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

Alex_Bam

Sep 28, 2020
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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.
 

Harald Kapp

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Nov 17, 2011
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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

Sep 28, 2020
25
Joined
Sep 28, 2020
Messages
25
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.
 
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