# What caps in power supply?

Joined Dec 4, 2009
328
The Al Caps used in switching power supplies are rated for 2000hrs or at the max 5000hrs. I saw one switching power supply with MTBF of 100,000 hrs. I wonder what kind of caps are used to get such high life?

Joined Dec 26, 2010
2,148
The Al Caps used in switching power supplies are rated for 2000hrs or at the max 5000hrs. I saw one switching power supply with MTBF of 100,000 hrs. I wonder what kind of caps are used to get such high life?
There are several possibilities here, leaving aside the possibility that the power supply MTBF figure was simply exaggerated.

• The capacitor lifetime rating normally applies at some elevated operating temperature. It may include wear out mechanisms that are accelerated at high temperatures, and strictly may be =Mean Time To failure (MTTF) as opposed to a constant failure rate MTBF. Whatever the definition, the capacitor lifetime will be very considerably extended if used at a lower temperature.
• Some equipment (e.g. aerospace) may use special quality components which are not so freely available.
• An MTBF of 100,000 hours may not necessarily mean that the unit will typically last this long. Sometimes the figure given is based on calculations using the theoretically constant failure rate applying during the design life of the product, before wear out mechanisms become significant.

#### gootee

Joined Apr 24, 2007
447
Maybe they used metallized polypropylene film capacitors.

And maybe the power supply was a switchmode type that used a very high switching frequency, requiring much lower values of capacitance than a typical linear supply, so that the mpp film capacitors did not require $20-$50 per hundred μF times some large factor.

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#### JMW

Joined Nov 21, 2011
137