would opto isolator function with dc bias?

[nagashr]

i am searching for a better over voltage protection circuit.

In order to achieve that i want to use an optocoupler.But the thing is whether it would work for dc bias or not.can anyone help me out...

[Buechsenschuetz]

I think the term "dc bias" means that you want to transfer a dc voltage via an isolator. 

Usually opto isolators have a LED as transmitter and a photodiode as sensor. Both will not necessarily work linear. Also, a photodiode needs a current source to "drive" it, since usually the increase of leakage current (reverse current) of the photodiode is used to detect light radiation from the input LED. 

There are also so-called "photovoltaic opto isolators". These have one or several photodiode switched in series at the output and they will generate a DC voltage at the output (without any external current/voltage source) when a dc voltage is applied to the input LED. International Rectifier used to make such devices. 

[Dick-Thee]

I read your article about over and under voltage from 2013. I'm working on a circuit like that based on and Pulse position modulator using a NE555 and the galvanic isolation with an Optocoupler.  I use a an 555 to create a pulse position modulator followed by and optocoupler to  create the galavanic isolation. The relation between the line piek voltage  and the pulse witdh of the NE555 is logarimic. It can be used to detect citical line voltage levels. This citcuit has a 11ms pulse for 100Vrms line voltage and 30ms for 140Vrms lines.  I'm planning to monitor the network in mexico with this circuit.

I have problems simulating optocouplers in multisim but  found a soluction by using a feedback resistor connected to the bias input of the optocoupler. Why I can't get the optocouplers to work as normal without bias I dont know. I think it has to do with the spice models I guess. If you can help me with simulating CNY17-1 optos I'll be happy.

I added the circuit in case you still have intrested in it.

Regards oscar goos