AC-DC PWM controller

National Semiconductor has introduced a high-performance AC-DC pulse-width-modulation (PWM) current-mode controller that is designed to save energy in power supplies.

The device contains all the features needed to design single-ended flyback and forward AC-DC converters for telecommunications, networking equipment power systems, and high-end industrial and consumer power supplies.

The LM5021 PWM controller is energy-efficient at light loads, satisfying energy conservation standards being implemented worldwide. It also utilizes a cycle-skipping burst mode during standby or light-load operations to reduce power losses. The low 25 micro-amp start-up mode also minimises power loss and saves space, allowing the designer to use a small, low-power resistor.

The chip integrates a high-frequency current-mode PWM controller with internal slope compensation, as well as a user-programmable soft-start and a 0.7 A peak MOSFET driver. The undervoltage lockout’s wide hysteresis allows designers to select a smaller bias supply filter capacitor, saving money and board space.

It also has cycle-by-cycle current limiting and hiccup-mode overload protection, protecting against secondary short circuits and sustained operation above the power limit. The built-in soft-start timer allows the designer to minimize start-up surge currents that can stress components or saturate the power transformer.