[sdiy] The annual I/O impedance/protection thread!

[Justin Owen]

An addendum to my last post:


1) Input: http://www.sdiy.org/juz/euro_input_01.pdf

"The back to back Zeners protect against over voltage at approx. +/-20V"

This should read +/-10V

2) Output: http://www.sdiy.org/juz/euro_output_01.pdf

the resistor value typos on this schem have now been fixed.

"The voltage follower uses a 10K/1K in the feedback loop to set the output impedance to 1K"

Since I've already had someone call b******t on this - the idea for this non-inverting config came from a post in Jan 2006

"...many designs have something like a 1K series resistor on the opamp output to limit the current. If you need a lower output impedance then you could use 100R instead, but 1K offers more protection.

A good trick, especially for critical CVs, is to put this series resistor *inside* the feedback loop so the opamp  automatically compensates for the voltage drop across the resistor (if it's a voltage follower, you will also need another larger resistor in the feedback loop from the module output back to the opamp inverting input."

Thanks,

Justin