Start-Up Sequence - Philips 20PT643F Service Manual

Figure: QR frequency behavior
Point P1 is the minimum frequency f
voltage and maximum output power required by the application. Of course the minimum
frequency has to be chosen above the audible limit (>20 kHz).

Start-Up Sequence

When the rectified AC voltage V
Mains dependent operation level (Mlevel: between 60 and 100 V), the internal 'Mlevel
switch' will be opened and the start-up current source is enabled to charge capacitor
C2521 at the V pin as shown below.
CC
The 'soft start' switch is closed when the V
capacitor C (C2522, between pin 5 and the sense resistor R3526), is charged to 0.5
SS
V.
Once the V capacitor is charged to the start-up voltage V
CC
driving the MOSFET. Both internal current sources are switched 'off' after reaching this
that occurs at the specified minimum input
MIN
(via the center tap connected to pin 8) reaches the
IN
reaches a level of 7 V and the 'soft start'
CC
-start (11 V), the IC starts
CC