Aug 10, 2017 #1 T tiwari.sachin Full Member level 6 Joined Aug 1, 2009 Messages 341 Helped 3 Reputation 6 Reaction score 3 Trophy points 1,298 Location India Activity points 4,449 I am using a simple circuit as given below. The output of schmitt trigger (FEED_SWITCH) connects to the microcontroller. 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. 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.
I am using a simple circuit as given below. The output of schmitt trigger (FEED_SWITCH) connects to the microcontroller. 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. 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.
Aug 10, 2017 #2 KlausST Advanced Member level 7 Joined Apr 17, 2014 Messages 25,162 Helped 4,868 Reputation 9,757 Reaction score 5,537 Trophy points 1,393 Activity points 168,364 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
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