AN10881
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© NXP B.V. 2011. All rights reserved.
Application note
Rev. 2 — 26 September 2011
70 of 102
NXP Semiconductors
AN10881
TEA1713 resonant power supply control IC with PFC
9.9.1 PFC output voltage variations
When bursting the PFC converter, the resonant control system determines the timing.
This can result in a situation where the PFC cannot maintain a constant output voltage.
the HBC operation limits the time during which the PFC can convert power. This may be
too short. The result is either a lower or a varying output voltage. This also has
consequences for the resonant converter as its input voltage is not the same. The working
conditions change towards a new balance.
The resonant converter must be able to remain operational during these conditions.
It is important to check that the resonant controller has not been stopped because the
input voltage provided by SNSBOOST is too low. This can cause an unacceptable voltage
decrease in the output of the resonant converter.
9.9.2 PFC burst duration
Normally a square SNSOUT pulse leads to equal operation time for PFC and HBC
(see
). If a longer PFC operating time is needed for correct balance, it can be
achieved by adding a capacitor on SNSOUT to create a ramp signal. The PFC starts at a
voltage of 0.4 V, allowing a longer PFC operating time.
9.9.3 Switching between burst and normal operation
Interaction between the PFC converter and resonant converter in the Burst mode can lead
to a situation where the system alternates between Burst mode and Normal mode for
certain output power conditions.
9.9.4 Audible noise during mode transition
As a result of the previously mentioned interactions, a stable situation can occur during
the following operating modes, alternating in time:
•
Resonant burst with short burst time without PFC burst (time too short to start).
•
Resonant burst with long burst time and PFC burst.
•
Normal operation for resonant and PFC bursts.
Fig 48. Example of longer burst time for PFC using ramp on SNSOUT
SNSOUT
PFC
DRAIN
HB
001aal057
