VRM design - why more phases (motherboard, videocard)? - Page 1
Forum section: electronics / projects

author: nForce
author_rank: Frequent Contributor
timestamp: December 06, 2023, 07:39:53 pm
content: I don't quite understand why do we need more phases for Voltage Regulator Module? I only understand that it is a buck converter and decreases from 12 V supply to 1 V. This voltage level is OK for the CPU or GPU.Thanks for the clarification.

author: moffy
author_rank: Super Contributor
timestamp: December 06, 2023, 08:03:54 pm
content: The more phases shares the load current across multiple devices, it is a way of paralleling, also with such a low duty cycle multiple phases which are phase offset from one another will help reduce ripple.

author: Konkedout
author_rank: Frequent Contributor
timestamp: December 07, 2023, 05:07:17 am
content: More phases give you more output DC current with less peak-peak ripple current. Also the inductors work effectively in parallel to improve the ability to maintain constant output voltage as the load current varies rapidly.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 07, 2023, 06:54:32 am
content: Draw the input current waveform when bucking from, say, 12V 10A to 1V 120A. Then draw the input current waveform when bucking from 12V 1A to 1V 12A and copy-pasta the same spikes 10 times at different positions. You will instantly understand the difference.

author: Jeroen3
author_rank: Super Contributor
timestamp: December 07, 2023, 07:01:27 am
content: Processors requirea lotof current.Maybe this helps: Intel Raptor Lake datasheethttps://www.intel.com/content/www/us/en/content-details/743844/13th-generation-intel-core-and-intel-core-14th-generation-processors-datasheet-volume-1-of-2.htmlEg: IccMAX for an S-Processor Line (150W) 8P+16E is 307A max.

author: coppercone2
author_rank: Super Contributor
timestamp: December 07, 2023, 07:53:19 am
content: the components that can do this easy dont existi think if we could get our hands on some AB condensers then the polyphase converter might be seen as a rupe goldberg topology."It's a bead condenser, model AB 619. It has a breakdown voltage of 33,000 volts. A diamond drill won't touch it. It comes from a mysterious vendor called Electronics Service, Unit No. 16. There's no charge and no return address. The catalog pages are made of some kind of metal."

author: Kleinstein
author_rank: Super Contributor
timestamp: December 07, 2023, 08:16:33 am
content: The multiphase configuration reduces ripple, as the ripple from the phases partially cancels out. This helps to get away with less capacitors.The 2nd point is that at the same frequency the possible reaction speed gets multiplied by the number of phases. Keeping the switching frequency low helps getting better efficiency and less EMI.The normal PCBs already now have a hard time with that much currrent in a small area and sharing the current over several phases helps a little, though there is still the ripple current to overlap.

author: Berni
author_rank: Super Contributor
timestamp: December 07, 2023, 08:31:13 am
content: Similar reason why we use 3 phase power all over the world. The overlapping phases provide a smoother more continuous flow of power.This way much less capacitance is needed to smooth it back into clean DC voltage. Also since modern CPUs and GPUs require multiple 100s of amps of power, using multiphase makes the design easier when you can spread the load over multiple smaller inductors and switches that only need to provide multiple 10s of amps now. Even just running 100s of amps trough a PCB is a serious design challenge, let alone having it pass trough a single component. The P=R*I^2 really becomes problematic once that amps squared shoots off to the moon

author: ArdWar
author_rank: Frequent Contributor
timestamp: December 07, 2023, 08:53:26 am
content: It's definitely started for performance reason, but at certain point it surely shifting into marketing BS. No oneneed16 phase VRM, and most high phase count VRM aren't even "real" phases. 12 or 16 phases for example are almost certainly actually 6 or 8 phase with each phase driving paralleled half bridge