The medium size DirectFET is about the same size as the industry-standard PQFN but holds the same size die as the larger D-Pak. The large can DirectFET is about the same size as the D-Pak. It has a 60% smaller footprint than a D2Pak or 85% reduced volume but it holds a die that is 30% larger than a D2Pak. “You’re breaking this fundamental ratio between die size area and package footprint,” says Jackson. “This is what DirectFET does by eliminating these wire bonds and the leadframe.” The result is in a much lower RDS(on) in a given pcb area.

Figure 4. Compared to common SMT wire-bonded/leadframe packages, IR’s DirectFET has a smaller footprint yet higher performance. Select figure to enlarge.

Within the DirectFET2 platform, IR can optimize the silicon in one of three ways: (1) low RDS(on), (2) low Qg, or (3) logic-level operation. The three options provide flexibility to customize the silicon for customers’ specific needs. The AUIRF7739L2 is an example of optimizing for low RDS(on) and the AUIRF7665S2 is an example of optimizing for low Qg. IR plans to release eight more products in early 2010.

Solderable Front Metal IGBT

IR’s solderable front metal IGBTs introduced just a month earlier target inverter modules used in electric vehicles and hybrid electric vehicles. The AUIRG7CH80K6B-M is a 1200-V chip with SFM technology that also allows dual-sided cooling.  In addition to improved thermal performance, the solderable surface eliminates the need for wire bonds.  “With wire bonding in a module, you do take a yield hit and you do have a great cost hit if you have a yield problem because you have to throw away the whole module,” says Jackson.

High-Efficiency Audio

Efficient audio systems are among the more subtle approaches to reduce power consumption and make a vehicle more efficient. Although not designed specifically for the Volt, the Bose Energy Efficiency Series sound system is debuting in the Volt because General Motors’ engineers recognized the potential to improve the Volt’s all-electric range. “When you are making acoustic output, generally speakers and amplifiers are very inefficient,” says John Pelliccio, product planning manager, Automotive Systems at Bose Corporation.

Linear amplifiers usually run about 25% efficiency generating 1-W output for every 4 W they consume from the battery. Converting the electrical energy to cone motion in the speaker is very inefficient as well. “You have to pull a considerable amount of power from the battery in order to be able to make a sound system that is loud enough and powerful enough to overcome the wind noise and tire noise and give you the sort of concert-level volume that makes the music sound exciting,” says Pelliccio.

The Bose system that is going into the Volt is 30% smaller, 40% lighter and 50% more efficient than comparable automotive sound systems. “It actually uses about half the battery power that a regular sound system would use,” notes Pelliccio. “That is important in a car like the Volt because when you are talking about 40 miles of all-electric range, you want to be able to use every watt that you’ve got in that battery to move those tires a couple of revolutions forward.”

Since the system is proprietary, Bose engineers can’t say exactly what they are doing to improve the efficiency. However, the improvements are a combination of two aspects: Class D switching circuitry plus improved speaker design. “Class D audio will allow you to take that 25% efficiency that you get from the linear amplifier and move it into the 90 to 91% range,” says Pelliccio. Bose engineers worked on the magnetics of the speaker design to make the speaker much more efficient creating high motor force drivers. “We are taking the energy that is being very efficiently produced by the amplifier, and we are turning it into power that is being pushed out very efficiently by the speakers,” he explains.

The Bose speakers use neodymium instead of traditional ferrites so they are lighter, smaller and utilize the amplifier power more efficiently — users get a double benefit. “What Chevy [engineers] computed is that having that system in the car is the equivalent of shaving out about 50 pounds of mass,” says Pelliccio.

Headlamp LEDs

LED technology has found widespread acceptance in vehicles for interior and taillight applications. One of the highest energy savings can occur in headlights. The 2011 Audi A8 uses Osram’s OSTAR LED technology (Fig. 5). The OSTAR headlamp is a new product platform with up to five LED chips. Typical light values are 160 lm at 700 mA for each LED chip but values between 125 lm and 1100 lm are easily achieved. The easily controlled LEDs provide high and low beams as well as cornering lights, fog-lamps and daytime running lights. In addition to the reduced lighting power consumption, the LEDs can eliminate the need for a mechanical cornering systems used for conventional headlamps saving both weight and cost.

Turning on Less Power

Figure 5. While achieving a unique appearance in its headlight design, the 2011 Audi A8 uses Osram’s OSTAR LED platform to reduce power consumption. Select figure to enlarge.

Since adding more and more electronics has become a way of life for automakers, more efficiently controlling the power consumed by the loads and systems has also become a way of life for suppliers. Power semiconductors provide a starting point for more efficiently switching power. With more efficient techniques to reduce the loads such as LEDs and audio system design, the industry can continue to use 14 V for hotel loads and avoid higher voltage alternatives, such as 42 V, that were predicted over a decade ago.

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