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3-Phase Power: Pavarotti, Choir Boys and Balloons
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Date 18 July 2002
Author Sean Hershberger

3-Phase Power

Editor's note: This was originally sent to me in an email in response to my comments about "3-phase power solution" in motherboard reviews. Lots of motherboard manufacturers use this technology as a selling point, but I wasn't sure exactly what it meant. I thought Sean's comments were worthy of making into an article as there's a lot of confusion about this topic. Thanks, Sean! -- Agg

What "three phase" power is referring to in this case, is a switching voltage regulator, which switches power in three phases.

Today's motherboards require all kinds of different "DC" Voltages. To get these different voltages, switching voltage regulators are used because they can be made very efficient.

Switching supplies work by taking chunks of power from one voltage source and providing it to hardware at a different voltage. The differences in the input and output voltage aren't of much interest here. The interesting issue is that the power is transferred from source to destination in chunks. By analogy:

Imagine your MB runs on air and has an air intake hose. You put air into the intake and the MB keeps draining it out. To keep it running, you have to keep the pressure in the hose, higher than atmospheric pressure. A single phase switching power supply would handle it as follows. You take a big guy (say Pavarotti) with a big balloon. He blows up the ballon while keeping the hose end closed. Then he attaches the balloon to the intake of the hose and lets the air drain in. Then he blows up the balloon with the hose end closed again... over and over and over.

Now it might occur to you that this is an awfully lumpy way to provide power. You'd be right. Another part of the picture is another balloon attached to your motherboard. The purpose of this balloon is to hold a reservoir of air (power) and smooth out fluctuations in incoming power. (As well as fluctuation due to the MB drawing different amounts at different times.) So when Pavarotti is busy blowing up his balloon, the balloon on the MB is getting smaller. When Pavarotti attaches his balloon to the hose intake, his balloon gets smaller, but the one on the MB gets bigger. (The balloons on the MB are known as Capacitors) The bigger the balloon on the MB is the smoother the power is. (Same goes for the amount of Capacitance on the MB.) As you might notice, there is "all kinds of AC weirdness going on" regardless of whether a MB has a "3-phase power solution".

So what about three phase power? Pavarotti is big and expensive and a rather lumpy source of air pressure. Plus with modern technology we can use a more complicated scheme if there is a benefit to it. So instead of Pavarotti we get three choir boys with three small balloons. Two of the choir boys are blowing up their balloons while the third one has his connected to the hose intake. Then they switch off in a three phase sequence so that there is always a balloon connected to the hose intake.

Phase 1: Albert inflates, Billy inflates, Charlie's balloon deflates into the intake.
Phase 2: Charlie inflates, Albert inflates, Billy's balloon deflates into the intake.
Phase 3: Billy inflates, Charlie inflates, Albert's balloon deflates into the intake.

This has several advantages:

Number one; since a balloon is always connected to the input hose, the input power is smoother. (ALL ELSE BEING EQUAL)

Number two; three choir boys and three small balloons may fit more easily into the space available.

Number three; three choir boys and three small balloons may costs less than Pavarotti and a big balloon.

Number four; with three choir boys and three small balloons you can keep the power adequately smooth with a smaller balloon on the MB. (Reduce the cost in capacitance.)

Is three phase power better? Well it might be, but it might also be cheaper while being equally good or even worse.

If you believe your home stereo sounds better when the speakers are hooked up with 4 Gauge welding cable instead of ordinary 18 Gauge zip cord, then you certainly ought to get yourself a MB with a "3-phase power solution".

If you'd prefer getting a few more watts per channel, to bragging about the size of your cable, then whether or not a board has a "3-phase power solution" is probably not going to be an important issue for you. It isn't total BS though. Power system design for motherboards is sophisticated stuff, and is an area that can make a serious difference in the profitability for a manufacturer. There is ALWAYS a trade off between power quality and cost. When a motherboard manufacturer says something along the lines of, 'Our new MB with a 3-Phase power system has the capability of powering the latest generation of processors with far better [Insert Miscellaneous Category Here] than other manufacturer's 2-Phase systems.', they are just blowing smoke. I can design a "single phase power system" that beats theirs in whatever category they choose. You may not want to pay what it costs though. It's all tradeoffs.

It sounds like Abit recently went a hair too far on the cheap side, and has had capacitors blowing up on their boards. I'm not going to knock Abit though, they may well have gotten screwed by a capacitor supplier. I'm writing this on an Abit MB that has been running 24/7 for five years with the processor overclocked 36%. (BH6 board Celeron-300A clocked at 450. Not much MHz by todays standards, but you don't often see 50% overclocking these days either.) I may well buy another Abit motherboard in the next month. However, Abit's Capacitor issues illustrate the fine line that all MB manufacturers have to walk to make a profit.

Sean "Yes, I am an engineer" Hershberger

P.S. And no, I do not work for a motherboard manufacturer.


All original content copyright James Rolfe.
All rights reserved. No reproduction allowed without written permission.
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