Hi All,

I am having trouble with a 485 line driver which keeps blowing up. I think its due to transient spikes and require a way to protect the driver.

Ideally i want something to protect the driver but capable of withstanding a kV surge.

would opto isolators work? i know they have good input to output isolation but what protects the input or output of the opto from a spike?

If anyone can help that would be great.

Thanks

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There are exactly 10 types of people in the world.
Those who understand binary numbers and those who don’t.

 

Reverse bias a diode with a breakdown voltage slightly above the safe operating voltage, the diode will not conduct under normal operating condiditions but during a surge the diode will break down and the surge will be grounded.

 

You have to know the surge energy you are trying to design the protection for. A zener type device will conduct and try to clamp the surge, but if it is too much energy, it will just blow the zener open and then the surge destroys the device to be protected.

Back when I did this stuff, the best protectors were called Tranzorbs which are like zeners except they have a sharper clamping characteristic and are available in very high energy ratings.

 

Tranzorbs are a brand of TVS Diodes, Transient Voltage Suppression Diodes. They can handle a large amount of energy for a short time, perfect for surge protectors.