AN10881
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© NXP B.V. 2011. All rights reserved.
Application note
Rev. 2 — 26 September 2011
64 of 102
NXP Semiconductors
AN10881
TEA1713 resonant power supply control IC with PFC
The comparator input monitors the regulation voltage SNSFB to a preset burst voltage
value by R1 and R2: BURST. When the HBC power output power is low, the regulation
voltage decreases and when it reaches BURST the switching stops by switching
SNSOUT to ground. When the switching stops, no energy is converted and the output
voltage drops. The regulation voltage then increases again. When the regulation voltage
reaches BURST + HYST (voltage hysteresis set by R
HYST
) the switching resumes.
When the power delivered during a burst is larger than needed for the output, the
regulation voltage SNSFB quickly decreases, stopping the switching at BURST. The time
needed for the regulation voltage to reach BURST, is dependent on the output voltage and
its load.
When the HBC output load increases to high levels, normal operation is resumed as the
regulation voltage can no longer reach the BURST level.
9.3 Advantages of Burst mode for HBC
The main reason of applying Burst mode in a resonant converter is to improve the
efficiency at low output power by reducing the power losses.
The graphs in
and
show the improvement principle in an example of a
250 W resonant converter including (non-bursting) PFC.
Fig 40. Improved efficiency by HBC Burst mode in a 250 W converter
Pout (W)
0
50
40
20
30
10
001aal050
40
60
20
80
100
efficiency
(%)
0
with burst mode
with burst mode
normal mode
