Datasheet

AN3329 Functional check
Doc ID 18376 Rev 1 13/47
4 Functional check
Standby supply
Some salient waveforms of the standby supply during full load operation are reported in
Figure 13 and 14. This converter is based on the Viper27LN, a device integrating the
controller and the MOSFET in a single DIP-7 package. The Viper27LN version operates in
fixed frequency mode at about 60 kHz, and frequency jitter technique is implemented to
reduce EMI noise. In order to obtain good efficiency as well as reduced transformer size the
converter has been designed to operate at full load in continuous conduction mode at low
mains voltage (Figure 13) and discontinuous conduction mode at high mains voltage
(Figure 14), once the PFC and resonant stages are off. It can be noted from the drain
waveforms that the typical ringing at turn-off is limited, thanks to the small value of the
transformer's primary leakage inductance, allowing limited power dissipation on the Transil
diode D19 and therefore enhancing the efficiency at rated load. D19 acts as a clamper and
allows to limit the drain peak voltage below the Viper27LN maximum rating even with
maximum input voltage and full load operation.
In Figure 15 the converter waveforms are captured while the PFC is working and the
standby supply is powered with 400 V. The margin with respect to the Viper27LN maximum
drain voltage can be noted on the sidebar on the right.
In Figure 16 typical waveforms relevant to the secondary side have been captured; the
maximum reverse voltages applied to the rectifier at 400 V during full load operation with
PFC working are, even in this case, well below the component's maximum ratings, ensuring
long term reliability.
Figure 13. Standby supply waveforms at
115 Vac - 60 Hz, full load
Figure 14. Standby supply waveforms at
230 Vac - 50 Hz, full load
CH1: DRAIN (pin #8)
CH3: CONT (pin #3)
CH2: V
DD
(pin #2)
CH4: FB (pin #4)
CH1: DRAIN (pin #8)
CH3: CONT (pin #3)
CH2: V
DD
(pin #2)
CH4: FB (pin #4)