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LM317A: Is this part is alternate for LT317?

Venkatesh P17
Intellectual 895 points
Part Number: LM317A
Other Parts Discussed in Thread: LM317

Hi TI Team,

1) Can I consider LM317 to the alternate for LT317?

2) I downloaded the spice model of LM317 and ran the simulation but I found the current was not equal to the simulation of LT317 [Please refer to the attached image], why this difference occurs?

3) If I choose SMD [SOT-223] Package, is it manageable to have without heat sink? while I configure it to 500mA using 2.5-ohm resistor?

The circuit basic can understand from this link: 

[http://www.bristolwatch.com/ccs/LM317.htm#:~:text=Also%20see%20LM317%20High%20Power,used%20as%20a%20current%20limiter.]

[https://theparanoidtroll.com/2011/01/05/constant-current-sourceload-lm317/]

Thanks and regards,

Venkatesh P

  • 0
    TI__Mastermind 44790 points

    Hi Venkatesh,

    Here are the answers to your questions:

    1) Can I consider LM317 to the alternate for LT317? *Yes. 

    2) I downloaded the spice model of LM317 and ran the simulation but I found the current was not equal to the simulation of LT317 [Please refer to the attached image], why this difference occurs? *I think you might see the same thing if you import the LM317 model in LT spice. The issue is that the model simply uses 0V for the ADJ pin and I believe your use of the -12V at VOUT is making the error. If you compare the actual devices on an EVM you would get closer results. 

    3) If I choose SMD [SOT-223] Package, is it manageable to have without heat sink? while I configure it to 500mA using 2.5-ohm resistor? *Any xx317 has a Darlington output stage so there is a fixed drop-out of ~1.4V  So with a 500mA current, this would be dissipating 700mW of power. The SOT-223 package has a TJA of 66.8C/W  so your thermal rise would be ~TJ=TA+PowerDissipated*TJA or ~46.8C above ambient. 

  • 0 in reply to JCHK
    Intellectual 895 points

    Hi JCHK,

    Thanks for the quick response.

    I also imported thIs spice model to LTspice but I didn't get the result but got an error [Please refer to the attached image].

    Yes, you are correct, -12V is a problem here. So I modified it somewhat and it working fine in simulation.

    But my doubt is whether the realtime circuit will work with -12V?

    Thanks and regards,

    Venkatesh P

  • 0 in reply to Venkatesh P17
    TI__Mastermind 44790 points

    Hi Venkatesh,

    Yes. I have seen other issues with this model it could probably use a refresh.

    The actual device can float so it only tries to regulate VOUT 1.25V above whatever potential is on the ADJ pin. As long as you are not violating the Absolute maximum ratings of the device you will be fine. If you want to confirm, I would encourage you to get in touch with your local sales to see if they can assist with providing an EVM.

    I hope this helps.