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Board/Components Protection

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Akanimo

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Hi,

I am to make the circuit as in the diagram attached. The connector is to connect some offboard component. There is possibility that there might be a surge due to ESD, etc.

The current through the opto LED is 10mA maximum in normal operation.

I am considering protection of the opto and of course the board from such surges should they occur.

What would be the most appropriate way to do this?
IMG_20201202_105508.jpg
 

KlausST

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Hi,

there were several discussions about ESD protection. Some in the near past.

I´d say the opto is useless here. It is an isolating device, but since input and ouput refer to the same GND ... it´s isolating function is useless.
Some "try" to use an opto as "protection" device. But it is no protection device.
Instead it is a device that may cause failure, it will degrade performance with time and it means additional cost.

Klaus
 

    Akanimo

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Akanimo

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Hi,

there were several discussions about ESD protection. Some in the near past.

I´d say the opto is useless here. It is an isolating device, but since input and ouput refer to the same GND ... it´s isolating function is useless.
Some "try" to use an opto as "protection" device. But it is no protection device.
Instead it is a device that may cause failure, it will degrade performance with time and it means additional cost.

Klaus
The ground is now well separated.

Also, I have made the design with the opto for long term reliability, so I'm not bothered about using it.

I need to protect the primary side of the opto though. So I am considering the cost effectiveness of the RC snubber and the capability of the TVS diode. What would you advise?
 

Akanimo

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Thanks Klaus.

I found another way to deal with the issue. The circuit is very much improved by positioning the connector between the diode and ground and connecting an antiparallel diode across the opto LED.
 

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