Cant be 37v out with 38v input.

drop-out voltage can reach 1v in very hot / low load conditions.

 

Only using the input AC as 12Vac,0V and you will be get about 17Vdc.
B 10K(R2) change to the same value with R1 use the fixed resistor, R2=220 ohms.
Make sure again the pins should be connecting correctly.


LM317 Datasheet.

 

Hi

I think the LM317 is damaged. Cant be 37v out with 38v input.
Should only be about 5mA thru R2 (ADJ) resistor

Hi, You are right LM317 is damaged. I replaced a new LM317 and checked the continuity, it was ok. But circuit damaged it again.
Till now i have connected SIX LM317 but all got damaged after powering on.
sometimes adjuster and Vout short and sometimes vin and vout and once i got all three pins shot.

Please suggest.

 

Hi, i checked Lm317 its short but why LM317 short all the time. I replaced a new LM317 and checked the continuity, it was ok. But circuit damaged it again.
Till now i have connected SIX LM317 but all got damaged after powering on.
sometimes adjuster and Vout short and sometimes vin and vout and once i got all three pins shot.

Please suggest.

 

Throw that stupid circuit through the window! You are insisting on the same error and doing so is not going to change anything. Burning ten more will not make you wiser.

Instead of a schematic draw a mimic diagram showing the physical disposition of parts. You could connect (solder) things on the air for quick check so you quickly disconnect things if you are not getting the right results.

Have you checked that the regulator can take that high input?

Is the transformer output the value you actually expect? Measuring AC instead of DC or viceversa creates sure havoc.

 

Hi, i checked Lm317 its short but why LM317 short all the time. I replaced a new LM317 and checked the continuity, it was ok. But circuit damaged it again.
Till now i have connected SIX LM317 but all got damaged after powering on.
sometimes adjuster and Vout short and sometimes vin and vout and once i got all three pins shot.

Please suggest.

Hello,

The LM317 can take up to a 40v input output differential voltage. Make sure it is not more than that, even the peaks. In fact, since you had so much trouble already you should start with a very low input like 10v and get it working first.

There is either something very basic wrong or perhaps you got some counterfeit LM317's. Use a much lower input voltage to test this, then raise later once you get it working and see if it continues to work. Counterfeit IC's typically have a lower rating than the real ones so it may work at a lower voltage.

As someone else said, get rid of the pot and instead use a 220 ohm resistor and apply 10v to the input. You should get something around 2.5v as the output assuming your upper resistor is still 220 ohms, which BTW, you should check with an ohm meter to make sure it is the right value.

If you do this little test first you will get some results assuming there is no bad connection or bad IC.

These circuits are very simple, we build them all the time. Just another one yesterday in fact, only with a higher power version of the LM317 which is the LT1083 good for 7 amps. Dont let this circuit get you down. There is something beyond your control wrong right now but doing a few little tests will tell us what is wrong. Whatever you do, dont connect the same circuit again as it will probably just blow more parts.

 

Hi

I think the LM317 is damaged. Cant be 37v out with 38v input.
Should only be about 5mA thru R2 (ADJ) resistor

The current through R2 is (Vout-1.25 )/R2
If Vout= 37V then P in R2 = 35.75^2/ R2 ~ 0.13 W, which might be too much for the pot.

 

Are you using a proper pot not a trim pot?

 

What's the power dissipation over the pit at 37vout?

The schematic looks okay. Input voltage is a bit high for the LM317. Maybe try LM317HV. Capacitor is overheating???? Rectifiers wired correctly?
How much voltage did you actually need out?

 

Hi, You are right LM317 is damaged. I replaced a new LM317 and checked the continuity, it was ok. But circuit damaged it again.
Till now i have connected SIX LM317 but all got damaged after powering on.
sometimes adjuster and Vout short and sometimes vin and vout and once i got all three pins shot.

Please suggest.

Hi

The basic LM317 circuit is pretty simple. As another poster stated, maybe the LM317's are counterfeit or otherwise no good..
Post the schematic and take a photo of your wired circuit and upload it so we can review it.

I wouldn't test anymore circuits until we review it.

Where did you buy the LM317's?

 

Lets have some pictures of your work and wiring, maybe you made a mistake...

 

The schematic looks okay. Input voltage is a bit high for the LM317. Maybe try LM317HV. Capacitor is overheating???? Rectifiers wired correctly?
How much voltage did you actually need out?

No over heating, caps are all ok and rectifiers are wired correctly.

 

There is no problem with the schematic, so the problem must be in the way you have wired up the circuit. Without better information from you, the advice here probably will not solve the problem. A sketch of your physical connections would help; so would clear photos.

What is the desired output voltage range?
What is the desired output current range?

As suggested, replace the pot with a fixed resistor, calculate the output voltage, and debug the circuit until it is correct. Only after it is regulating correctly should you go back to the pot.

ak

 

If every attempt ends with the destruction of the regulator then there is something functionally wrong with the design implementation. We need to see this please. Yeah definitely need some pictures please

EDIT, why did you use a 470uF instead of a 47uF for Co? I only ask because I am concerned as to the pathway the capacitor has to discharge which could cause problems.

 

Please find attached pictures of circuit on breadboard. Images are bit heavy (4K)

 

Do you have an insulator between the LM317 and the heat sink?

 

Looks like your output capacitor is in series with ground rather than parallel (until you put a small dummy load on the output i.e. LED or Resistor/both) and it's discharging either through the regulator or through the pot to ground. Or the path of least resistance for Vo would always be through your adj resistors (R1 looks rated the pot won't be). And put your LEDs on the output side of the regulator and you should be using the protection diodes as described in the datasheet.

 

Do you have an insulator between the LM317 and the heat sink?

An insulator isn't necessary if the heat sink is not touching anything else, which it does not appear to be.

 

An insulator isn't necessary if the heat sink is not touching anything else, which it does not appear to be.

well...it shouldn't...but...

 

It seems as if there is a short across the regulator from input to output. That would put 38v across the program resistors (and pot).