pin is the centre pin

Dave

 

[Tesladude]

those are the 2 ten caps shown in datasheet circuit

 

[davenn]

Hi TD

through the dark blurryness it looks ok
assuming you have put the electro caps in the correct way around ?

you didnt have this connected incorrectly originally did you ?
your opening comment

So I need to use this LM117t 3.3v voltage regulator and I asumed the pins were the same as most regulators where you have in/ground/ and out

indicates you probably did. you may have damaged the regulator, do you have another one to try ?

Dave