AN2521 datasheet(13/33 Pages) STMICROELECTRONICS

13 / 33 page

AN2521

Functional check

13/33

Functional check

3.1

Normal operation

Figure 15 and Figure 16 display some waveforms of the flyback stage during steady-state

operation of the circuit at full load and nominal input voltage ranges. Under full load

conditions the L6668 switching frequency has been set to 65 kHz in order to achieve good

efficiency and to limit the switching noise.

It's possible to note that the CH3 relevant to the output voltage of the PFC circuit shows the

tracking boost function setting at a different PFC output voltage (247 / 348 volts), which is

dependent on the mains input voltage as mentioned on the previous page.

In Figure 17 the drain voltage waveforms and the measurement of the peak voltage at full

load and maximum mains input voltage are shown.

The maximum voltage peak in this condition is 676 V, which ensures reliable operation of the

power MOSFET with a good margin against the maximum BVDSS.

Figure 15.

EVAL6668-75W flyback stage

waveforms @115 V, 60 Hz-full load

Figure 16.

EVAL6668-75W flyback stage

waveforms @230 V, 50 Hz-full load

CH1: input mains voltage

CH2: input mains current

CH3: PFC output voltage

CH1: input mains voltage

CH2: input mains current

CH3: PFC output voltage

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