View Full Version : LM317 @ 3.3v problem

06-14-2009, 05:48 PM
Hello all !
Please take a look:


I made this circuit with r1=240 ohm and r2=390 ohm . I made it with correct pin numbers (1-input,2-Vadj,3-output) ,not as per the diagram
The unloaded output is 3.3v . Good. The bad part is that as soon as i connect *any* resistance (i tried 470ohm,4k7 etc)across o/p and ground,the voltage drops to about 1 volt

I'm using a 9v lead acid (fully charged) and there are no problems in breadboard/wiring (i checked many many times !)

Is there anything i might be missing ?
And can anyone tell me any other way to get 3.3v (@100mA) from a 9v supply? (other than using diodes to drop out the voltage or hard to find LDOs)

06-14-2009, 08:08 PM
Why not try 78L33 or equivalent.

06-14-2009, 08:19 PM
try adding a capacitors across both the input and output sections.
Also , the problem might be with the LM317 itself. I've had similar problems before with 78xx series , and the defect turned out to be in the regulator itself.

06-14-2009, 10:21 PM
Hey,thanx for the replies !

@Vikas - I have already tried finding 78l33 but couldn't ! (I live in chandigarh)


I tried adding caps.....no effect

But am going to buy new LM317 so will post back.

Again,thanx a lot guys! :D


06-15-2009, 12:49 AM
Hi I saw ur circuit,
I saw the data sheet and as per the data sheet the voltage diffrence btw out and adj is 1.25V . as per the mathematics ur resistor value seems wrong to me. the ratio of r2:r1 should be 6:5 as 1.25(1+1.2)= 3.3 V. So check your circuit again.......


06-18-2009, 01:03 PM
Hey guys!
Thanx for the replies !!

Just got new LM317s

THEY WORK FINE with this circuit !
I'm getting 3.3v @100mA (should get more current;haven't tried that yet)

1.25(1+1.2)=1.25*2.2 =2.75 (not 3.3)

and my circuit is running fine with new LMs !