Once the V
CC
capacitor is charged to the start-up voltage V
CC-start
(11V), the IC starts
driving the MOSFET. Both internal current sources are switched ‘off’ after reaching this
start-up voltage. Resistor R
SS
(3524) will discharge the ‘soft start’ capacitor, such that
the peak current will slowly increase. This to prevent ‘transformer rattle’.
During start-up, the V
CC
capacitor will be discharged until the moment that the primary
auxiliary winding takes over this voltage.
Figure:
The moment that the voltage on pin 1 drops below the ‘under voltage lock out‘ level
(UVLO = ± 9 V), the IC will stop switching and will enter a safe restart from the rectified
mains voltage.
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