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National Semiconductor Introduces Energy-Efficient, Integrated AC-DC PWM Controller For Power Systems

LM5021 Features Skip, Burst and Ultra-low Power Bias Circuitry for Improved Efficiency Over a Wide Load Range

Jun 1, 2005

June 1, 2005 - National Semiconductor Corporation (NYSE:NSM), a world leader in power management technology, today introduced a high-performance AC-DC pulse-width-modulation (PWM) current-mode controller that is designed to save energy in power supplies.  This device 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, 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 minimizes power loss and saves space, allowing the designer to use a small, low-power resistor.

“Energy efficiency is more important today than ever, with legislation and advisory standards on standby power developing worldwide. National’s integrated LM5021 PWM controller offers designers of AC-DC power converters the right combination of performance, space savings, comprehensive protection and lower heat dissipation to reliably meet the new energy standards,” said Paul Greenland, director of product marketing for National Semiconductor’s Power Management group. “The LM5021 also complements National’s LM5000 family of high-voltage isolated DC-DC PWM controllers and drivers, enabling our customers to design complete power systems from the AC line cord to the point of load.”

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.  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 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.

Additional Features and Benefits

  • Current-mode control provides improved line transient rejection and simplifies loop compensation.
  • Internal slope compensation prevents sub-harmonic oscillation at duty cycles greater than 50 percent.
  • Switching frequency is programmed by a single resistor and can be synchronized to an external clock to reduce interference.  
  • Internal leading-edge blanking of the current sense signal reduces external filtering.
  • Cycle-by-cycle current limiting prevents excessive currents during short circuit or overload
  • Programmable hiccup-mode over-load protection eliminates over-heating and reduces power consumption during over-load conditions.

Pricing and Availability
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.  More information about the LM5021 is available at http://www.national.com/pf/LM/LM5021.html
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Note to editors: A high-resolution downloadable photo of the LM5021 is available on National's photo gallery at http://www.national.com/company/pressroom/gallery/power.html.

About National’s Power Management Products
National Semiconductor is the number one supplier of power management ICs with 14.1 percent market share, according to iSuppli’s 2005 voltage regulator/reference survey.  National’s power management revenue grew 37.3 percent in 2004 over the previous year, compared to 24 percent growth for the industry during the same time period.  National's innovative power management products include best-in-class linear regulators; power monitoring, control and reference ICs; and switching converters, such as high-voltage ICs for DC/DC conversion, switched capacitor converters, lighting management ICs and inductive switching converters.  National's WEBENCH® online design tool allows designers to select a power management product, create and analyze a design, and then build custom prototypes that can be delivered within 24 hours.  More information about National’s power management products is available at http://power.national.com
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About National Semiconductor
National Semiconductor, the industry's premier analog company, creates high-performance analog devices and subsystems.  National's leading-edge products include power management circuits, display drivers, audio and operational amplifiers, communication interface products and data conversion solutions. National's key markets include wireless handsets, displays and laptops.  The company's analog products are also optimized for numerous applications in a variety of electronics markets, including medical, automotive, industrial, and test and measurement.  Headquartered in Santa Clara, California, National reported sales of $1.98 billion for fiscal 2004, which ended May 30, 2004.  Additional company and product information is available at www.national.com.