AN3329 datasheet(16/47 Pages) STMICROELECTRONICS

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Functional check

AN3329

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Doc ID 18376 Rev 1

and switching starts again. This protection and restart sequence lasts as long as the OVP

condition is removed. It is important to highlight that the Viper27LN OVP protection, thanks

to the internal logic, ensures a stable OVP intervention point, independent of the output

load, even if the voltage sensing is done on auxiliary winding at primary side. It can be

noted, by comparing Figure 21 to Figure 23 which report some OVP intervention with

different loads and input voltage conditions, that the maximum output voltage peak has a

negligible variation.

Figure 24 shows, in detail, the OVP intervention at 115 Vac. In Figure 25 a short-circuit

event on the standby supply output has been captured. In this situation the Viper27LN

enters a safe hiccup mode, providing protection against overheating of the auxiliary

converter power components.

Figure 23.

Standby supply OVP at 115 Vac -

60 Hz - PFC on - 1 A

Figure 24.

Standby supply OVP at 115 Vac -

60 Hz - PFC on - 1 A

CH1: DRAIN (pin #8)

CH2: +5 V standby

CH3: CONT (pin #3)

CH4: FB (pin #4)

CH1: DRAIN (pin #8)

CH2: 5 V standby

CH3: CONT (pin #3)

CH4: FB (pin #4)

Figure 25.

Standby supply output short-circuit

at 230 Vac - 50 Hz, full load

Figure 26.

Standby supply output short-circuit

at 230 Vac - 50 Hz, full load - detail

CH1: DRAIN (pin #8)

CH2: +5 V standby

CH3: VDD (pin #2)

CH4: FB (pin #4)

CH1: DRAIN (pin #8)

CH2: 5 V standby

CH3: VDD (pin #2)

CH4: FB (pin #4)

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