AN4106 datasheet(35/39 Pages) STMICROELECTRONICS

35 / 39 page

AN4106

Test equipment and measurement of efficiency and light load performance

Doc ID 023156 Rev 1

35/39

Figure 43.

Switch in position 1 - setting for standby measurements

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 42 can be changed to position 2 (see simplified scheme of Figure 44) where

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

does not affect the measured input voltage.

Figure 44.

Switch in position 2 - setting for efficiency measurements

On the other hand, the position of

Figure 44 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 the reason why it is better to use the setting of

Figure 43 for light load

measurements and

Figure 44 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 output for at least 30

SOURCE

UUT

U.U.T.

INPUT

Voltmeter

Ammeter

Wattmeter

AM11591v1

AM11592v1

SOURCE

UUT

U.U.T.

INPUT

Voltmeter

Ammeter

Wattmeter

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