March of the Power Supplies

Jan. 1, 2007
Power supplies, marching from the obscure corners of the systems, are spreading onto the circuit boards and taking their place near the devices they power.

Power supplies, marching from the obscure corners of the systems, are spreading onto the circuit boards and taking their place near the devices they power. However, this migration has not been an easy one; in fact, system designers have fought it every step of the way.

From the early days when lead-acid batteries powered the old electromechanical systems until the early 1980s, power conversion, with its inherent electrical noise, was considered dirty. Power supplies were to be buried somewhere at the bottom of the system, just like the dirty boiler for steam heating a building is always located tucked away in the basement.

In those days, no self-respecting system designer wanted the power supply placed on his pristine circuit board. It was enough to deliver the voltages and the currents to the front-door pc-board connector. As IC manufacturers piled more and more circuits on ever-smaller dies, the “fences” between the active circuits forced the manufacturing process to shrink from tens of microns to tens of nanometers.

To reduce the migration of electrons over the borders, the operating voltages decreased from the long-standing standard of 5 V to sub 1-V levels. Clock speeds increased from tens of megahertz to multiple gigahertz ranges that require higher currents. The two forces of lower voltages and higher currents combined as though creating a powerful magnetic field that would shrink the space between the ICs and power supplies.

Initially, distributed power architecture (DPA), with just a limited number of on-board voltages, used several large isolated converters aptly named “bricks” to provide the voltages required by the ICs. But as the number of different voltages increased, a single efficient isolated converter, commonly called a “dc-dc transformer,” replaced the many bricks to provide isolation and an intermediate bus voltage for multiple nonisolated point-of-load converters (POLs) next to the ICs.

Today, with even more voltages appearing on pc boards, there is an increasing need to manage the operation of each individual POL. Solving this need by adding external management circuitry around the analog POLs only increases the complexity and the circuit board territory occupied by power conversion and management.

Digital power conversion provides the needed solution by replacing fixed analog circuitry with digitally programmable devices — controlled and configured using only one or two serial communications buses with a commonly accepted I2C protocol. By having a single device that can be software programmed and configured to look like almost any analog POL on the market, digital programming provides additional benefits by reducing the number of different models a manufacturer has to produce and inventory.

As the need for tighter and tighter power control of various circuits on the IC die increases, the next migratory step for power conversion will be to cross the IC border. Just as POLs in the past moved onto the circuit board, power converters will move onto the ICs. Proliferation of voltages and the associated requirements of managing them will increase the number of required converters where each converter, integrated inside the IC, will provide only a small portion of the overall power.

Higher switching frequencies require smaller inductors and capacitors, while the decreasing power requirements of each individual switching device enables their integration into the same IC process. Several patents for the thermoelectric cooling mechanisms, placed on the opposite side of the same wafer, already exist.

One might argue that with power problems already plaguing ICs and microprocessors, who needs another hot component to add to the IC fire?

The same argument given for the migration of power from the system to the circuit board can be used for the migration of power conversion onto the IC. We hear that no self-respecting IC designer wants the noisy and hot power converter sharing the spotless digital circuits on his IC. Where did we hear this before? The question in my mind is not if this will happen, but when will it happen?

Lou Pechi's love of electronics has led him through a 45-year career in engineering, technical sales and marketing. As an engineer, Pechi developed power supplies, audio warning voice annunciators, automatic test equipment and underwater communications spectrum-analysis systems. Following that experience, Pechi managed sales and marketing for several major power-supply companies. At Power-One, Pechi introduced the Modular High Power product family, and he was also instrumental in the establishment of Power-One's Silicon Power Systems (SPS) division.

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