11
To fully characterize the start-up sequence of the
power supply under test, measurements must be
made of the output voltage response to the instan-
taneous application of the AC input (see Figure 11).
A digital oscilloscope should be used so that stor-
age of the output values can be accomplished for
the measured start-up time period. To accurately
control the AC input frequency and amplitude to
the power supply under test, a regulated AC source
should be used. Turn-on of the AC source at selected
60 Hz (50 Hz) phases (zero-crossing and positive or
negative peak voltage, for example) is important for
thorough characterization of start-up. The electronic
load used in this test should operate in CR mode.
Figure 10. Voltage Latch-Up
Undesirable voltage latch-up and turn-on can cause the power supply to operate at
current levels that may be damaging to internal circuitry.
Figure 11. Start-Up Delay Test Configurations and Results
