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Component reliability

  1. Dec 4, 2014 #1
    I have very little experience with electronics so I have come here to hopefully gain your insight into an issue that is currently being discuss amongst people who seem to have no clear answers.

    The circuit I am interested in utilizes a 9V battery run through a LM334Z current regulator, with a 33ohm resistor to limit the output of the device to 2.0mA .
    Can and do these components fail and what is the probability of failure considering only a 9V battery as a power source? Are there better components to use?
    Any empirical references to component failure would also be appreciated.
    Hopefully that will be enough to get the subject off the ground.
    Thank you.
  2. jcsd
  3. Dec 5, 2014 #2


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    Gold Member

    Component reliability is expessed by MTBF (mean time between failures) and/or FIT (failures in time). You can use google to understand MTBF and ask furthur questions.
    It is a pretty deep subject, actually.

    Here is the reliabilty page for the LM334Z

    It has a 50% chance of failure in 66 9.122* 107
    hours. But I don't know about the space between 66 and 9.
    Or, 11% failures in 10**9 hours.

    http://focus.ti.com/quality/docs/singlesearchresults.tsp?&templateId=5909&navigationId=11213&appType=folders&searchType=orderableOption&partialSearch=false&mtbfType=true&orderablePartNumber=LM334Z/NOPB [Broken]

    Basically you use the MTBF for all components to determine the circuit failure rate.
    Last edited by a moderator: May 7, 2017
  4. Dec 5, 2014 #3


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    Staff: Mentor

    We would need to know more about the problem you're trying to solve to answer that question sensibly. What's the purpose of the circuit? What's the operating environment? How long must it function? How many units are you building?
  5. Dec 5, 2014 #4
    This is already a good start with the MTBF link. Thank you, I appreciate a forum with serious thinkers, it's just what I was looking for.
    To be clear I am not building these devices, my hope is to better inform the community who is, sort of a public service in the interest of safety. The community I refer to is the DIY tDCS community they are self treating for a wide range of mental issues by applying a current of 2.0mA through electrodes places on various parts of the cranium, there is lots of empirical medical data on its effectiveness, I do not wish to have any part in the medical recommendation of treatment. These people are going to do this regardless, because clinical application is expensive and not available in most places.
    My interest and purpose here on this forum is for experts in how electricity works to just take a look and see what is the safest way these devices could be configured to protect a user. I believe these devices to be fairly harmless when limited to 2.0mA. So that's the situation, what is the safest way to limit a 9V battery to a maximum output of 2.0mA? Are CRD a better choice.
    I humbly ask the electronically enlightened people for there input.
    Thank you.
  6. Dec 5, 2014 #5


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    Staff: Mentor

    No, sorry. We do not discuss dangerous activities here on the PF. Please refer to safety standard UL 544 for medical equipment design. Thread is closed.
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