PFC waveforms

AN4314

22/31

DocID024821 Rev 2

The intervention of the voltage loop can be set using:

Equation 7

The speed of the voltage loop can be increased by fine-tuning the C11, R10 network. A high

value of C15 slows down the voltage loop reaction, but it filters the output capacitor voltage

ripple, affecting the power factor. In this design a compromise has been found.

5.6

Short-circuit

During a short of the output connector, all the energy stored in the output electrolytic

capacitor C3 is discharged into the output side loop, and no current will flow into the external

LEDs, preventing their failure. The SEA05L CC-CV controller is no longer supplied and it

cannot regulate the loop. A peak high current of 60 A has been measured during 100 ns

flowing from the output capacitor into the output side loop. In order to protect the sense

resistor of the cc-cv controller, a Schottky diode D9 of 80 A surge current (see STPS3150U

datasheet [

7]) has been added in the demonstration board.

After this initial transient the short-circuit protection, described above, senses the feedback

signal and disables the L6564H from the PFC_OK pin (see disable function of the L6564H

[

The behavior of the protection has been tested with positive results over the entire input

voltage range; only the two nominal conditions at 100 V

ac

and 230 V

ac

have been discussed

in this application note.

Figure 22 and Figure 23 show that PFC_OK is pulled to GND when the voltage on the C7

capacitor reaches the value of 3 x Vbe (2 x Vf (LL4148) + BC847C Vbe).

8

9

8

5

.

2

R

R

R

V

V

OVP

+

⋅

=