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Full-bridge PWM controllers achieve impressive efficiency

Full-bridge PWM controllers achieve impressive efficiency

National Semiconductor Corp. introduces full-bridge pulse width modulation (PWM) controllers that integrate all four primary-side bridge MOSFET gate drivers. The LM5045 and LM5046 are well suited for delivering higher efficiency and higher power density in quarter-brick and eighth-brick power modules used in a variety of high input voltage communications infrastructure applications.

As members of National’s PowerWise energy-efficient product family, the LM5045 and LM5046 PWM controllers ease the design of full-bridge topology-based power converters into small form factor power supplies by reducing the number of external power components needed with existing full-bridge solutions. Watch a phase-shifted full-bridge demonstration featuring the LM5046 here.

The LM5045 PWM controller contains all of the features necessary to implement a conventional full-bridge topology power converter using either current mode or voltage mode control. For applications requiring zero-voltage switching (ZVS) to minimize electromagnetic interference (EMI) due to switching noise, the LM5046 PWM controller contains all the features necessary to implement a phase-shifted full-bridge topology.

Offered in small, thermally enhanced 5.0 x 5.0 x 0.8 mm LLP and 4.4 x 9.7 x 0.9 mm TSSOP packages, the full-bridge controllers operate on the primary side of an isolated dc-dc converter with input voltage up to 100 V. These highly integrated controllers provide robust 2-A high and low-side gate drivers for the four external bridge MOSFETs in addition to the control signals for the secondary side synchronous rectifier MOSFETs and an internal high voltage start-up regulator.

Intelligent startup of the synchronous rectifiers (SR) allows monotonic turn-on of the power converter, even with pre-bias load conditions. The synchronous rectifier control signals offer independent and programmable leading/trailing edge dead-times between the primary and secondary MOSFET control signals for optimizing efficiency, and the SR signals are limited to 5 V for use with digital isolators. Additional features include dual mode over-current protection featuring both cycle-by-cycle current limiting and hiccup mode restart, programmable soft-start, timing for both primary and synchronous rectifiers, programmable line UVLO and OVP, a synchronizable 2 MHz oscillator and thermal shutdown.

National’s new LM5045 and LM5046, together with secondary side FET drivers such as the LM5110, LM5111, and LM5112, provide a complete controller solution to implement a highly efficient, small form factor full-bridge power converter.

For more information, contact National Semiconductor Corp., 3689 Kifer Road, Santa Clara, CA 95051. Phone: (800) 272-9959.

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