Diode as analog line protection

I have the below circuit that will detect the presence of a device by a resistor value that sets an output voltage through a divider circuit. This is the fed into a micro-controller ADC.
Rsense can be changed to either 120, 390, or 1000 ohms. The problem I've see with this is that after a while D1 get's damaged. Not sure why this is happening as the reverse voltage is low as well as the current through D1. Maybe it's a temperature thing, not sure. Any ideas?

I can't see what the purpose of the diode is. It may be getting damaged by static discharge, but the rest of the circuit will be protected against static discharge without it.

What happens if you leave it out?

A quick bit of googling for a datasheet shows the 1N6263 to be a UHF schottky diode.
This may be a bit fragile.

Why not use something like a 1N4007 ?

Why do you need a diode there anyway?
Is the "device" which you are testing inductive in any way?

JimB

JimB said:

A quick bit of googling for a datasheet shows the 1N6263 to be a UHF schottky diode.
This may be a bit fragile.

Why not use something like a 1N4007 ?
Why do you need a diode there anyway?
Is the "device" which you are testing inductive in any way?

JimB

Click to expand...

What is a UHF diode? (used for ultra high frequencies? fragile how?)

This is an old design that I'm trying to improve on, no idea why the diode was added, just trying to figure out why it's going bad.
The device being tested just has a connector with a resistor (Rsense in schematic) it may be removed and connected to use different devices with different resistor values. I have not put a scope on it yet, but maybe there's a spike when Rsense is connected? not sure.

If the diode is failing, what are you going to do about it? As far as I can see you are intending to make some design changes. My suggestion and Jim's is to change the diode.

I think that the the act of removing the Rsense is causing a static discharge which damages the diode. You may not need the diode at all, but a 5 V zener diode would help in dissipating a static discharge.

You said that the diode fails after a while. I could be very difficult to work out exactly why it's failing. Static discharge is very unpredictable. I can't see why finding that out will help, when the solution is to change it anyhow.

The 1N6263 is a UHF schottky diode. The "UHF" means that it has been made with a very small capacitance, so that it will work at high frequencies. Schottky diodes are often faster to switch than conventional diodes and have a lower forward voltage. None of those attributes are of any use in this circuit. All design is compromise, so as the 1N6263 has been made fast and low capacitance, it has resulted in a very small maximum current, a smaller maximum voltage and a higher price compared to a 1N4007.