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Low voltage is sexy, but high voltage is reality

Low-voltage operation is increasingly becoming a driving factor in component design. The days of bipolar 15-V suppliers are gone, sliding down to 12 , 5 , 3 and now 1 V, operation, usually unipolar.

It's all about reducing power dissipation. A friend told me about a processor IC he is using that has over a dozen distinct power rails, at nominal voltages between 1 and 3 V, and with different tolerances. The CPU's designer wants to hit that elusive sweet spot of minimum power consumption and maximum performance. So what if the processor is surrounded by a forest of small regulator ICs to support these rails? Sorry, that's not his problem, it's your problem as the system designer.

(I wonder if the analog vendors have infiltrated moles into the digital-IC companies, in a far-sighted and clever move. These moles would insist on using as many distinct rails as possible, thereby driving the supply IC business. If Microsoft's ever-growing software OS footprint can drive PC's RAM and disk size, this could happen, too!)

Despite all the low-voltage talk, there's a little secret that the analog and power-supply companies know: higher voltages are alive and very well. Look at their recent products and you'll see many parts with double-digit input- and output-voltages ratings. These aren't for specialty items such as X-ray tubes, which require hundreds of volts, albeit at low current. These are for supplies in the 10-to-100 V range, delivering several amps.

Why is this? As usual, it's the physical reality that defines the analog world. On the input side, you may want to operate from an auto battery (12 V nominal, often higher) or a 48-V telco supply. On the output (load) side, doing real work takes power. Two simple equations say it all: P = V x I, and V = I x R. Large IR loss in the line, due to high currents, is a waste of power; heavier, lower-loss conductors are an expensive solution.

Who needs power? Consider Power over Ethernet (PoE) for a video camera. No problem, power levels are modest. But suppose you also need to power the camera's pan, zoom, and tilt (PZT) motors. The occasional power demands of the PZT function are far greater than the camera's. Similarly, a single PoE phone is a modest load, while an office full of them is not, and supplying a car's 5- to 10-kW demand from 12 V is a real struggle; so automakers have looked at 42-V systems.

Engineers know that the most efficient way to deliver power is to keep the voltage high and the current low. Power engineers have known this for over a hundred years; that's why they keep raising the voltages on their transmission lines. The laws of electricity which made them do it make us do it, too. Analog IC vendors know this reality, and that's why they are investing heavily in higher-voltage processes and designs despite all the 1-V news.

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