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Is cycling a switching power supply on/off a problem

Discussion in 'Power Electronics' started by JacobT, Feb 27, 2013.

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  1. JacobT

    JacobT

    3
    0
    Feb 27, 2013
    Hi guys
    I'm trying to piece together a temperature controlled system using a PID and a TEC.

    Now my original idea was to use one switching power supply to power the PID and the same to power the TEC, and control power to the TEC via a SSR (which in turn is controlled by the PID).

    However, the SSR I have is for AC output, so it will not work with the 12V DC i'm getting from the power supply.

    An alternative is to use a separate power supply for the PID and then have the SSR cycle the 12V switching power supply on/off as needed.

    The question is, will the expected fairly rapid on/off cycling potentially damage the switching power supply?

    Hope that makes sense... I'm quite the novice..

    thanks
    Jacob
     
  2. pwdixon

    pwdixon

    52
    0
    Oct 14, 2012
    Just use a mosfet to switch the TEC current and let the power supply be on all the time. It'll be way cheaper than the SSR in any case.
     
  3. JacobT

    JacobT

    3
    0
    Feb 27, 2013
    Thanks for the quick reply. I've gotten a mosfet and that does seem to be a better solution.. only I have a small "secondary" problem. The PID I have seems to have the positive "terminal" constantly hot and then "switch" ground (hope that makes sense) the problem is that I have a constant +10V from the positive terminal, so the mosfet is constantly "on".

    Any easy way to fix this?

    Thanks, I hope my mumbo jumbo makes sense :rolleyes:

    -Jacob
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    11,530
    2,656
    Nov 17, 2011
    You probably have an NMOS FET.
    Use a PMOS FET
     
  5. pwdixon

    pwdixon

    52
    0
    Oct 14, 2012
    Are you trying to switch the high voltage side or the low voltage side?

    If you have an N channel FET you could switch the low voltage side but you might want to invert your drive signal if On and Off are interchanged.
     
  6. JacobT

    JacobT

    3
    0
    Feb 27, 2013
    Hmm Thanks, I'll look into this, does it work like the NMOS only I connect the positive rail to the source? and then connect my "negative/ground" terminal on the PID to the Gate?

    Thanks again.
    -Jacob
     
  7. pwdixon

    pwdixon

    52
    0
    Oct 14, 2012
    Can you draw a picture I can't tell what you circuit looks like.
     
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