AN3118 Datasheet, PDF (17/31 Pages) STMicroelectronics – 250 W transition-mode PFC pre-regulator with the new L6563H

AN3118
Test results and significant waveforms
It is also possible to see, comparing Figure 24 and 25, that the input current of the latter has
a better shape and the 3rd harmonic current distortion is not noticeable; this demonstrates
the benefits of the new voltage feed-forward circuit integrated in the L6563H, allowing a fast
response to mains disturbances to be obtained but using a reasonably long V_FF time
constant also provides very low THD and high PF at the same time, as confirmed by the
measurements in Figure 24 and 25:
Figure 24. L6563 input current at 100 Vac - 50 Figure 25. EVL6563H-250 W TM PFC input
Hz C_FF=0.47 µF, RFF=390 kΩ
current at 100 Vac - 50 Hz C_FF=1 µF,
RFF=1 MΩ
THD= 4.36 %, 3rd harmonic=94.6 mA
CH2: MULT (pin #3)
CH3: V_FF (pin #5)
CH4: I_AC
THD= 2.94 %, 3rd harmonic=30.5 mA
CH2: MULT (pin #3)
CH3: V_FF (pin #5)
CH4: I_AC
Another function integrated in the L6563H is brown-out protection, which is basically a not-
latched shutdown function that must be activated when a mains under voltage condition is
detected. This abnormal condition may cause overheating of the primary power section due
to an excess of RMS current. Brown-out can also cause the PFC pre-regulator to work
open-loop and this could be dangerous to the PFC stage itself and the downstream
converter, should the input voltage return abruptly to its rated value. Another problem is the
spurious restarts that may occur during converter power down and that cause the output
voltage of the converter not to decay to zero monotonically. For these reasons it is usually
preferable to shutdown the device in case of brown-out.
Brown-out function is done by sensing the input mains through an internal comparator
connected to the RUN pin (#12), connected via a divider to the V_FF pin (#5), which delivers a
voltage signal proportional to the input mains. The enable and disable thresholds at which
the L6563H starts or stops the operation can be adjusted by modifying that divider ratio. For
additional information please see [2].
Doc ID 16847 Rev 2
17/31