Is cycling a switching power supply on/off a problem

[JacobT]

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

 

[pwdixon]

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.

 

[JacobT]

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.

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

-Jacob

 

[Harald Kapp]

You probably have an NMOS FET.
Use a PMOS FET

 

[pwdixon]

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.

 

[JacobT]

You probably have an NMOS FET.
Use a PMOS FET

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

 

[pwdixon]

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

Can you draw a picture I can't tell what you circuit looks like.