DocID025078 Rev 1

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AN4345

Test equipment and measurement of efficiency and light load performance

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If it is not clear which measurement scheme has the lesser effect on the result, both of them

should be tested and then, the lower input power value should be registered.

As noted in IEC 62301, instantaneous measurements are appropriate when power readings

are stable. The UUT is operated at 100% of nameplate output current for at least 30 minutes

(warm-up period) immediately prior to conducting efficiency measurements.

After this warm-up period, the AC input power is monitored for a period of 5 minutes to

assess the stability of the UUT. If the power level does not drift by more than 5% from the

maximum value observed, the UUT can be considered stable and measurements can be

recorded at the end of the 5-minute’s period. If AC input power is not stable over a 5-

minute’s period, the average power or accumulated energy is measured overtime for both

AC input and DC output.

Some wattmeter models allow integration of the measured input power in a time range and

then measure the energy absorbed by the UUT during the integration time. The average

input power is calculated dividing by the integration time itself.