1. Lifetime Calculation When Conditions Change

Suppose a power supply is used for A hours under condition a, for B hours under condition b, … and for X hours under condition x. Let the estimated lifetime under each condition be La, Lb, …, Lx.
Then the estimated lifetime L under these combined (mixed) conditions is calculated as follows.

2. Example

Electrolytic capacitor

Rated Temperature = 105℃
Basic Lifetime = 1,000H

Operating conditions

45℃ (Estimated lifetime = 64,000H) / 8H
55℃ (Estimated lifetime = 32,000H) / 8H
65℃ (Estimated lifetime = 16,000H) / 8H

According to formula ①,

The ambient temperature (Ta) used in the above estimated lifetime calculation can be obtained from the following formula.

As a result, Ta (57.2°C) is higher than the average ambient temperature of 55°C, which means that the actual operating condition is more severe than operating continuously at the average ambient temperature.