AN1537 datasheet(12/18 Pages) STMICROELECTRONICS

12 / 18 page

AN1537 APPLICATION NOTE

12/18

Figure 16. 80W AC-DC adapter with PFC: Pin (@ Pout = 0) and fsw vs. ambient temperature

The diagrams in figure 15 illustrate the relationship between output current, input voltage and switching fre-

quency obtained with the modified oscillator. Unlike the previously considered design, in this case the internal

propagation delay of the current sense pin is not compensated, then VCOMP changes slightly with the input volt-

age and then there is a variation of the oscillator frequency.

The diagrams of figure 16 illustrate the very limited temperature effect on both the oscillator frequency and the

no-load input consumption at both nominal voltages in the temperature range 0-70 °C.

Figure 17. 80W AC-DC adapter with PFC, flyback section: waveforms @ Pout = 80W

Figure 18. 80W AC-DC adapter with PFC, flyback section: waveforms @ Pout = 30W

-20

0.24

0.26

0.28

0.3

0.32

0.34

Tamb[°C]

fsw [kHz]

Pin [W]

fsw

Pout = 0 W

Vin = 110 Vac

-20

0.36

0.38

0.4

0.42

0.44

0.46

Tamb[°C]

fsw [kHz]

Pin [W]

fsw

Pout = 0 W

Vin = 230 Vac

Q2 Drain

RCT (pin 2 of L5991)

Vin = 110 Vac, Pout = 30W

Vin = 230 Vac, Pout = 30W

Q1 Drain

RCT (pin 2 of L5991)

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