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Don’t Blame Me – I’m Only the Circuit Protection Designer!

Seen any TV Repair Service trucks on your street lately? No? Have you ever taken a piece of electronics gear to a repair shop? Never? Really?? It’s not that electronic equipment doesn’t fail – it’s just that the repair bill would likely exceed the cost of a replacement product. No one knows how much of the electronic trash in our landfills was put there because of technical obsolescence and how much was tossed before the end of its useful life because it failed.

I’ve already expressed my view about how failures due to outside surge events (ESD, induced lightning surges or incidental power line contact) could be drastically reduced with a “Surge Star” program. Today I repaired a stereo amplifier that had suffered a component failure. The amplifier was less than 8 years old and had seen only light usage. What upsets me is that, as a circuit protection designer, I was powerless to prevent this one…

The component that failed was an electrolytic capacitor. It was in a power supply circuit as a filter capacitor. The capacitor itself was 100uF and was rated at 25V. In the circuit it was in parallel with a 15V zener diode. That means that (unless the zener diode failed – which it didn’t) the capacitor would never see more than 60% of its rated voltage in the forward direction and less than 1V in the reverse direction. As a circuit protection designer, I couldn’t have done it better. There is no way this capacitor failed due to external circumstances!

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Mouser Electronics

Mouser Electronics, a Berkshire Hathaway company, is an award-winning, authorized semiconductor and electronic component distributor focused on rapid New Product Introductions from its manufacturing partners for electronic design engineers and buyers. The global distributor’s website,, is available in multiple languages and currencies and features more than 5 million products from over 750 manufacturers. Mouser offers 23 support locations around the world to provide best-in-class customer service and ships globally to over 600,000 customers in more than 220 countries/territories from its 750,000 sq. ft. state-of-the-art facility south of Dallas, Texas.

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