AN4116 datasheet(34/38 Pages) STMICROELECTRONICS

34 / 38 page

Test equipment and measurement of efficiency and light load performance

AN4116

34/38

Doc ID 023220 Rev 1

In the case of high UUT input current (i.e. for measurements in heavy load conditions), the

voltage drop can be relevant compared to the UUT real input voltage. If this is the case, the

switch in

Figure 54 can be changed to position 2 (see simplified scheme of Figure 56),

where the UUT input voltage is measured directly at the UUT input terminal and the input

current does not affect the measured input voltage.

On the other hand, the position of

Figure 56 may introduce a relevant error during light load

measurements, when the UUT input current is low and the leakage current inside the

voltmeter itself (which is not an ideal instrument and doesn't have infinite input resistance) is

not negligible. This is why it is recommended to use the setting of

Figure 55 for light load

measurements and the setting of

Figure 56 for heavy load measurements.

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

and register the lower input power value.

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

Figure 55.

Switch in position 1 - setting for standby measurements

Figure 56.

Switch in position 2 - setting for efficiency measurements

AM13106v1

SOURCE

UUT

U.U.T.

INPUT

Voltmeter

Ammeter

Wattmeter

AM13107v1

SOURCE

UUT

U.U.T.

INPUT

Voltmeter

Ammeter

Wattmeter

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