Opto-isolator/ optocoupler for electric isolation in IC design.

[Alex_Bam]

Hello everyone.

I came across while reading the opto-isolator technique used for electric isolation in embedded systems/ Integrated Circuits design that " Opto-isolator is not recommended for electric isolation in power applications IC's mainly due to its dV/dt sensitivity". So I would like to know:

1)How dV/dt sensitivity affects isolation?

2)Is dV/dt sensitivity the only reason to avoid optocoupler especially in power application IC/embedded systems?

3)Are there other limitations in optocoupler which can compel one to chose other isolation techniques?

Looking forward to your suggestions and guidance. Thanks.

 

[bertus]

Hello,

What kind of optocoupler are you looking for?
There are high speed optocouplers with Diac and gate outputs:
https://www.vishay.com/docs/84925/vot8026ab.pdf
https://www.vishay.com/docs/83683/sfh6700.pdf

Bertus

 

[Alex_Bam]

Hello,

What kind of optocoupler are you looking for?
There are high speed optocouplers with Diac and gate outputs:
https://www.vishay.com/docs/84925/vot8026ab.pdf
https://www.vishay.com/docs/83683/sfh6700.pdf

Bertus

Thanks, @bertus. Actually, I was searching for limitations of the optocoupler technique used for electric isolation within IC.

 

[bertus]

Hello,

Perhaps this article will tell you more:
https://www.powerelectronictips.com...e established before the optocoupler turns on.

Bertus

 

[Alex_Bam]

Hello,

Perhaps this article will tell you more:
https://www.powerelectronictips.com/why-isolated-digital-inputs-replacing-optocouplers-up-to-300v-systems-tag31/#:~:text=There are many limitations to this approach. First,,must be established before the optocoupler turns on.

Bertus

Thanks, @bertus for sharing this article. I hope it will help me with optocoupler analysis.
Have a good day!

 

[Harald Kapp]

Where did you get that statement from? Sounds like a marketing statement by one of the competitors to optoisolator technology.

1)How dV/dt sensitivity affects isolation?

There is always a capacitance between input (LED) and output (transistor, driver ...) of an optoisolator. According to I = C × dv/dt a high dv/dt will create a proportionally high displacement current from input to output.
But: other types of couplers also exhibit such a capacitance and are therefore sensitive to the effect. There are also optoisolators with very low coupling capacitance to minimize the effect.

2)Is dV/dt sensitivity the only reason to avoid optocoupler especially in power application IC/embedded systems?

dv/dt sensitivity is not a reason not to use optoisolators.
Any kind of isolated coupler (optical, magnetic, capacitive) needs to be protected from high voltage and high current EMC effects (e.g. surge, burst etc.). These protective elements can also be used to reduce dv/dt.

3)Are there other limitations in optocoupler which can compel one to chose other isolation techniques?

Optoisolators are not necessarily the fastest components. But they are suitable for data rates in the MBit/s range.

Beware of such generalized statements. For every application check which components are suitable or not.

 

[Alex_Bam]

Where did you get that statement from? Sounds like a marketing statement by one of the competitors to optoisolator technology.

There is always a capacitance between input (LED) and output (transistor, driver ...) of an optoisolator. According to I = C × dv/dt a high dv/dt will create a proportionally high displacement current from input to output.
But: other types of couplers also exhibit such a capacitance and are therefore sensitive to the effect. There are also optoisolators with very low coupling capacitance to minimize the effect.

dv/dt sensitivity is not a reason not to use optoisolators.
Any kind of isolated coupler (optical, magnetic, capacitive) needs to be protected from high voltage and high current EMC effects (e.g. surge, burst etc.). These protective elements can also be used to reduce dv/dt.

Optoisolators are not necessarily the fastest components. But they are suitable for data rates in the MBit/s range.

Beware of such generalized statements. For every application check which components are suitable or not.

Thanks, @Harald Kapp your explanation helps me a lot in understanding dv/dt sensitivity and optocoupler in general.