AN3339 datasheet(13/44 Pages) STMICROELECTRONICS

13 / 44 page

AN3339

Functional check

Doc ID 18449 Rev 2

13/44

Functional check

Standby supply

In Figure 9 and 10 some waveforms of the standby supply under rated load operation are

reported. It is based on the VIPER27LN, a device integrating the controller and MOSFET in

a single DIP-7 package. The VIPER27LN works with fixed switching frequency at about 60

kHz, with frequency jittering to reduce EMI. In order to obtain a good efficiency and to

reduce transformer size the converter has been designed to operate in continuous

conduction mode at low mains (Figure 9) and discontinuous conduction mode at high mains

(Figure 10) if PFC and resonant are not working.

In Figure 11 the converter waveforms are captured once the PFC is working. The small

value of the standby transformer leakage inductance allows limited dissipation on the

clamping network across the primary winding. In addition, the drain peak voltage is well

below the VIPER27LN rating even with maximum input voltage and full load operation.

Waveforms relevant to the secondary side are represented in Figure 12: the maximum

reverse voltages applied to the rectifier are well below the component maximum ratings.

Figure 9.

Standby supply waveforms at 115

Vac - 60 Hz - full load

Figure 10.

Standby supply waveforms at 230

Vac - 50 Hz - full load

CH2: VDD (pin #2)

CH1: DRAIN (pin #8)

CH3: CONT (pin #3)

CH4: FB (pin #4)

CH2: VDD (pin #2)

CH1: DRAIN (pin #8)

CH3: CONT (pin #3)

CH4: FB (pin #4)

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