Philips 7629 Service Manual page 86

For a more detailed description of one burst cycle, three time intervals are defined:
t1: Discharge of V
transferred, which result in a ramp-up of the output voltage (V
stabilizer. When enough energy is stored in the capacitor, the IC will be switched
'off' by a current pulse generated at the secondary side. This pulse is transferred
to the primary side via the opto coupler. The controller will disable the output
driver (safe restart mode) when the current pulse reaches a threshold level of 16
mA into the Ctrl pin. A resistor R
coupler, to limit the current going into the Ctrl pin. Meanwhile the V
discharged but has to stay above V
t2: Discharge of V
V is discharged to V
CC
load.
t3: Charge of V
UVLO is reached. The internal current source charges the V
the soft start capacitor is recharged). Once the V
start-up voltage, the driver is activated and a new burst cycle is started.
Figure:
when gate drive is active During the first interval, energy is
CC
(R3519) is placed in series with the opto
1
when gate drive is inactive During the second interval, the
CC
.The output voltage will decrease depending on the
UVLO
when gate drive is inactive The third interval starts when the
CC
.
UVLO
capacitor is charged to the
CC
) in front of the
STAB
capacitor is
CC
capacitor (also
CC