Implementing NCP1207 in QR 24 W AC-DC Converter with Synchronous Rectifier

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Implementing NCP1207 in QR 24 W AC-DC Converter with Synchronous Rectifier
The NCP1207 is a controller dedicated for driving the
current-mode free running quasi-resonant Flyback offline
converter.
This converter is designed for consumer products like
notebooks, offline battery chargers, consumer electronics
(DVD players, set-top boxes, TVs), etc.
The growing interest for EMI pollution reduction,
efficiency improvement, and maximum safety has been
taken into account while designing the NCP1207.
By implementing the NCP1207 one can build a power
supply that can meet all those requirements. This can be
achieved with help of the following NCP1207 main
features:
?Current-Mode Control: Cycle-by-cycle primary
current observation is helping to prevent any significant
primary overcurrent which would cause transformer抯
core saturation and consequent serious power supply
failure.
?Critical Mode Quasi-resonant Operation: Prevents the
converter operation in Continuous Conduction Mode in
any input and output condition. It is provided by the
zero crossing detection of the auxiliary winding抯
voltage.
?By addition of the reasonable delay the switch turn-on
instant can be shifted to the minimum (valley) of drain
voltage. This improves EMI noise and efficiency.
?Dynamic Self-Supply: Ensures IC proper operation in
applications where the output voltage varies during
operation like battery chargers. The DSS also supplies
the IC when the overvoltage event is being latched and
converter operation is stopped.
?Overvoltage Protection: By sampling the plateau
voltage on the auxiliary winding, the NCP1207 enters
into latched fault condition whenever the overvoltage is
detected. The controller stays fully latched until the
VCC decreases below 4.0 V, e.g. when the user unplugs
the power supply from the mains outlet and re-plugs it.
The OVP threshold can be adjusted externally.


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