Lithium Technology Meets Challenge of Greater Efficiency in Smaller Package

Power sources include the ac-to-dc and dc-to-dc converters that make the proper voltages and power levels available in portable and stationary electronic products. The integrated circuits (ICs) for these products are being challenged to provide greater efficiency in the same or smaller packages and, at the same, even greater functionality. Alternative battery technologies and energy sources such as fuel cells and energy harvesting are generating a lot of interest.

While the iPhone may be the hottest new battery-powered product of 2007, it only works when it has sufficient power to operate. It does not have a second battery option. To provide an alternative to wall charging, Medis 24/7 power pack is a disposable fuel cell charger. Direct Liquid Fuel Cell (DLFC) technology provides up to three months or 30 hours of mobile charging.

Getting the most out of lithium-ion powered portable devices requires higher efficiency and improved power management techniques. For example, ROHM's BD8611EFV integrated circuit (IC) provides six-channels for power management. In addition to several protective functions for various power supply failures, the unit has a special startup sequence for properly powering up different voltage sections, such as the DSP (3.3V) and I/O (1.8V).

Building on its current market acceptance, lithium-ion battery technology is providing a basis for future battery developments. Jeff Shepard, president, Darnell Group, a power electronics strategic information company, notes the emergence of thin-film lithium-ion batteries to achieve smaller form factors than today's lithium-ion units. "There are a couple of companies already shipping thin-film batteries," says Shepard. The batteries are for wireless sensor networks and lower power applications.

In some instances, these batteries will be used in locations where they cannot be recharged by traditional techniques. One of the alternatives is energy harvesting technology.

In the area of dc-to-dc converters, one of the trends Shepard projects is higher power from IC converters. "We see IC converters moving up in power quite a bit," says Shepard. "The sweet spot was about 1A, today it is between 1 and 3A and in the future, we see it moving up over 3A."

Shepard also notes the need for higher efficiency in ac-to-dc converters. "The biggest trend in ac-to-dc converters is going to be digital control and improved efficiency and a flat load curve where you have 80 percent efficiency from 20 percent load up to 90 percent load or more," says Shepard.

Available today in a 1 x 1.35 timesx .50-inch form factor, Bias Power's BPS-2 provides a micro-size ac-to-dc switching power supply that operates from an 85 to 265V ac and provides a single or dual output with conversion efficiency up to 75 percent.

Rugged Power

One of the more common trends in many products is greater ruggedness. For power supplies, this can mean an extended operating range or improved ability to withstand faults. In either case, it can avoid increasing the size. For example, Kepco Inc.'s 1200 KLP power supplies provide an additional operating region in both higher current and higher voltage ranges compared to typical laboratory grade supplies. Automatically recalculating voltage/current limits forms a constant-power hyperbolic-shaped boundary between the voltage and current modes. For the 1,200W unit, this means full power over the entire operating range instead of a single maximum power operating point.

According to Saul Kupferberg, Kepco's vice-president of sales/marketing, the hyperbolic power limit is certainly unique in Kepco's product line and possibly the industry. The newest aspect in 1.2K models is built-in General Purpose Interface Bus (GPIB) and LAN interfaces. The LXI-approved Ethernet-based LAN interface allows multiple-user access via a standard Web browser.

Improved fault protection schemes can also increase the power supply's ruggedness factor and possibly avoid increasing the size of the unit to survive some level of faults. Applied Power Systems SixPac high-power inverters provide advanced integrated fault protection features that allow safe operation in demanding environments. The IAPL2800B120 extends the power range up to 2,800A peak current capacity. Available in both air and liquid cooled versions, the units use isolated and scaled analog feedback of critical operating parameters, such as dc bus voltage, output current and heatsink temperature for implementing the protection.

This section will look closer at current trends in dc-to-dc converters and batteries.