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Controller for forward active clamp reset converters

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article image Includes a high-frequency oscillator.

NATIONAL Semiconductor Corporation, represented by Arrow Electronics Australia Pty Ltd , has increased its family of single and dual forward active clamp pulse-width modulation (PWM) controllers with the introduction of the LM5026.

It is an integrated, 100V forward active clamp reset PWM controller that uses current-mode control.

This controller is designed for high switching frequencies and provides improved efficiencies and power densities compared to conventional forward converters.

It is well-suited for communication system dc-dc and ac-dc power conversion, as well as industrial power systems, including single- and multi-output industrial power supplies.

The LM5026 provides an array of features and flexibility that reduces the complexity and cost of external parts. It enables designers to implement power converters using the active clamp reset technique with peak current-mode control.

Active clamp reset is one of the most popular single-ended topologies for isolated dc-dc converters in distributed power architectures. It supports operation at duty cycles above 50% to efficiently deliver fixed, regulated output from a widely varying input supply.

The LM5026 is a fully integrated PWM control system that includes a high-frequency oscillator, current-mode PWM control circuitry and two power MOSFET drivers for reduced component count and quick implementation of efficient forward active clamp converters.

The integrated 3A main MOSFET driver and 1A clamp MOSFET driver improve system efficiency and speed, eliminating the need for external drivers.

The programmable, line-voltage-dependent, maximum-duty-cycle clamp minimises voltage stress, reducing power MOSFET cost.

In addition, the unique current-mode feedback of the LM5026 increases the effective bandwidth of conventional opto-couplers to simplify compensation and improve overall loop bandwidth and transient response.

The LM5026 features an integrated, wide-range input start-up regulator that operates between 13V and 100V, eliminating the need for external start-up regulator components.

User-programmable under-voltage lockout and soft-start circuitry provides customers with the flexibility to control power-on sequencing and minimise start-up surge currents, while the programmable restart circuit supports three modes of over-current fault protection.

The LM5026 also includes oscillator synchronisation circuitry that allows users to control electromagnetic interference by locking the PWM controller to an external master clock.

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