Primary-Side-Control for LEDs

Published:2012/3/5 0:52:00 Author:Ecco From:SeekIC

Monolithic Power Systems MP4021 power solution reduces component costs and improves overall energy efficiency with several methods，including the primary-side control. It also limits primary-side turn-on switching loss，using boundary conduction mode (BCM) and implements active power-factor correction (PFC).

The general illumination markets have been rising the demand for high-efficiency lighting with LEDs. Reducing up-front costs and improving overall energy efficiency are the new trend of the LEDs market. The MP4021’s primary-side control solution uses a proprietary real-current control method to accurately estimate the current through the transformer’s secondary side without additional circuitry. This method measures the current through the transformer’s primary-side with a sense resistor connected to the MOSFET. T he MP4021 utilizes BCM to improve power transfer from the AC source to the LED string while maintaining a near-constant output RMS current. BCM makes the transformer work on the boundary between the continuous and discontinuous mode, which is quite different from the well-known resonant converter and has several advantages in both energy efficiency and output noise. Unlike conventional fixed-frequency operation, the device uses a variable-frequency signal. This operation generates a constant turn-on time over each line half-cycle: The turn-off time is determined by the magnetizing energy discharged through the transformer to the load of the secondary-side.

The MP4021 also uses active PFC to help improve the power factor. The MP4021 not only simplifies the application circuit, but also has several protective features，including over-voltage protection; short-circuit protection, and over-temperature protection，in a compact SOIC8 package that provides designers with additional flexibility to engineer a safe and attractive luminaries for commercial, industrial, and the emerging residential lighting markets.

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