For the last few years motherboard manufacturers have been announcing boards with ever-increasing numbers of phases. We wanted to go over what these stats mean. First of all, a reminder of their role: a PC power supply supplies a direct current (DC) of 12 volts to the motherboard by means of the 24-pin connector and an additional connector often called a P4/P8.
The problem is that our processors don’t run at 12 volts. The voltage you can observe with a tool such as CPU-Z is lower and, moreover, tends to vary according to processor load!
By default, CPU-Z shows the voltage read using a sensor. By adding the line Sensor=0 to the file cpuz.ini, you can also see what's called the VID, namely the voltage requested.
A voltage regulation circuit is therefore used to make the conversion. This circuit uses a PWM controller. As we saw in our report on PWM fans
, the concept behind the PWM controller is to send a discrete periodic signal, an output voltage that will determine whether or not the circuit behind it is switched on or not.
When used with a fan, the PWM controller serves to regulate the rotation speed of the blades by controlling the period during which the fan is supplied with power. The PWM signal serves as a sort of programmable periodic switch.
On a motherboard, a PWM controller works in a similar way, except that here it controls several channels, turning several circuits on and off simultaneously in an intelligent way. These circuits are called…
Without going into too much detail, a phase is a voltage regulation system (12V in, different voltage out) made up of a controller (1), transistors (2), a choke coil (3) and capacitors (4). Above and beyond the concept, which is standard electronics, it's the components themselves that have evolved.
For example, here’s a system on a slightly older motherboard (socket 1156 era). The photo highlights several points which lie behind some of the marketing communication from motherboard manufacturers.
The most commonplace concerns the capacitors. For some time now, the cheaper traditional electrolytic capacitors have been replaced with a new gen capacitor, the so-called 'solids'. The main advantage of solids is that they last longer at higher temperatures. Manufacturers talk about ‘solid caps’ in their marketing communication. Some manufacturers also tell you where they've been made, with Gigabyte for example telling us that its capacitors are made in Japan. You may remember that a few years ago some manufacturers had problems with lower quality capacitors that were subject to leakage.
Another difference is that the type of transistor used has changed. On the older designs, basic field-effect transistors (MOSFETs) were used. Manufacturers are now going for the better quality ‘Low Rds (on)’ MOSFETs. Rds(on) literally indicates resistance (R, the loss) between the drain and the source (ds) when the transistor allows the current to flow (on). Having a lower resistance allows you to apply a lower voltage. Note that on some very high-end mobos, the controller (which is the same in both our photos) may also include both transistors on the same package. Then there's a single chip in place of the controller and the two transistors for each phase. This simplifies design and energy efficiency is generally higher (as is the price!). This doesn’t however concern the motherboards in this review.
Example of a single package design from Asus
The last notable difference comes with the choke coil and the introduction of models with ferrite cores that can be recognized by the fact that they are closed and the copper coil is no longer visible. Manufacturers stress that these closed chokes reduce electromagnetic interference.