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LM317T MAXIMUM INPUT CURRENT ALLOWED.

solar boy
Prodigy 90 points

Hi Guys,

I am working on a small voltage step down circuit using the LM317T.

Input voltage : 19VDC

Input current : 2A

Desired Output voltage( from LM317T) : 13.8VDC

I am using this circuit design : 

Yesterday, i did testing with a solar panel & it burnt my filter cap( C2 ) at the output side. (probably of high current i guess).

Question is : What's the MAXIMUM INPUT CURRENT ALLOWED into the LM317T IC?

  • 0
    TI__Mastermind 24975 points

    Hello,

    So, to answer your question, the maximum output current based on the datasheet is 2.2A typical, and 1.5A minimum. Meaning, typically they should be fine at 2.2A, but occasionally the devices will not be able to tolerate more than 1.5A.

    But there are some other more important things to consider.

    Now, that's the datasheet spec, and that assumes that the device has whatever heatsink necessary to provide the maximum current. The problem that you will run into is that you are burning about 10.4W of power (2A * 5.2V dropout). If you don't have a heatsink attached then you are going to be increasing the junction temperature of the device about 240C (23.3*10.4). This is a much bigger problem and something you need to consider more highly. The maximum temperature the device can handle is 125C. Even with a heatsink it is likely to exceed 125C, so you may want to reconsider using and LDO. Possibly a buck converter may be a better choice.

    Also, if you are burning out a capacitor, you may want to make sure that this gets fixed. You want to make sure that the voltage rating of the capacitor is high enough. Also, you need to ensure that the polarity of the capacitor is correct (assuming the cap has a polarity).

    I hope this helps.

    Best,
    Michael