Datasheet

AN3172 Functional check
Doc ID 17230 Rev 1 15/31
4.1 Standby and no-load operation
In Figure 11 and Figure 12, some burst-mode waveforms are given. As seen, both L6599A
and L6563H operate in burst-mode. In Figure 11 it may also be noted that PFC and LLC
bursts are synchronized.
In Figure 13 and 14 the transitions from full load to no-load and vice versa, at maximum
input voltage, have been checked. The maximum input voltage has been chosen because it
is the most critical input voltage for transition; in fact at no-load the burst pulses have the
lower repetition frequency and the Vcc may drop, causing restart cycles of the controller. As
seen in Figure 13 and 14, both transitions are clean and there isn't any output voltage or Vcc
dip.
Figure 9. Rectifier waveforms Figure 10. Startup waveforms
CH1: D23 anode voltage CH2: D24 anode voltage CH1: HB voltage CH2: Vout PFC
CH3: D23 current CH4: D24 current CH3: Vcc CH4: Output voltage
Figure 11. No-load operation Figure 12. No-load operation - detail
CH1: Q4 gate CH2: PFC gate voltage CH1: Q4 gate CH2: PFC gate voltage
CH3: STBY pin CH4: Output voltage CH3: STBY pin CH4: Output voltage