4.4
Surge robustness
We performed the lightning surge robustness according to the IEC61000-4-5 test. We tested four configurations:
positive and negative surges with 90° and 0° phase angles as shown below.
Figure 15.
IEC61000-4-5 surge test configuration
The EN pin is supplied with 5 V DC, the low side SCRs bypass the NTC, and the PFC output capacitor is already
charged through the NTC.
During the positive surge at the peak line voltage (A configuration), the SCR_N is already positively biased and
conducting. The surge current flows through the SCR_N.
Figure 16.
Waveforms resulting from the 2 kV IEC61000-4-5 test (A configuration)
There are three phases for negative surge test results at the peak line voltage (B configuration):
•
Phase 1: before the surge is applied, the nominal current flows through the SCR_N (positively biased).
•
Phase 2: applying a negative surge, the AC main voltage V
LN
becomes negative and the SCR_N is
negatively biased. The SCR_N turns off and the SCR_L handles the surge current, becoming positively
biased. The
is specified with an ITSM = 950 A for 30 µs pulse. The gate current is switched to
the positive biased SCR, thanks to the gate driver made of
.
•
Phase 3: when the lighting surge is completed, the V
LN
becomes positive again, the SCR_N is positively
biased and turns on. The SCR_L is reversed biased and turns off. The SCR_N handles the nominal current
and the system returns to its normal operation.
UM2948
Surge robustness
UM2948
-
Rev 1
page 11/28
