5v chip getting 14v signal

Discussion in 'The Projects Forum' started by cenee, Oct 20, 2012.

  1. cenee

    Thread Starter Member

    Apr 20, 2006
    16
    0
    Hi all,
    I am using a 7805 voltage regulator to power a chip, but an input signal going to one of its pins is coming as a +14V. How do I bring down this +input to an adequate voltage level to the chip?
    I am thinking to use a voltage divider.
    Any other ideas?
    Thanks
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,998
    745
    yep use two resistors, no diode required, use a R1=10k and R2=4k7
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,145
    3,055
    The divider is a fine way to go. Probably no reason to consider anything else.

    Some other thoughts: Are you sure the chip cannot tolerate the 14v input? Maybe it's not a problem.
    You could use a zener on the chip's input. Depending on the impedance of the source of the signal, you may or may not need a current limiting resistor to protect that zener from over-current.
    There are plenty of other ways to condition a signal, too. You can use a comparator or a schmitt trigger to square it up and send forward whatever voltage you want. Optoisolator is another choice.
     
  4. cenee

    Thread Starter Member

    Apr 20, 2006
    16
    0
    Thanks Dodgydave. Will play around with those resistors values as the voltage can also
    go down to ~12.5v. (r1=15k, R2=10K)
     
  5. cenee

    Thread Starter Member

    Apr 20, 2006
    16
    0
    Great ideas Wayneh. I will try the Zener and Opto options too. I am not sure how
    I would bias the schmitt trigger.
     
  6. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    Many chips have clamping diodes. You only need to limit the current, for instance 10 or 12 KOhms.
     
  7. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
    764
    Hope we are talking digital here.

    If the signal is analog, with a zener it would be not clamped but totally clipped.
     
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