Voltage regulator module
A voltage regulator module or VRM, sometimes called PPM (processor power module), is a buck converter that provides a microprocessor the appropriate supply voltage, converting +5 V or +12 V to a much lower voltage required by the CPU, allowing processors with different supply voltage to be mounted on the same motherboard.
Some voltage regulator modules are soldered onto the motherboard, while others are installed in an open slot. Some processors, such as Intel's Haswell, feature voltage regulation components on the same package as the CPU, instead of having a VRM as part of the motherboard. Most modern CPUs require less than 1.5 V, as CPU designers tend to use smaller CPU core voltages; lower voltages help reduce CPU power dissipation, often referred to as thermal design power (TDP).
Some voltage regulators provide a fixed supply voltage to the processor, but most of them sense the required supply voltage from the processor, essentially acting as a continuously-variable adjustable regulator. In particular, VRMs that are soldered to the motherboard are supposed to do the sensing, according to the Intel specification.
The correct supply voltage is communicated by the microprocessor to the VRM at startup via a number of bits called VID (voltage identification). In particular, the VRM initially provides a standard supply voltage to the VID logic, which is the part of the processor whose only aim is to then send the VID to the VRM. When the VRM has received the VID identifying the required supply voltage, it starts acting as a voltage regulator, providing the required constant voltage supply to the processor.
Instead of having a power supply unit generate some fixed voltage, the CPU uses a small set of digital signals, the VID lines, to instruct an on-board power converter of the desired voltage level. The switch-mode buck converter then adjusts its output accordingly. The flexibility so obtained makes it possible to use the same power supply unit for CPUs with somewhat different nominal supply voltages and to reduce power consumption during idle periods by lowering the supply voltage.
For example, a unit with 5-bit VID would output one of at most 32 (25) distinct output voltages. These voltages are usually (but not always) evenly spaced within a given range. Some of the code words may be reserved for special functions such as shutting down the unit, hence a 5-bit VID unit may have fewer than 32 output voltage levels. How the numerical codes map to supply voltages is typically specified in tables provided by component manufacturers. As of 2008 VID comes in 5-, 6- and 8-bit varieties and is mostly applied to power modules outputting between 0.5 V and 3.5 V.
- "Intel's Haswell Takes A Major Step Forward, Integrates Voltage Regulator". hothardware.com. 2013-05-13. Retrieved 2013-11-14.
- "Graphics Cards Voltage Regulator Modules (VRM) Explained". geeks3d.com. 2010. Retrieved 2013-11-28.
- Intel document "Voltage Regulator-Down (VRD)" 11.0 http://www.intel.com/assets/pdf/designguide/313214.pdf dated November 2006.