When it comes to motherboards, everyone wants something different for their desktop. Some people like to have multiple USB port options for connectivity, while some prefer multiple graphics cards for extensive gaming.
But there is one important aspect of motherboard design that people often ignore: Voltage Regulator Module (VRM). It is responsible for powering CPU and GPU.
In this overview article, we have discussed why VRM is the most crucial component, how it works, and why people should not overlook it when choosing a new motherboard.
What Is A VRM?
A VRM (short for Voltage Regulator Module) is a mini power supply connected to a microprocessor. Just like the main power supply (SMPS or switched-mode power supply) takes 240 or 120 volts from the wall socket and steps it down to DC 12 volts, the motherboard VRM does this second time to provide appropriate voltage to CPU.
VRM, also called the processor power module, is a DC-to-DC power converter that steps down the voltage, converting +12 or +5 volts to a much lower voltage required by the microprocessor.
Most VRMs provide load between 0.5 and 3.5 volts, enabling microprocessors with different supply voltage to be integrated on the same motherboard.
Modern VRMs sense the [varying] required voltage from a processor and adjust the power supply accordingly. They are soldered onto the motherboard to do the ‘sensing.’ Some GPUs also utilize VRMs due to their high-voltage requirements. Such VRMs get really hot while doing their task, so they require a heat sink to dissipate excess heat.
How Does It Work?
The VRM is usually implemented as a switching regulator due to its efficiency. Although it is just a buck converter that precisely steps down voltages to appropriate levels, its design is quite complex than a simple circuit.
The VRM is made of three components:
- MOSFET: A semiconductor device that is widely used for switching and amplifying electronic signals.
- Choke (inductor): A passive component that stores energy in a magnetic field when electric current flows through it.
- Capacitor: Another passive component that stores electrical energy in an electric field.
Single-phase VRM circuit
A VRM circuit consists of two MOSFETS (a high-side and a low-side) that serve as actual switches. When the high-side MOSFET is closed, the inductor builds magnetic fields (charges up). If the high-side MOSFET remains closed for a sufficient time, the inductor accumulates the full charge, reaching 12 volts (same as the power supply).
However, the actual purpose of the inductor in a VRM circuit is to keep the voltage from instantly reaching 12 volts. The rate of change of the voltage depends on the inductor’s inductance. A large inductor, for example, with a high inductance will change the voltage at a relatively slower rate.
When the high-side MOSFET is opened, the magnetic field of the inductor begins to collapse, producing current, which is fed to the CPU. At the same time, a sudden voltage spike is generated across the inductive load. To eliminate this spike, a flyback diode is connected across the inductor.
When the high-side MOSFET is opened, the low side switch is closed. This configuration allows the current to flow through the low side MOSFET instead of the diode, enhancing the circuit’s efficiency.
The aim of the circuit is to deliver the appropriate voltage required by the CPU. Since most modern microprocessors consume 1.2 volts, the circuit cuts off the choke charging when the voltage at the inductor reaches 1.2 volts. As soon as this happens, the voltage starts dropping. After a certain voltage drop, the circuit again starts charging up the indicator.
This cycle is repeated again and again via a method called pulse-width modulation. And that’s how the circuit maintains and delivers the appropriate operating voltage.
Usually, we do not have only two MOSFETs, one inductor, and one capacitor for the whole CPU system. Most VRMs utilize several MOSFETs, several inductors, and several capacitors (connected in parallel) to power a microprocessor.
Advantage of Multi-phase VRMs
In a multi-phase VRM, each phase handles a portion of the total current that the CPU/GPU requires. For example, when a CPU needs 50 amperes, the two-phase VRM splits the current between two phases. So 25 amperes is transmitted through the first phase, and the other 25 amperes is transmitted through the second phase.
This means if you have two power phases, each phase works 50% of the time. And if you add a third phase, each phase will only work 33% of the time, and so on.
VRM four-phase diagram
The more power phases you have, the more reliable the VRM is. In particular, the more power phases you add, the cooler each phase runs, and the more power VRM can put out, providing more stable voltages to the microprocessor.
Cooler operation increases the VRM’s lifespan and decreases the overheating risk. Better stability of power for the processor can also reduce the required voltage for overclocking stability to some extent.
It is important to understand that the quality of VRM cannot be improved by just adding more power phases. The actual components and their circuit integration play a major role in determining how much power the VRM can handle and for how long it can output stable voltage.
A low-quality VRM can degrade a processor’s performance and limits its ability to operate under load. It can also result in unexpected shutdowns, especially when overclocking.
VRM components on the motherboard
Today’s VRMs consist of 6, 8, 12, and even 16 phases to provide optimal performance at reasonable prices. A few manufactures sold VRMs as something like “6+2” or “8+3.” The value before the plus sign shows the number of phases dedicated to power a CPU, and the value after the plus sign shows phases dedicated to other components such as GPU or RAM.
VRMs are also placed next to the RAM slots on the motherboard. But since RAM consumes much less power than the processor and only a few people do RAM overclocking, it is often ignored.
How Does CPU/GPU Use VRM?
Most VRMs do not produce a fixed voltage. Instead, they get digital signals from the microprocessor, which instruct them about required (varying) voltage levels.
At startup, VRM provides a predefined voltage to the microprocessor. The processor then communicates to the VRM through a number of bits known as Voltage Identification Definition (VID).
Once VRM receives the VID, it decodes the needed supply voltage and starts operating as a voltage regulator, continuously providing the required power to the microprocessor. It also minimizes power consumption during ideal intervals by reducing the supply voltage.
For instance, a unit with 6-bit VID outputs one of 64 (26) distinct output voltages. These voltages are generally spaced within a specific range. A few numerical keys are reserved for certain operations, such as restarting the unit. Component manufactures provide specific tables that specify how these keys map to supply voltages.
How To Look For Good VRM?
Some motherboard manufacturers increase the number of components used in each power phase, without actually increasing the power phase count. MSI’s B450M Mortar and ASUS’ Z390 Maximus XI Hero are examples of such design.
Some manufacturers claim a higher phase count by just adding a few chokes and transistors. Although it gives the appearance of more phases, it doesn’t actually add any separate phase. ASUS’ TUF Z370-Pro Gaming, Biostar’s B450MHC, and Gigabyte’s B450 Aorus M are examples of such design.
These tactics are common in the market. Thus it is very difficult to determine the power phase count by just looking at the number of capacitors and inductors on the motherboard.
The only correct way to determine the number of power phases is to analyze the actual component by yourself or seek out an authoritative source that has done this sort of analysis on the motherboard you are considering.
Don’t Stress Over VRMs
For typical users, who mostly use their computer for browsing and watching movies, it is not worth stressing out over the VRM. It is best to focus on the features and design of a motherboard.
However, users who are running a processor with 16+ cores or trying to break overclocking records will definitely get the benefit of using high-end VRMs with over eight power phases.