Looking for a parameter of TL431

Discussion in 'General Electronics Chat' started by praondevou, Oct 17, 2011.

  1. praondevou

    Thread Starter AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    I'm looking for a parameter telling me the maximum allowable voltage on the reference input of the TL431. It only gives me the max. input current. There is no reference voltage parameter under Absolute Max Ratings.

    What if I wanted to use it as a voltage comparator where the reference voltage will exceed 2.5V, e.g. 15V? It should work, question is, how long....

    I attached a diagram. Ignore the transistor type and the absolute resistor values, I didn't even check the transistors parameters... it's only about the max voltage on the ref input.

    Any ideas?

    Thanks
     
    • 431.PNG
      431.PNG
      File size:
      24.4 KB
      Views:
      22
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    In the TI datasheet heading, it says:
    Absolute max for the cathode voltage is 37.
    http://www.ti.com/lit/ds/symlink/tl431.pdf
    I don't know who's datasheet you're looking at.
     
  3. praondevou

    Thread Starter AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    Mmh, yes it says adjustable "output" voltage. The way it is normally used the reference voltage will not go higher than 2.5V, because this is where it begins to conduct, and the 2 resistor divider is normally connected to the output voltage.
    I'm planning to put a resistor divider that will apply a voltage much higher than 2.5V at the ref input. The 431 will conduct but the ref input voltage will not decrease because the divider is connected to the input voltage. I'm not worried about the cathode voltage parameter.

    edit: btw, the TI datasheet has an internal diagram included... thanks
     
    Last edited: Oct 17, 2011
  4. praondevou

    Thread Starter AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    The TI datasheet has an application called voltage monitor (figure 26) that is very similar to what I'm doing. In my case it will be an over and under voltage lockout...
    I guess the REF input's max voltage rating is supposed to be the same as for the cathode, even though it doesn't mention it. But if they put it in their datasheet it's obviously allowed.

    Thanks again
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I had to run out for a bit - looks like you found the info you were looking for. That TI datasheet is pretty good - lots of example circuits.
     
  6. praondevou

    Thread Starter AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    Yep, already saved on my HDD. ;)
     
Loading...