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Home » Motherboard
Everything You Need to Know About The Motherboard Voltage Regulator Circuit
Author: Gabriel Torres
Type: Tutorials Last Updated: February 10, 2010
Page: 4 of 6
Phases (Channels)

The voltage regulator may have several power circuits working in parallel to provide the same output voltage – say the CPU core voltage. They, however, are not working at the same time: they are working out-of-phase and hence the name “phase” to describe each circuit. We will explain in details in the next page how this works, so don’t get scared. We want to present an introduction to this subject, since manufacturers and enthusiasts like to discuss the number of “phases” a motherboard has a lot.

Let’s take the CPU voltage regulator circuit. If this circuit has two phases (or channels), each phase will be operating 50% of the time in order to generate the CPU voltage. If this same circuit is constructed with three phases, each phase will be working 33.3% of the time. With four phases, each phase will be working 25% of the time. With six phases each phase will be working 16.6% of the time. And so on.

There are several advantages in having a voltage regulator circuit with more phases. The most obvious is that the transistors will be working less loaded, which provides a higher life-span to these components and a lower operating temperature. Another advantage is that the more phases you have usually the output voltage is more stable and also the noise level is lower.

Adding more phases require adding more components, which increase the cost of the motherboard: cheaper motherboard will have fewer phases, while more expensive ones will have more phases.

Also it is very important to clarify that when a manufacturer says that a motherboard has six power phases, it is referring only to the CPU main voltage (Vcore). On next page we will explain in more details what happens when the CPU requires more than one voltage.

Each voltage phase or channel uses one choke, two or three transistors (or a single integrated circuit replacing these transistors), one or more electrolytic capacitors and one MOSFET driver integrated circuit – this last component can be replaced by a transistor, as which is the case with low-end motherboards. As you can see, the exact number of components will vary. The only component that is present with always the same count is the choke, so the best way for you to know how many phases a given voltage regulator circuit has is by counting the number of chokes (pay attention because there are exceptions; we will explain them next). For example, the motherboard in Figure 11 (the same board shown before on Figures 1 and 2) has three phases.

Motherboard Phases
click to enlarge
Figure 11: Phases.

But there is one caveat. On some motherboards the phase that controls the memory or the chipset voltage is located close to the other phases, making you to have a wrong phase count if you simply count the number of chokes present near the CPU socket. We show this case in Figure 12: even though the portrayed motherboard has four chokes, it is a three-phase motherboard, as only three of the phases are used to generate the CPU main voltage (Vcore); on this motherboard the fourth phase is used to generate the memory voltage. We will teach how to get the exact phase count in just one second.

Motherboard Phase
click to enlarge
Figure 12: Motherboard with three phases, not four as you could assume.

It is wrong to assume that only chokes near the rear end of the motherboard should be counted, ignoring chokes located on the side of the board: in Figure 11 you can see a motherboard with a choke located on the side that belongs to the CPU voltage regulator circuit…

Since all chokes that are producing the same output voltage have their outputs connected together, only chokes that have their outputs connected together should be counted. This can be done by following each choke output on the solder side from the motherboard. In Figure 13 we show the solder side from the motherboard shown in Figure 12. As you can see, only three chokes are connected together, the output from the fourth choke is going down to the memory sockets (we know this because this was a socket LGA775 motherboard, where the CPU only requires a single voltage; detailed info will be given in the next page).

Voltage Regulator Phases
click to enlarge
Figure 13: Correct way of counting chokes.

On some motherboards you may not clearly see the connection between phases like we are showing in Figure 13. In this case you have to get a multimeter and check which chokes are connected together. You can either but your multimeter on its continuity scale (if it has one – usually beeping when the probes are "shorted", indicating that there is connection) or resistance scale (which will show zero ohm when there is a connection). On Figures 14 and 15 we show another motherboard with four chokes where the connections of the chokes isn't clear like on the motherboard from Figure 13. With a multimeter we discovered that three of the chokes were connected together, thus this was a "three-phase" motherboard. The fourth choke was feeding something else (the CPU integrated memory controller, as we will explain in the next page).

Detecting a Phase
click to enlarge
Figure 14: These two chokes are connected together.

Detecting a Phase
click to enlarge
Figure 15: These two chokes aren't connected together.

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