Datasheet

AN4165 Burst mode and output voltage ripple
Doc ID 023661 Rev 1 15/37
7 Burst mode and output voltage ripple
When the converter is lightly loaded, the COMP pin voltage decreases. As it reaches the
shutdown threshold, V
COMPL
(1.1 V, typical), the switching is disabled and energy is no
longer transferred to the secondary side. So, the output voltage decreases and the
regulation loop makes the COMP pin voltage increase again. As it rises 40 mV above the
V
COMPL
threshold, the normal switching operation is resumed. This results in a controlled
on/off operation (referred to as “burst mode”) as long as the output power is low enough to
require a turn-on time lower than the minimum turn-on time of the VIPER26. This mode of
operation keeps the frequency-related losses low when the load is very light or
disconnected, making it easier to comply with energy-saving regulations. The figures below
show the output voltage ripple when the converter is not (or lightly) loaded and supplied with
115 V
AC
and with 230 V
AC
respectively.
Figure 16. Output voltage ripple at
V
IN
=115V
AC
, no load
Figure 17. Output voltage ripple at
V
IN
= 230 V
AC
, no load
AM13370v1
AM13371v1
Figure 18. Output voltage ripple at
V
IN
=115V
AC
, I
OUT
= 25 mA
Figure 19. Output voltage ripple at
V
IN
= 230 V
AC
, I
OUT
= 25 mA
AM13372v1
AM13373v1