H11L1 limits

Discussion in 'General Electronics Chat' started by adwina2, Oct 26, 2015.

  1. adwina2

    Thread Starter New Member

    Jul 14, 2015
    18
    2
    Hello all,

    I have a pretty basic question concerning Fairchild's H11L1. I am using it as isolation and also to step up a switching voltage from 5V to 12V or 24V for a drive circuit. The output of the H11L1 will only be turning on an NPN BJT(2N3904) which should require less than a milliamp and a 10K resistor to ground which will only pull a few milliamps. Under "Safety and Insulation Ratings" in the datasheet it claims Ps is 800mW. But, under "Maximum Ratings" in the datasheet it claims the output can only range from 0-16V. Since I am only drawing a few milliamps at the output, can I use 24V for Vcc as long as I stay below 800mW? Or does the higher potential on the collector cause problems over time?

    Thanks in advance!
     
  2. #12

    Expert

    Nov 30, 2010
    16,298
    6,808
    I'm afraid you have a problem. The "Absolute Maximums" don't go above 16 volts.
    You have to obey each limitation individually and collectively, so you thought you had an, "out" but you don't.

    ps, thanks for providing the datasheet.
    pps, There are probably ways to do this just as well with different parts.
     
    adwina2 likes this.
  3. adwina2

    Thread Starter New Member

    Jul 14, 2015
    18
    2
    Thanks for the response. My original prototype uses 12V at this stage and it works fine, so I can keep it with an extra amplifying stage, I was just trying to clean up the flow a little. Is the issue with the higher voltage in the "off" state, where the higher potential might start passing the junction, or is it because this is an IC and becomes a blackbox where you just have to obey the rules?

    Also, if anybody has any recommendations for better optos I am open to suggestion for future projects. I have only used H11L1 and H11F1 depending on application and I am sure there are better options out there. I mostly use them for digital isolation from a micro or for analog isolation in 0-12V system.
     
  4. #12

    Expert

    Nov 30, 2010
    16,298
    6,808
    More the black box thing. It is actually a little annoying to see you talk about the collector in the Schmidt trigger because you have no evidence it exists. These chips are usually made with mosfets, so your words make me want to correct you...but I try to suppress the urge unless your words are involved in an important part of the question. (Some people can't restrain themselves from finding every tiny mistake and writing a book about it.)

    Now, be clear about your request. Do you need a higher voltage opto-isolator? Does it need to be a Schmidt? Anything special about the speed or the output current or whether it inverts the signal? etc.
     
  5. adwina2

    Thread Starter New Member

    Jul 14, 2015
    18
    2
    I appreciate the restraint, but I only used the word 'collector' because the datasheet calls pin 6 Vcc.

    As for the updated opto, I was just looking to see if there is another family similar to the H11 that incorporates both analog and digital isolation. I like the schmidt output of the H11L1, but I have more trouble with the H11F1 because you have to offset the input around a volt(if you go to zero volts) and the linear region is fairly small. I think I will let this question wait until I need it for a specific application so I can provide more details, since I already made a circuit around the H11F1 for this application. I realized I am asking too general of a question for this forum.

    Thanks again for your responses!
     
  6. #12

    Expert

    Nov 30, 2010
    16,298
    6,808
    You're right. The idea of analog isolation and offset has me chasing my tail without a circuit to imagine it in.
     
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