National releases Powerwise reference standards

National Semiconductor has released six new Powerwise reference designs that enable design engineers to deliver products that consume less power, extend battery life and generate less heat.

Powerwise reference designs combine energy efficient devices and arrange them in a system to actively lower power consumption and reduce heat dissipation.

Each proven Powerwise reference file kit includes applicable design schematic, bill of materials (BOM), board layout, firmware, design documentation and field-programmable gate array (FPGA) source code in synthesisable Verilog or VHDL.

The designs address a range of applications including portable, lighting, solar, industrial, medical, communications infrastructure, and test and measurement.

Engineers can increase the efficiency of harvesting solar power from photovoltaic cells with this reference design that efficiently converts sunlight into a charge current for lead acid batteries.

The design also compensates for variations in temperature and the amount of sunlight, maintaining the most efficient conversion throughout changing conditions.

The two-stage design monitors the solar panel voltages using a SEPIC design that provides the output voltage and tracks the input solar panel voltage over temperature, while the second stage takes the output of the first stage and boosts the input voltage.

Featuring Powerwise power converters, battery charging circuitry, audio drivers and display interface circuits, this reference design lets engineers initiate a power-saving mode when the portable media player (PMP) is unplugged from the wall power, automatically reducing the maximum brightness of the display as well as the output power of the audio drivers.

This reference design replaces backlight cold-cathode fluorescent (CCFL) tubes with strings of light-emitting diodes (LEDs) for lower power consumption, better durability, smaller size and brighter light that is more easily custom tailored to compensate for changes in ambient light.

Using a three-channel, constant-current LED driver with two strings of six series-connected LEDs, the design configures the LED driver as a boost converter to generate 21V to 27V output voltage with a 12V power source.

The design also includes a circuit utilising a photodiode to make the brightness of the display proportional to ambient light.

This improves the display's readability under all lighting conditions.

This reference design automatically adjusts display brightness for changing ambient light conditions to provide a more viewable display with better contrast.

The pulse-width modulation (PWM) dimming technique of National's LED driver dims or brightens the display backlight in response to ambient light condition.

This increases battery life and improves the visibility of the display under different viewing conditions.

A photodiode circuit measures ambient light and provides a signal for dimming the LEDs.

National collaborated with Avnet to develop a comprehensive reference design that implements high-speed, power-saving serial data interfacing for low-cost Xilinx Spartan-3 field-programmable gate arrays (FPGAs).

National's FPGA-Link SerDes combines high-speed data transfer flexibility with features such as automatic power down on loss of cable or input signal.

The included FPGA firmware monitors this cable/signal loss indicator from the SerDes to turn off unnecessary system logic and other external components for a significant savings in total power.

To help reduce wasted energy from inefficient AC/DC wall adapters that continue to run even without a load, this reference design uses switched-mode power supply (SMPS) technology in place of linear regulators to drastically improve conversion efficiency.

Additional circuitry 'wakes up' the power supply only when a load is applied, reducing losses to tens of milliwatts.

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