Datasheet

AN4165 Test equipment and measurement of efficiency and light load performance
Doc ID 023661 Rev 1 33/37
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.
V
+
-
A
~
AC
SOURCE
UUT
U.U.T.
AC
INPUT
Voltmeter
Ammeter
Wattmeter
AM11591v1
AM11592v1
V
+
-
~
AC
SOURCE
UUT
U.U.T.
AC
INPUT
Voltmeter
Ammeter
A
Wattmeter