Hi all,

I have a project where a vacuum pump outputs a 22V signal indicating
whether it is working or not.  If it malfunctions (0V) I need to stop the
process.  The signal goes into a datalogger which is controlling everything
(I wasn't allowed to use a PIC to set this up).  The datalogger needs a 5V
signal, but I would like the pump to be electrically isolated because it's
very expensive and a huge pain to fix/replace.  The way I decided to do
this (one-time project) was use a 24V-5V DC/DC converter (DCP022405P).  I
have a 2.2k resistor that goes from the converter's output to the digital
input (it only tolerates very low current) and also a 500 ohm resistor that
goes from the output to a LED for monitoring the status.  The inputs of the
DC/DC converter come straight from the vacuum pump (the pump signal is
current limited to about 50 mA).

This worked great for about a month until someone unplugged the connections
to move the setup around.  Then it wouldn't work -- somehow the chip just
died.  I popped in another chip and it worked fine until the power went out
last night.  When the power came back on the chip was fried again, no
unplugging of anything.  I figured maybe some ESD the first time, but now
I'm not sure, maybe the pump output goes screwy at times (it really
shouldn't though).  Is there something I should be putting in between the
pump output and the DC/DC converter input to protect it?  Some kind of
resistor or RC combo?

Thanks,
Mark


PS I thought about using an optoisolator and a 5V VCC, but the main power
for everything is 12V.  So I would need a voltage regulator or zener to
goto 5V for this IC.  Plus I had never used a DC/DC converter so I figured
this was a good opportunity to play with one.

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