AN3028 datasheet(14/37 Pages) STMICROELECTRONICS

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Burst mode and output voltage ripple

AN3028

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Doc ID 16135 Rev 1

Burst mode and output voltage ripple

When the converter is lightly loaded, the COMP pin voltage decreases. As it reaches the

shutdown threshold, VCOMPL (1.1 V, typical), the switching is disabled and no more energy is

transferred to the secondary side. So, the output voltage decreases and the regulation loop

makes the COMP pin voltage increase again. As it rises 40mV above the VCOMPL threshold,

the normal switching operation is resumed. This results in a controlled on/off operation

(referred to as “burst mode) as long as the output power is low enough to require a turn-on

time lower than the minimum turn-on time of the VIPer16LN. This mode of operation keeps

the frequency-related losses low when the load is very light or disconnected, making it

easier to comply with energy-saving regulations.

The figures below show the output voltage ripple when the converter is not loaded or lightly

loaded and supplied with 115 VAC and with 230 VAC respectively.

Table 6

shows the measured value of the burst mode frequency ripple measured in different

operating conditions. The output voltage ripple in burst mode operation is very low.

Figure 14.

Output voltage ripple at 115 VINAC

no load

Figure 15.

Output voltage ripple at 230 VINAC

no load

Figure 16.

Output voltage ripple at 115VINAC

25 mA

Figure 17.

Output voltage ripple at 230VINAC

25 mA

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