onsemi ML4801IS

The ML4801 is a controller for power factor corrected, switched mode power supplies. Key features of this combined PFC and PWM controller are low start-up and operating currents. Power Factor Correction (PFC) allows the use of smaller, lower cost bulk capacitors, reduces power line loading and stress on the switching FETs, and results in a power supply that fully complies with IEC1000-3-2 specifications. The ML4801 includes circuits for the implementation of a leading edge, average current “boost” type power factor correction and a trailing edge pulse width modulator (PWM).

The PFC frequency of the ML4801 is automatically set at half that of the PWM frequency generated by the internal oscillator. This technique allows the user to design with smaller output components while maintaining the optimum operating frequency for the PFC. An over-voltage comparator shuts down the PFC section in the event of a sudden decrease in load. The PFC section also includes peak current limiting and input voltage brown-out protection.

The ML4801 consists of a combined average-current controlled, continuous boost Power Factor Corrector (PFC) front end and a synchronized Pulse Width Modulator (PWM) back end. It is distinguished from earlier combo controllers by its dramatically reduced start-up and operating currents. The PWM section is intended to be used in current mode. The PWM stage uses conventional trailing-edge duty cycle modulation, while the PFC uses leading-edge modulation. This patented leading/trailing edge modulation technique results in a higher useable PFC error amplifier bandwidth, and can significantly reduce the size of the PFC DC buss capacitor.

The synchronization of the PWM with the PFC simplifies the PWM compensation due to the reduced ripple on the PFC output capacitor (the PWM input capacitor). The PWM section of the ML4801 runs at twice the frequency of the PFC, which allows the use of smaller PWM output magnetics and filter capacitors while holding down the losses in the PFC stage power components.

In addition to power factor correction, a number of protection features have been built into the ML4801. These include soft-start, PFC over-voltage protection, peak current limiting, brown-out protection, duty cycle limit, and undervoltage lockout.

• Internally synchronized PFC and PWM in one IC
• Low start-up current (200μA typ.)
• Low operating current (5.5mA typ.)
• Low total harmonic distortion
• Reduces ripple current in the storage capacitor between the PFC and PWM sections
• Average current continuous boost leading edge PFC
• High efficiency trailing edge PWM optimized for current mode operation
• Current fed gain modulator for improved noise immunity
• Brown-out control, overvoltage protection, UVLO, and soft start