NCL2801CDBDR2G

The 8−pin PFC controller NCL2801 is designed to drive PFC boost stages. It is based on an innovative Valley Count Frequency Fold−back (VCFF) method. The circuit classically operates in Critical conduction Mode (CrM) for high load values. When the load decreases a Discontinuous Conduction Mode DCM is forced by forcing a dead time which, by construction corresponds to a fixed number of valleys. The lower the output power, the higher the number of valleys corresponding to the dead time. After DCM works down to 6th valley switching and if the load continues to decrease, a dead time is continuously added to the 6th valley. The end of additional dead time is synchronized with the drain voltage valley. The maximum switching period is limited to 36.5 μs. VCFF maximizes the efficiency during DCM and light load. In particular, the stand−by losses are reduced to a minimum. Like in FCCrM controllers, internal circuitry allows near−unity power factor even when the switching frequency is reduced. Housed in a SO−8 package, the circuit also incorporates the features necessary for robust and compact PFC stages, with few external components.

Applications

• PC Power Supplies
• Lighting Ballasts (LED, Fluorescent)
• Flat TV
• All Off Line Appliances Requiring Power Factor Correction

Key features

• Near−Unity Power Factor
• Critical Conduction Mode (CrM)
• Valley Count Frequency Fold−Back (VCFF)
• Peak Current Control Mode to Maintain a Proper Current Shaping in VCFF Mode
• Fast Line / Load Transient Compensation (Dynamic Response Enhancer) Option
• Brown−out Detection
• Two−level Line Feed−Forward (HL&LL)
• Valley Turn−on (No Valley Hoping by Construction)
• High Drive Capability: -500 mA / +800 mA
• VCC Range: from 10.5 V to 27 V
• Low Start−up Consumption for:
• [*C*] & [*D*] Option: Low VCC Start−up Level (12.5 V) [*A*] & [*B*] Option: High VCC Start−up Level (17.0 V) [*E*] & [*F*] Option: High VCC Start−up Level (10.5 V)
• This is a Pb−Free Device
• Thermal Shutdown
• Non−latching, Over−Voltage Protection (3 Prog Levels)
• Over Current Limitation
• Low Duty−Cycle Operation if the Bypass Diode is Shorted
• Open Ground Pin Fault Monitoring
• Pin CS shorted to GND or open Monitoring
• Pin ZCD open tested before controller starts
• Controller not allowed to start if MULT pin is left open