STMicroelectronics STEVAL-IHT008V1 User Manual page 22

Inrush-current limitation
time of deviation exceeding 3.3%. Here, the output capacitor is charged in 550 ms and
compliance with IEC 61000-3-3 is achieved.
It should also be noted that the peak current during output capacitor charge is not constant.
Indeed, only the step of the reduction of the T_ICL Triac turn-on delay is constant. Hence,
depending on when this Triac turns on, the peak current can vary slightly from one period
to another.
It can also be noted that we have limited the inrush peak current to below 17.4 A, but the
IEC 61000-3-3 limit actually applies to the RMS current. As the T_ICL Triac conducts for a
few hundred microseconds each half-cycle, the RMS current is much lower than the peak
value. Figure 16: "(a) Board operation during 1-cycle line interruption"
the Triac current for the highest peak current event measured in
zoom for the highest peak current during
RMS current equals then 2.45 A, which is much lower than the measured 17.4 A peak
current.
This figure also shows that the output DC voltage is increased by 12 V during this single
Triac conduction.
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Figure 15: Triac current zoom for the highest peak current during start-up
DocID029048 Rev 1
start-up". The Triac conduction lasts 560 µs, its
UM2027
gives of a zoom of
Figure 15: "Triac current