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Simple Switch AC and DC Coupling Results

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tiwari.sachin

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I am using a simple circuit as given below. The output of schmitt trigger (FEED_SWITCH) connects to the microcontroller.

SWITCH CKT.jpg

Sometimes the cap C49 fails and i need to replace it. The cap voltage is 16V and its a ceramic.

I tested output at pin 2 and pin 4 of U13 selecting DC Coupling on CRO and the output was as desired.

But the moment i selected AC coupling. I got the output as below.

AC Coupling.jpg

Is this voltage adding up on DC and damaging capacitor?

Earlier designs i never used SCH Trigger and MCU IO used to damage.

The results on AC coupling mode was same even when i removed C49 and even D19

If this is possible reason for damage then how can i reduce this effect.
 

Hi,

The scope picture just shows the high_pass behaviour of the scope in AC mode.
It has nothing to do with your failure.

I can't imagine how your capacitor may fail.
Do you expect some ESD problems?
Or maybe a mechanical stress problem with hand soldering?

--> I'd try to buy similar capacitors from a high quality manufacturer.

Klaus
 
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