The NCP1361/66 offers a new solution targeting output power
levels from a few watts up to 20 W in a universal−mains flyback
application. Due to a novel method this new controller offers a
primary−side constant current control, saving secondary−side
components to perform current regulation.
The NCP1361/66 operates in valley−lockout quasi−resonant peak
current mode control mode at nominal load to provide high efficiency.
When the secondary−side power starts diminishing, the switching
frequency naturally increases until a voltage−controlled oscillator
(VCO) takes the lead, synchronizing the MOSFET turn−on in a
drain−source voltage valley. The frequency is thus reduced by
stepping into successive valleys until the number 4 is reached. Beyond
this point, the frequency is linearly decreased in valley−switching
mode until a minimum is hit. Valley lockout during the first four
drain−source valleys prevents erratic discrete jumps and provides
good efficiency in lighter load situations.

Features
• ±10% Current Regulation
• 560 V Startup Current Source
• No Frequency Clamp, 80 or 110 kHz Maximum Switching
Frequency Options
• Quasi−Resonant Operation with Valley Switching
Operation
• Fixed Peak Current & Deep Frequency Foldback @
Light Load Operation.
• External Constant Voltage Feedback Adjustment
• Cycle by Cycle Peak Current Limit
• Built−In Soft−Start
• Over & Under Output Voltage Protection
• Wide Operation VCC Range (up to 28 V)
• Low Start−up Current (2.5 A typ.) with NCP1361
• Clamped Gate−drive Output for MOSFET
• CS & Vs/ZCD pin Short and Open Protection
• Internal Temperature Shutdown
• Less than 30 mW No−Load Performance at High Line
with NCP1366 Version
• These are Pb−Free Devices

Typical Applications
• Low power ac−dc Adapters for Chargers
• Ac−dc USB chargers for Cell Phones, Tablets and Cameras