MC33262PG

The MC33262PG from onsemi is an active power factor correction controller specifically designed for use as a pre-converter in electronic ballast and off-line power converter applications. Operating in critical conduction mode (CRM), also known as transition mode or boundary conduction mode, the device ensures near-unity power factor by forcing the boost inductor current to return to zero before each new switching cycle begins. The MC33262PG integrates all essential PFC control functions into an 8-pin package. Key building blocks include a one-quadrant multiplier that forces the input current waveform to follow the rectified AC line voltage, a transconductance error amplifier for output voltage regulation with a trimmed 2% bandgap reference, a zero current detector that triggers the next MOSFET on-cycle when the inductor current reaches zero, and a current sense comparator for cycle-by-cycle peak current limiting. Protection features include an overvoltage comparator that eliminates runaway output voltage when the load is suddenly removed, undervoltage lockout (UVLO) with 6V hysteresis that ensures reliable startup at 13V and shutdown at 7V, and a multiplier output clamp that limits maximum peak switch current. The totem-pole output can source or sink 500mA for direct MOSFET drive, with a high-state clamp protecting the MOSFET gate from overvoltage. The low 250uA startup current allows efficient self-powered operation from the high-voltage bus through a series resistor.

The MC33262PG operates as a critical conduction mode (CRM) boost PFC controller. Key subsystems include: (1) Multiplier – the one-quadrant multiplier combines the rectified AC line voltage sense signal (Pin 3) with the error amplifier output (Pin 2) to generate a current reference that follows the line voltage waveform; this ensures the input current tracks the AC voltage for near-unity power factor; (2) Zero Current Detector – monitors the boost inductor voltage via an auxiliary winding (Pin 5); when the inductor current reaches zero, the diode voltage reverses, and the zero current detector triggers the MOSFET to turn on again; this variable-frequency CRM operation naturally achieves discontinuous input current; (3) Error Amplifier – a transconductance amplifier (Pin 1 output, Pin 2 inverting input) regulates the boost output voltage to the setpoint defined by the 2.5V bandgap reference; an external compensation network at Pin 2 provides loop stability; (4) Current Sense Comparator – compares the MOSFET current sense voltage (Pin 4) with the multiplier output; when peak current reaches the reference level, the MOSFET is turned off; cycle-by-cycle limiting ensures safe operation; (5) Overvoltage Protection – an OVP comparator monitors the feedback pin; if the output voltage exceeds approximately 106% of setpoint due to load removal, the drive output is disabled to prevent runaway; (6) Startup Timer – an internal timer provides periodic drive pulses during startup to charge the VCC supply from the bootstrap resistor, allowing the device to self-start without auxiliary supply.

• Offline boost PFC: 85-265VAC input to 400VDC bus for ATX/server power supplies
• Electronic ballast: PFC pre-regulator for fluorescent and HID lighting
• Industrial power supply: 100W-500W PFC front-end for 24V/48V output converters
• Appliance power supply: PFC pre-converter for white goods and HVAC
• Laptop adapter: 75W-120W PFC for universal input adapters