AN3329 datasheet(13/47 Pages) STMICROELECTRONICS

13 / 47 page

AN3329

Functional check

Doc ID 18376 Rev 1

13/47

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: VDD (pin #2)

CH4: FB (pin #4)

CH1: DRAIN (pin #8)

CH3: CONT (pin #3)

CH2: VDD (pin #2)

CH4: FB (pin #4)

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