Diode Clamp to protect over voltage

[IRE2000]

Hi,
Any input on my dilemma much appreciated, I don't have a background in EE design but I'm trying to solve a issue (limiting the voltage) on the following -

Background - 0-10 DC V supply from external source that is monitored on an input pin of a micro controller
Max Vin allowable on MicroC pin is 1.2V
Step 1 is to use a 220K / 30K Voltage divider producing a 0 to 1.2V input into the pin on the MicroC -
Step 2 is to clamp the voltage at max 1.2V in case the V supply rises above 10V
After doing some research I think that using a diode to clamp the voltage should work - connecting the cathode to a 0.6V rail (another Vdivider 16K/4K3 form 3V3 supply) and the anode to the MicroC pin? is this a logical solution?
It the Diode clamp does work if the 3V3 supply goes down does the Diode still protect the MicroC ?

Many Thanks

 

[Lyker]

Hello IRE200,

No because your diode’s cathode is not being present with a low enough source impedance. Get a couple of silicon diodes in series from your port pin down to 0V (anode on port pin).
These diodes with clamp to around 1.2V at room temp but remember this will reduce by -2.1mV / °C
Hope this helps

 

[IRE2000]

Thanks for reply Lyker, I'll look into this.