National Semiconductor Intros LM5021 AC-DC PWM Controller
National Semiconductor Corp. (Santa Clara, CA) introduced its new LM5021, a high-performance, ac-dc pulse-width-modulation (PWM), current-mode controller that is designed to save energy in power supplies. The LM5021 contains all the features needed to design energy-efficient, 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, and utilizes a cycle-skipping burst mode during standby or light-load operations to reduce power losses. The 25 µA startup mode minimizes 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 under-voltage lockout's wide hysteresis allows designers to select a smaller bias supply filter capacitor. The LM5021 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 startup surge currents that can stress components or saturate the power transformer.
The LM5021 is available in an 80% version for flyback converters and a 50% version for forward converters, distinguished by the maximum duty cycle of the pulse-width modulator. Available now in MSOP-8 and MDIP-8 packages, the LM5021 is priced at $0.45 each in 1,000-unit quantities. All packages are available lead-free.
