AN4165 datasheet(33/37 Pages) STMICROELECTRONICS

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AN4165

Test equipment and measurement of efficiency and light load performance

Doc ID 023661 Rev 1

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Figure 46.

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 45 can be changed to position 2 (see simplified scheme of Figure 47) 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 47.

Switch in position 2 - setting for efficiency measurements

On the other hand, the position of

Figure 47 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 46 for light load

measurements and

Figure 47 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.

SOURCE

UUT

U.U.T.

INPUT

Voltmeter

Ammeter

Wattmeter

AM11591v1

AM11592v1