AN2640

PFC section design criteria

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1.2

Boost inductor

To define the PFC inductor several parameters are involved. The formula used to obtain the

inductance value is:

Equation 2

Where

●

●

●

●

●

ηis the estimated efficiency (0.9)

For multipower ballast the inductance calculation must be performed adopting the maximum

lamp power (85 W).

Using these parameters L = 1.95 mH.

An inductance value of 2 mH ± 5% is chosen.

The switching frequency of PFC power transistor can be obtained using the following

formula:

Equation 3

Notice that increasing the inductance value L decreases the PFC switching frequency.

1.3

PFC devices selection

The PFC is a step-up "Boost" regulator, therefore in normal operation the energy is fed from

the inductor to the load and then stored in the output capacitor

Figure 2.

The step-up "Boost" regulator

L

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