AN4149 datasheet(36/43 Pages) STMICROELECTRONICS

Part #	AN4149

Description	Designing a CCM PFC pre-regulator based on the L4984D

PDF	43 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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36 / 43 page

FOT PFC boost control loop

AN4149

36/43

DocID023523 Rev 2

Equation 104

From equation 90 and equation 104 the actual 3rd harmonic distortion can be found:

Equation 105

The comparison between Figure 20 and Figure 21 shows the practical difference between

two different configurations of compensation network. In the first case, where the series

resistor R2 is such to move the "phase boost" far from the crossover frequency, the phase

margin is very low (around 22 °) then the system is underdamped, experiencing large

overshoots and ringings. In the second case where the phase margin is around 56 ° the

response of the system to the load variation is fast and without ringing, thus with limited

deviations.

Figure 20. 115 Vac step load (50 % to 100

%): improper compensation

Figure 21. 115 Vac step load (50 % to 100

%): good compensation

() 011

min

⋅

LINE

253

100

⋅

−

⋅

ref

COMP

out

AN4149 Datasheet(PDF) 36 Page - STMicroelectronics