Datasheet

Main characteristics and circuit description AN2994
6/38 Doc ID 15796 Rev 2
At start-up the L6563S is powered by the Vcc capacitor (C12) that is charged via the
resistors R3 and R4, and then the L4 secondary winding (pins 8-11), and the charge pump
circuit (R5, C10, D5 and D4) generates the Vcc voltage that powers the L6563S during
normal operations.
The dividers R32, R33 and R34 provide the L6563S multiplier with information relating to
the instantaneous voltage used to modulate the boost current. The same information is also
used to obtain the average value of the AC line by the voltage feed-forward (V
FF
) pin. The
dividers R9, R10, R11, R12 and 13 are dedicated to sensing the output voltage while the
dividers R6, R7, R8 and R24 are dedicated to protecting the circuit in case of voltage loop
failures. The line-modulated FOT is obtained by the timing generator components D6, C15,
R15, C16, R16, R31, Q3.
The board is equipped with an input EMI filter designed for a two-wire input mains plug. It is
composed of two stages: a common-mode pi-filter connected at the input (C1, L1, C2, C3)
and a differential-mode pi-filter after the input bridge (C4, L3, C5). It also offers the
possibility of easily connecting a downstream converter and testing the interface signals
managed by the L6563S.