Voltage Regulator Module (VRM) is an electronic circuit that regulates and down steps voltage from its input (e.g., system power rail) to its output (e.g., integrated circuits) while stepping up current. In the context of a typical computer, the VRM converts the 12/5/3.3 V DC power rail that comes from the power supply unit into the much lower operating voltage of the integrated circuit (e.g. 0.8 V, 1 V, 1.2 V). VRMs are typically implemented as a switching regulator such as a buck converter due to their efficiency.

Overview

Single-phase

Generally, a VRM circuit is usually implemented as a buck converter, but this is not strictly the only way to design it. Shown is a basic schematic of a VRM circuit. On the left side is the typical 12 V which comes from the power supply unit. There are two MOSFETs just before point A, a low-side and a high-side, which serve as actual switches. To the left of point B is the choke (or a filtering inductor).

The goal of the circuit is to take the power supply voltage which is 12 V before point A and convert it to the much lower operating voltage of the CPU or GPU at point B which is something like 1.2 V.

Operation

When the high-side switch is closed, the voltage at point A becomes 12 V but the voltage at the other side of the inductor doesn't change instantaneously, instead, the voltage builds over time as the inductor continue to resists change in current. The below graph depicts the voltage that would be fed to the CPU/GPU at point B if the high-side switch was to remain closed for a sufficient amount of time:

Multi-phase

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