suggest a varistor

Hi,

I'm hoping someone with a knowlege of developing circuits for automotive applications can help me.

I'm developing a simple circuit to go in a car which has a number of inputs that tie into the signals from the door locks. I want to protect the ICs inside from static and i want to use a MOV (metal oxide varistor) in parallel with the input signal line but i'm unsure of how to select the right one. The signals are 0.3 - 11.7V logic and interface directly with a CMOS IC.

I hope someone can throw a bit of light on this.

I was also wondering - i opted for CMOS because of the low quiescent current, and also its high supply voltage rating, but is it OK to use CMOS in cars? Are there any issues i should be aware of?

Thanks,

John.

I've designed several circuits that interface with door lock actuators.  You can never have too much protection on an input, but it sounds like you are over complicating things a bit. 

All of my applications have been interfacing door lock signals with 5vdc microcontrollers.  A typical circuit consists of a diode on the input to prevent the input from going too negative and a large bias resistor driving a typical NPN transistor.  The output of the transisor then interfaces with our 5vdc logic and works pefectly in our commerical application that has been around for 2+ years with a very small failure rate (and no failures on the door lock circuit).

I've never used a CMOS chip in a car.  Like I said, everything we do is 5VDC, so we use a regulated, filtered power supply to provide a consistent voltage (the single most important part of automotive electrical design).

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Kevin Pierson