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.
The LM5021 is available in two versions, distinguished by the maximum duty cycle of the pulse-width modulator: 80 percent and 50 percent, catering for flyback and forward converters, respectively.
Available now in MSOP-8 and MDIP-8 packages, the LM5021 is priced at 45 cents each in 1,000-unit quantities. All packages are available lead-free.