AN2982

Designing the application

Doc ID 15599 Rev 1

13/31

1.2.8

Input rectifier

A 2KBP06M bridge rectifier is able to sustain 600 V in reverse condition and 2 A of forward

current. Its maximum power dissipation is equal to:

Equation 29

1.2.9

Input capacitor

Let r = 10% be the maximum allowed ratio between the high-frequency ripple amplitude

seen at the input of the PFC stage and the mean value of the input current:

Equation 30

1.2.10

Input circuitry

The input circuitry is composed of:

–

A fuse: avoids damage due to ballast breaking or excessive current from the

mains

–

An NTC: limits the inrush current which avoids blowing the fuse and reduces the

effects of a burst from the mains. This component reduces its resistance at a

higher temperature. A 5

Ω NTC (at 25 °C) is used

–

A varistor (not present): absorbs the energy associated with a mains surge

MOSFETs, IC,…)

–

An EMI filter: an LC network able to reduce the HF noise coming from the

application and traveling through the mains. This filter has to filter both the

common mode component of the noise (which can be measured between the AC

input and the EARTH) and the differential mode component of the noise (which

can be measured between the two AC inputs)

The first component (the fuse) is filtered by a CM filter (a current transformer that forces the

AC input currents to travel in the opposite way) and two 1 nF capacitor placed between each

AC input and EARTH. The second component (the NTC) is filtered by two capacitors placed

across the AC inputs and by the leakage inductance of the CM filter. In fact by using a CM

transformer having a high leakage inductance, a differential filtering can be obtained. The

W

73

.

1

V

V

P

2

2

P

F

(min)

rms

,

in

in

B

=

=

nF

470

C

nF

87

.

401

V

f

r

2

P

C

in

2

(min)

RMS

,

in

sw

in

min

,

in

min

=

→

=

⋅

⋅

⋅

π

=