varistor for overvoltage protection?!

[stoyanoff]

Greatings! I`m using an etalon resistor for measuring current in high voltage circuit. I`m using 0.01 ohm resistor and OA(the attached file). There is a chance the voltage drop on the resistor to reise dramaticly in malfunction of the device. So I want to put somekind of protection. I want to be sure in case of malfunction my chart will stay untouched.

So I want to use varistor. I`m not sure if I must just put a varistor in paralel with the resistor. I found in shops varistor 10К. I don`t know do i have to calculate the value of this varistor or just to put one at the entrance???
Is it a good idea to use a cener diode???

 

[paulfjujo]

hello

I found in shops varistor 10К.

Varistor has a working nominal voltage ? Resistor value is not enough data .
You can add some resistor in serial of each input
and 2 diodes to limit amplitude on the amplifier input.
and maybe un condensator to avoid spike wich can destroy all, even with diodes
due to time response of diodes

i suppose that the voltage accross the shunt can't be over 100mV ..
you didn't specify what is the maximum Amp.

and add a fuse of 50 mAmps or 0,1A to protect the diodes .

 

[mister_rf]

A typical protection circuit for the shunt measurement use a resistor instead of the low current fuse. But... before we start designing some overvoltage protection, there’s a more critical unsolved problem, see this topic:

https://www.edaboard.com/threads/248829/#post1065876

That’s a very high input common-mode voltage range, up to 450V! Need to solve the high-side current shunt monitor design first.

 

[stoyanoff]

I think the max voltage on the shunt is around 0.40V. I have a question. If I put diodes(or cener diode 3.3V for example) should this interаct with the Rshunt and encrease it`s resistence and the voltage drop??

 

[mister_rf]

No, use some simple diodes and resistors, but first check the chosen part’s data sheet for internal protection. When necessary, protection diodes D5-D6 should be added to guarantee prevention of circuit breakdown. Ordinary low capacitance diodes will suffice, such as the 1N4148 family. Add current limiting resistors as necessary, to limit diode current to safe levels.

 

[james305021]

We are a professional varistor manufacturer in china .

A varistor is an electronic component with a "diode-like" nonlinear current–voltage characteristic. The name is a portmanteau of variable resistor. Varistors are often used to protect circuits against excessive transient voltages by incorporating them into the circuit in such a way that, when triggered, they will shunt the current created by the high voltage away from the sensitive components. A varistor is also known as Voltage Dependent Resistor or VDR. A varistor’s function is to conduct significantly increased current when voltage is excessive.

Varistor always put in first position in PCB .