Values of LM317 regulator that will generate Vout of 5V, 3.3V, 2.5V or 1.2V

Hi All,
can anyone tell me the values of R1 and R2 for LM317 regulator to generate Vout 5V, 3.3V and 2.5V and 1.2V.

Vin is 9V @ 500mA


Thanks,
Gold_kiss

lm317t 3.3v

I fear you're using the Fairchild datasheet, which doesn't contain the formulas. This datasheet from National Semiconductor contains everything you need. Don't be lazy ....
**broken link removed**


Mik

how to use lm317

Formula for calculating :

U out = 1.25*(1+R2/R1)

If you choose R1 = 1k

R2 ( 5v) = 3k
R2 (3.3v) = 1.65k
R2 (2.5V) = 1k
.............................................

Bojan

lm317 5v

You should try to use a high value for the resistors so that they would not incur much power....

lm317t 3.3 v output circuit

Thanks,
Can i generate 1.2V using LM317? if yes how?

Thanks,
Gold_kiss

lm317 example

In the datasheet 1.2 V , is the lowest value that LM317 can output, but practically it does not happen, but is you wanna tri put R1=R2 and Radj = 0, for this kind of voltage use a low-drop regulator.

lm317 formula

In my book "Excel by Example : A Microsoft Excel Cookbook for Electronics Engineers", Newnes, ISBN 0750677562 I devote a whole chapter in building a model for the LM317 in Excel.

The example includes the resistor calculation (using standard resistor values) using the Goal Seek feature of Excel, thermal analysis, and input capacitor selection when driving it from a rectified AC source. Once created, you can reuse the model every time you create a dc power supply with the LM317.

I also cover similar topics for the TL431 and LP2951 where resistor ratios need to be calculated.


I hope I didn't offend anyone by this thinly veiled advertisement! :roll:


-Aubrey Kagan

lm317 3.3

for current through resistor is 5mA:

5V output : R1 = 240R, R2 = 750R;

3V3 output: R1 = 240R, R2 = 410R;

2V5 output: R1 = 240R, R2 = 240R;

1V8 output: R1 = 240R, R2 = 110R;

best regards

gold_kiss said:

Hi All,
can anyone tell me the values of R1 and R2 for LM317 regulator to generate Vout 5V, 3.3V and 2.5V and 1.2V.

Vin is 9V @ 500mA


Thanks,
Gold_kiss

Click to expand...

3.3v lm317

By the way, can you tell me some outstanding differences between LM317T and LM317HVK

Thank you in advance!

lm317 3v3

LM317HV is a high voltage version of LM317, I can't remember the exact figure, I think it is having 10volts higher rating compared to LM317. Read the datasheet for futher details.

how to use a lm317

if you want to design a 1.2 V output, you may try to design yourself a circuit, or you could try other manufacturers like TI or maxim-ic. but i doubt you can create that low of a voltage because of the voltage drop of diodes are around 0.7 volts, and to properly bias a diode you need to raise the voltage higer than the bias voltage,...

lm317 3.3 v

Here are good html calculator for LM317
https://www.muzique.com/schem/lm317.htm
I use this...

here are 2 other calculators
**broken link removed**
**broken link removed**

Good luck

lm317t 3.3 v

hi,
Ithink the fixed value resistors r not suitable here because they can vary little bit.
but here you can use variable resistors to set your required voltage value that is the best way

bye

lm317 how to use

I use 2 fixed resistors in serial connection, to find the specific value.
better and cheaper

lm317 3.3v circuit

you can lookfor any datasheet ( of course not all but many ) you want at this site :
https://www.alldatasheet.com/
hope this be useful

note : replace '**' in the h**p with 'tt'

lm317 3.3v regulator

From 9V power supply, you can use LM317 to create 5V down to 2V with no problem, but lower than 1.5V is problem as it is about the reference voltage.

The LM317 datasheet from National semi provides most complete info, including how to create the voltage from 0V upward by a LM317 with a minor addition to the circuit - the - rail and a 1.2V reference which is used to compensate the LM317 internal reference voltage.

Feedback if you do not have a - rail, as you need to create it.

nguyennam

Added after 8 minutes:

Regarding the datasheets, my experience is: trying to find out the ones from the manufacturers' website, especially the original inventor-manufacturer, for example LMxxxx ICs from Nationnal Semiconductor website, Txxxxx from TI, Mxxxx from ONsemi, Freescal (formerly Motorola semiconductors), etc, ...

The datasheets from manufacturers are always free, and usually contain the most fully set of info like technical characteristics, application hints, circuit examples, ... while the datasheets from any other sources, especially free ones, only contain the most essential info as technical characteristics.

It is also easy to find out the datasheets from manufacturers' website, just "google" the keyword and then look for the link from manufacturer.

Only looking for the datasheets from any free sources, like datasheetarchive.com in the worst situation.

Hope that may help.

nguyennam

Re: LM317

hi,

The perfect equation for LM317 is

Vo = Vref(1+R2/R1) + Iadj*R2

where Vref=1.25

But what about Iadj*R2 Term??

How to calculate Iadj in this???


Thanks,
rushabh

Re: LM317

How to calculate Iadj in this???

Click to expand...

You can't calculate it, read it from the datasheet. But it's affected by temperature and load variations. So basically, keep R2 sufficient low that these variations can be ignored.

Re: LM317

Hi fvm,
Can u please tell me what is the value of R1 and R2 in LM317 circuit for 5V Input

Re: LM317

use

LM317 Voltage Calculator - Electric Circuit
or


Alex