millivoltmeter protection

Hi to everybody,

I need to protect a 200 mV (digital) millivoltmeter from over-voltage and reverse voltage input up to +/-30V (the device does not have an internal protection).

Would be useful to put in anti-parallel to it a germanium diode acting as a 0,2V zener ?

Any better ideas well accepted

Thanks a lot
Gianni

 

The germanium diode is a good idea, but you want to also have a lot of series resistance....germanium diodes make lousy fuses!

eric

 

A diode starts conducting at a very low voltage when its current is low.
A germanium diode has a lot of leakage current due to temperature.

An ICL7106 LCD digital voltmeter IC is Cmos. Like all other Cmos ICs its max allowed input voltage is the same as its supply voltages and if the current is limited to 100uA then any voltage is fine.

Its input resistance is Gig-ohms so a series current-limiting resistor does not affect its accuracy.