11 July 2017

Quasi-Resonant Switching Power Supply ICs

Here is a look back of the LC5500 series, a Sanken product, that acts as a switching power supply IC using quasi-resonant topology.


This device is intended to be employed for input capacitorless applications, and making it possible for systems to comply with the harmonics standard (IEC61000-3-2 class C). It incorporates separate controller and power MOSFET chips.

The controller adapts the average current control method for realizing high power factors, and the quasi-resonant topology contributes to high efficiency and low EMI noise. The series is housed in either DIP8 or TO-220F-7L (Sanken designator: FMY207) packages, depending on output power capability. The rich set of protection features helps to realize low component counts, and high performance-to-cost power supply.


DIP8 package (LC551xD/LC552xD) and TO-220F-7L package (LC5523F)

Integrated on-width control circuit (it realizes high power factor by average current control)

Integrated startup circuit (no external startup circuit necessary)

Integrated soft-start circuit (reduces power stress during start-up on the incorporated power MOSFETand output diode)

Integrated bias assist circuit (improves the startup performance, suppresses VCC voltage droop during operation, allows reduction of VCC capacitor value as well as use of a ceramic capacitor)

Integrated Leading Edge Blanking (LEB) circuit

Integrated maximum on-time limit circuit

Dual-chip structure, with an avalanche-guaranteed power

MOSFET (allows simplified surge suppressing circuits)

Protection features:

-Overcurrent protection (OCP): pulse-by-pulse

-Overvoltage protection (OVP): intermittent oscillation operation

-OVP-activating pins vary by product series

-Overload protection (OLP): intermittent oscillation operation

-Thermal shutdown (TSD): halts switching operation and latches in the off-state


Source : Allegro MicroSystems


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