I have a question regarding input protection of a circuit. I have been looking all over the internet for awnsers, but can't seem to synthesize the right solution for my problem.
To make my question as clear as possible I simplefied my circuit to the following:
I am building a modular system that uses a jack connection to pass through a voltage signal. This signal will pass through the middle of the jack plug (A_1). The sense pin leading to S_1 will detect whether the jack is fully inserted. The voltage singal being send through is the voltage over a potentiometer.
Now there are two thing I want to protect the analog signal (A_1) and sense signal (S_1) against. This being ESD (Electrostatic discharge), and a constant too high voltage. My system operates within a voltage range of 0 to 5V. The solution for ESD seems rather obvious, I want to use a LittelFuse TVS diode for that. But there is a possiblitity of a wrong jack connector being inserted and a constant 12V signal passing into my circuit. From research I found out that this TVS diode won't be able to handle this constant higher voltage and I need additional protection. I thought about using a TVS diode and Zener diode in parralel but according to the internet this was not ideal either, since my capacitance will increase and I could have more current leakage.
So I was wondering if any of you guys had a solution or case related to this problem, that can send me in the right direction. Hopefully I explained my question clearly, if not, make sure to shoot me a message.
Thanks in advance.
Edit: since it was unclear how the remainder of the circuit looked I wanted to elaborate a bit futher.
I want to have 32 of these jack connections on my controller (it will become a modular midi controller) The 2 signals lead to two 4051BE multiplexers, from these multiplexers signals lead back to the ATmega32U4 where I read the voltage over the modular parts inserted (A_1) and I read whether jack plugs have been fully inserted (S_1). The modular parts that will be inserted on the midi controller will contain potentiometers. I want to add protection near every of the 32 inputs on my modular midi controller since it is prone to wrong inserts or external disruptions in usage. Hopefully this makes my problem a bit more clear.
Best Answer
Do you want to protect against ESD or do you want to protect your inputs from higher than 5V at the input.
If you want to protect against ESD, anything above the maximum allowed voltage on the contacts should be shorted to ground. There are TVS diodes for many different voltages, so you could choose one for maybe 15-20V or even 30V. That way the 12V will not be passing through it at all, and only high-voltage transients will be shorted to ground.
If you want to limit your input to 5V regardless of the voltage coming in, you could use a medium value resistor like 330-1000 ohms in series, and then a 5.6V zener across the signal line (between the positive end and the ground). You could also place two such zeners back to back to protect against over-voltage of both polarities. You can also try 5.1V zeners and 1k resistors and see how that works for you. Basically, the higher the resistor value, the lower the current through the resistor and the zeners, which reduces wasted power and added heat at higher input voltages, plus it improves the protection.
simulate this circuit – Schematic created using CircuitLab
TVS diodes are almost a million times faster than zener diodes, but since you have these resistors and a slight zener capacitance, that will provide some latency and reduction of the ESD pulse before the zener even starts conducting. Circuits usually have some inertia (impedance) and the fastest transients usually don't go too far. But you could include TVS diodes instead of zeners here. There is a 5V bidirectional TVS diode by Diodes Inc, model number DESD5V0U1BB-7. No need to parallel them with zeners, TVS can work just like a zener, only faster.
NOTE: I see that you are using this for a binary signal. I just want to warn anyone thinking they can use this kind of protection with an audio signal that it would cause distortion for signal voltage peaks above 5V.