AN3286 datasheet(39/42 Pages) STMICROELECTRONICS

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AN3286

Test equipment and measurement of efficiency and light load performance

Doc ID 17998 Rev 1

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is negligible at heavy loads, when the UUT’s input current is much higher than the

voltmeter's leakage current.

On the other hand, at light load conditions, when the UUT’s input current decreases and

approaches the voltmeter’s leakage current, the measurement error introduced with this

setting becomes significant.

To conclude, it is possible to say that the setting shown in Figure 52 should be used for light

loads and standby measurements, while the setting in Figure 53 for heavy loads and

efficiency measurements. If it is not clear which measurement scheme has the least effect

on the results, you can try with both and register the input power’s lower value.

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

are stable. The UUT should be operated at 100% of the nameplate output current output for

at least 30 minutes (warm-up period) immediately prior to conducting efficiency

measurements. After this warm-up period, the AC input power should be monitored for

a period of five 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

the measurements can be recorded at the end of the five minute period.

If the AC input power is not stable over a five minute period, the average power or

accumulated energy should be measured over time for both the AC input and DC output.

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

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

input power is calculated by dividing the measured energy by the integration time itself.

AN3286 数据表(PDF) 39 Page - STMicroelectronics