Datasheet

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 V
DD
has dropped down
to V
DD_RESTART
(4.5 V). At this point the auto-restart process takes place like any startup;
the internal current source charges the V
DD
capacitor until it reaches the V
DDon
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: V
DD
(pin #2)
CH3: +5 V standby
CH4: FB (pin #4)
CH1: DRAIN (pin #8)
CH2: V
DD
(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: V
DD
(pin #2)
CH3: +5 V standby