AN3329 datasheet(15/47 Pages) STMICROELECTRONICS

15 / 47 page

AN3329

Functional check

Doc ID 18376 Rev 1

15/47

Figure 19 and Figure 20 illustrate the waveforms during light load operation. Viper27LN

operates in burst-mode, with just a few pulses per burst, minimizing switching losses and

therefore improving efficiency under light load operation, making it suitable for equipment

with low standby consumption requirements.

Figure 21 shows the OVP response, observed opening the Viper27LN feedback loop. If the

output voltage value exceeds the internal threshold set by the resistor divider connected to

the CONT pin (#3), the Viper27LN stops working, providing protection against dangerous

voltages which may damage the system. It remains latched until the VDD has dropped down

to VDD_RESTART (4.5 V). At this point the auto-restart process takes place like any startup;

the internal current source charges the VDD capacitor until it reaches the VDDon threshold

Figure 19.

Standby supply burst mode

operation at 230 Vac - 50 Hz - 10 mA

load

Figure 20.

Standby supply burst mode

operation at 230 Vac - 50 Hz - 10 mA

load-detail

CH1: DRAIN (pin #8)

CH2: VDD (pin #2)

CH3: +5 V standby

CH4: FB (pin #4)

CH1: DRAIN (pin #8)

CH2: VDD (pin #2)

CH3: +5 V standby

CH4: FB (pin #4)

Figure 21.

Standby supply OVP at 115 Vac -

60 Hz, full load

Figure 22.

Standby supply OVP at 230 Vac -

50 Hz - 0.5 A

CH1: DRAIN (pin #8)

CH2: +5 V standby

CH3: CONT (pin #3)

CH4: FB (pin #4)

CH1: DRAIN (pin #8)

CH2: VDD (pin #2)

CH3: +5 V standby

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