Power supplies: lower volts, more intelligence

DN Staff

January 22, 2001

8 Min Read
Power supplies: lower volts, more intelligence

The general trend in electronics today is toward higher operating frequencies and smaller devices. To retain isolation between conductors packed closer together, small devices in turn call for lower voltages, and thus higher currents if the same power levels are maintained for the increased functionality often demanded by users, even in the face of better energy management.

We have a plan. The Power Sources Manufacturers Association (PSMA, Mendham, NJ) holds a "roadmap" conference every three years which brings together researchers, suppliers, manufacturers, and users to address technology trends. Last year's meeting spun off a follow-up session to explore problems with the high current, low voltage trend in semiconductor devices.

The chief concerns addressed at this meeting might be obvious to any engineer having studied basic circuit theory-as currents increase, the resistive power loss in a circuit goes up as the square of the current. Resistance between components must be driven down to avoid power losses and heat generation. If packaging volume were no concern, then conductors could just be made thicker to lower resistance.

In addition, at the higher frequencies devices are clocking at, inductive effects (proportional to the rate of change in current, di/dt) also increase noise, causing conductors to act as EMI-generating antennae-the longer the conductor the worse the offense. And with systems running at inherently lower voltages, any spikes in voltage from interference are that much more pronounced. Thus designers are looking to minimize the length of such conductors.

Integration of a dc power supplying voltage regulation module (VRM) with the microprocessor it powers cuts overall package size and EMI (due to short via runs), but taxes thermal managemetn because of component stacking which reduces exposed area. Such stacks, minus a heat sink, are on the order or 0.5 inch thick. The perforated magnetic layer acts as a coil to suppress inductive noise losses.

But according to PSMA Executive Director Joseph Horzepa, the latest conference highlighted the astute design of distributed power architecture (DPA) and point-of-load applications that have evolved to minimize such power losses and inductance effects. Many designers are now putting power converters or supplies closer to the devices they are feeding. For instance, a high voltage, low current ac-dc supply can feed a point-of-load dc-dc converter, which then steps the voltage down for the short run to the high-speed device. "Sometimes the final supply is right on the chip," notes Horzepa, "so there are no leads to generate interference." High voltage thus supplies a bus that feeds converters driving circuits at lower voltages and higher frequencies. The ultimate extension would be to integrate the supply with the load it is driving, he adds.

Batter(y) up! The use of batteries is booming, according to Norm Allen, president of PowerSmart (Shelton, CT), a Duracell spin off. The firm makes mixed-signal IC chips that are embedded in batteries. Recent rolling brownouts in California highlight the limits of the current power grid. "At around 8%, the Internet is the largest consumer of electric power in California. This includes data centers, and browser and server farms. Since no power stations are being added, there will be more power generation at sites, decentralizing the power grid. This will include banks of batteries for load leveling, starting, and uninterrupted power supplies (UPSs)," he says.

Designers of hand held and portable devices also have power (i.e. battery) issues related to the longevity of the supply before recharging or replacing is needed. Thus, efficient use of the energy available is paramount. Usually more efficient devices using the power are turned to, in order to husband batteries, but now at the supply end "smart battery" electronics have been developed.

Improved packaging, processing architectures, magnetic components, and thermal management have boosted power density in both dc-dc and ac-dc power suppies. The ac-driven devices are inherently larger because they need to contain input rectifiers, EMI filters and perhaps a processor for harmonic or power factor correction. Typical packages are about 1 1/2 inches square at the most.

Allen says, "Basically the smart battery chips contain battery-behavior models that predict performance for a certain condition. The IC outputs data on battery condition to a host processor, which reads it to do power management and diagnostics. A PC may run 30-40% longer using smart battery power management software." Here, smart features will balance demand needed by particular applications and also selectively shut down functions if the keyboard is not stroked over periods of time.

Allen offers this consideration for battery device designers: "If you want longer run time and have limited space and weight for a battery, you're going to need accurate control of it-or else your battery turns out too big or is not optimized to use the energy left in it."

The heat is on. While component integration is good for electrical performance, packing power conversion close to or on top of devices also leads to heat dissipation problems when that power is used. Chris Soule, an engineer and technical marketing manager for Aavid Thermalloy (Concord, NH), notes that thermal design should be considered at the concept stage of the design and must take into account how the user will use the system. He notes that the next few years should see cooling solutions that include "bigger, cost effective heat pipes, thermoelectric coolers, spot cooling using board-mounted refrigeration condensers, liquid baths and sealed enclosures, and cold forged, extruded aluminum heat sinks" (see Design News 1/8/01). Soule speculates that heat sinks and spreaders may eventually be integrated with active semiconductor components and passive devices (resistors, capacitors, and inductors) as well. Thus engineers, ever eager to have more ammunition, will have more arrows than ever to add to their current design quivers containing heat sinks, fans, and heat pipes.

Power supply providers, like other manufacturers, are learning to live in a worldwide marketplace. According to Joseph Horzepa, executive director of the multinational Power Sources Manufacturers Association (PSMA; Mendham, NJ), "Designers can be anywhere around the world designing products for anywhere else. And that product may be used in many or just a local market." He also notes that customers for power supplies "don't want to call around the world for a product that is typically only 4% the cost of the device it goes into." Users want localized availability and support. Thus, many manufacturers are setting up production lines around the world to more readily supply customers in a timely fashion.

To achieve shorter time to market and integrated design, Horzepa says that power supply electrical designers and packaging engineers are involved in concurrent design teams. And now process engineers are being added to such teams to ensure the design can be produced in a quality manner. "It is important that the walls between design disciplines become lower and lower. The trend for companies is to account for all design factors concurrently, and in the end, the big question is 'How much does it cost?'" he notes.

Horzepa also highlights the presence of PSMA on bodies that formulate international and local standards and testing practices. Thus, it is able to keep its members tightly in the loop on any regulatory-dictated design changes.

Integration cuts costs

Integration of power management onto a single IC cuts board space and production costs (due to a lower parts count, which simplifies assembly). As shown here, a single IC can control many components at differing voltages.

According to On Semiconductor (Phoenix, AZ) engineer and Technical Marketing Manger Randy Frank, whose company makes both integrated and distributed power supply systems, development costs are probably higher for the integrated design. Thus many companies will develop hand-held products using available, discrete off-the-shelf components, if they can, to have test products as soon as possible, cutting overall time to market. Later, full-production versions can then take advantage of integrated supplies. While flexibility for changes may be greater with several distributed components, Norm Allen, president of PowerSmart (Shelton, CT) notes that firmware (i.e. flash memory) and software are allowing increased flexibility in integrated supplies.

Frank adds that integrated power management in BiCMOS technology sees bipolar analog circuits integrated with CMOS logic capability, "allowing for a smoother interface with the microprocessor. Circuit protection schemes and error reporting functions can also be implemented within the power IC."

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