NCL30080
www.onsemi.com
11
Application Information
The NCL30080 implements a current−mode architecture
operating in quasi−resonant mode. Thanks to proprietary
circuitry, the controller is able to accurately regulate the
secondary side current of the flyback converter without
using any opto−coupler or measuring directly the secondary
side current.
• Quasi−Resonance Current−Mode Operation:
implementing quasi−resonance operation in peak
current−mode control, the NCL30080 optimizes the
efficiency by switching in the valley of the MOSFET
drain−source voltage. Thanks to a smart control
algorithm, the controller locks−out in a selected valley
and remains locked until the input voltage or the output
current set point significantly changes.
• Primary Side Constant Current Control: thanks to a
proprietary circuit, the controller is able to compensate
for the leakage inductance of the transformer and allow
accurate control of the secondary side current.
• Line Feed−forward: compensation for possible
variation of the output current caused by system slew
rate variation.
• Open LED protection: if the voltage on the VCC pin
exceeds an internal limit, the controller shuts down and
waits 4 seconds before restarting switching.
• Brown−Out: the controller includes a brown−out
circuit with a validation timer which safely stops the
controller in the event that the input voltage is too low.
The device will automatically restart if the line recovers.
• Cycle−by−cycle peak current limit: when the current
sense voltage exceeds the internal threshold V
ILIM
, the
MOSFET is turned off for the rest of the switching cycle.
• Winding Short−Circuit Protection: an additional
comparator with a short LEB filter (t
BCS
) senses the CS
signal and stops the controller if V
CS
reaches 1.5 x
V
ILIM
. For noise immunity reasons, this comparator is
enabled only during the main LEB duration t
LEB
.
• Output Short−circuit protection: If a very low
voltage is applied on ZCD pin for 90 ms (nominal), the
controllers assume that the output or the ZCD pin is
shorted to ground and enters shutdown. The auto−
restart version (B suffix) waits 4 seconds, then the
controller restarts switching. In the latched version (A
suffix), the controller is latched as long as V
CC
stays
above the V
CC(reset)
threshold.
