About VRMs & MOSFETs / Motherboard Safety with high-TDP processors

The original discussion thread for this article is located at [CLICK HERE].
As the new OCN Articles system is open and editable by anyone, please feel free to correct any mistakes possibly made in this article.

-xd_1771, original writer

A member suffered a mere 44 minutes before I wrote this article
It may be asked: what's the big deal with VRMs, mosfets and power phases...

Oh yeah, they're a pretty big deal indeed.

The majority of you are drooling on CPUs with 125W or similarly high TDP and overclocking them like you were beasts.

The majority of you also don't need expensive boards with features and like to cheap out by getting unreliable boards often with low-end cheap VRMs, i.e. a low quality 4+1 on AM3 or a low quality 6 phase on LGA1366.
You will see me often warning users about VRM setups (i.e. IT'S GOING TO BLOW UP, LOCK THOSE CORES NOW!! or STOP, get another motherboard and NOT THIS ONE)? Because it's not safe. Many of those boards really aren't even at the best value either! Usually at certain budgets (i.e. $80-100) you could get better boards with better VRMs for the price too. Anyways, I'm tired of waving my arms and screaming at people about mosfets/VRMs in every related thread I see (actually I feel this is somewhat starting to ruin my reputation on here ) so I've decided to finally complete my write up. A well-known OCN PSU guru once said...

So anyways, let's answer some questions.

Let's simplify things and start with how VRMs work:

Okay, what is a VRM system anyway?
The VRM (voltage regulator module) is the term for usually the entire area to the left of the CPU socket, containing the PWM controller, MOSFETs, chokes, and respective channels. These are responsible for converting the output voltage from the power supply (12V, 5V, 3.3V) to the lower voltages that your CPU uses (i.e. 1.2V, 1.5V, etc.). Technically where different voltages are required, a VRM system will be required. I will however be focusing on the CPU VRMs; these are located to the left of the CPU socket. As the CPU VRMs are the VRMs on the motherboard that output the most heat and have to handle the most current they are of particularly high importance.

• What is a mosfet? A MOSFET (Metal Oxide Field Effect Transistor) is a part of the voltage regulator module usually to the left of the CPU socket. The MOSFETs themselves are transistors that converts the 12V voltage into the VDIMM that the CPU uses; these are all active transistors so this is the part that gets hottest. This element is crucial because it pretty much does all the power conversion and generates the most heat, and are the most fragile in a VRM system. Usually if MOSFETs are heatsinked it is better and if they are active cooled by fan it is even better, but if there are more phases and therefore less power going through each mosfet, it's not as unsafe and unheatsinked operation may be safe to a point.
• What is a phase or channel? Basically the more phases you have, the more reliable operation because power is split between more phases; the more phases may be smaller, but nevertheless this can be much more reliable, as each component has to handle less current and outputs less heat. More phases/channels is better. Such bigger phases (i.e. 8+2) can be only found on ATX boards usually.
• Is it easy to tell how many phases there are on a motherboard? Yes. See those big black squares called chokes? (They're inductors, boxes containing coils that basically help filter and limit the current). Count them. If you see 10... usually means an 8+2. 5... usually a 4+1. Sometimes there are different combinations depending on the platform. Note that amount of chokes will not necessarily mean that you have that amount of phases (due to such things as split phasing), however a split 4+1 phase with 8+2 chokes is still capable of handling more current than a 4+1.
• The entire process is controlled by the pulse-width modulation, a frequency output that the VRMs use to stabilize/cleans up the bulk of the power going through. PWM chips on motherboards usually control the amount of (true) phases that are outputted. PWM frequency and modulation can have an effect to the amount of vDroop (voltage droop) you experience, as well as power delivery stability. High quality analog PWM systems will result in little to no vDroop. In a newer digital PWM system, PWM signal to control the VRMs is digitally modulated. This may allow for more stable voltage delivery (i.e. no vDroop). Note that vDroop is actually an Intel spec designed to enable power savings and may be enabled on purpose as opposed to having to do with the quality of the VRMs and PWM controller.
• The type of CPU connector (4/8-pin) does not have anything to do with the VRMs - you could have 8-pin + 3+1 phase or 4-pin + 8+2 phase. The 8-pin CPU power connector vs 4-pin is not important when you consider the amount of power the connector can deliver, but 8-pin connectors usually results in more voltage stability and less vDroop. vDroop can make it tougher to overclock. Just something to consider.
• VRMs also have a play in overall system power efficiency. VRMs display similar characteristics to a power supply. They also have an efficiency level; a larger VRM system (i.e. an 8+2 phase system) would be more efficient at converting the input voltage to output voltage and have less waste power & heat, similar to an 80+ rated power supply. This will also result in less amps being pulled from the power supply - and as a result, less heat from there and less chance of failures. Higher phase count can also result in the utilization of cheaper transistors, without sacrifice of power output capability and resulting still in less heat output and lower cost.

VRMs on certain platforms

• On AMD AM2+/AM3 systems: split power phase. Usually this means the majority of the phases actually bring power to the CPU, and that auxiliary phase powers the integrated memory controller/IMC. This is why VRMs are advertised in phrases such as "4+1" or "8+2" rather than simply 5-phase or 10-phase.
• On Intel LGA1156/LGA1366 boards this is similar
• On Intel LGA1156/LGA1155 boards with chipsets that support the integrated graphics, the phases are arranged as, for example: 4+1+1: 4 phases for CPU, 1 for integrated graphics, and 1 for memory controller. On LGA1156/LGA1155 boards without integrated graphics support (i.e. P55, P67) and on LGA1366, phases are arranged similarly to AMD (i.e. 4+1, 6+2, etc.)
• AMD's new socket FM1 works differently from LGA1156/LGA1155; the GPU portion of the APU shares the voltage & power phase with the CPU portion. Therefore power phase work as the usual 4+1/8+2/etc on other AMD boards (CPU/GPU + IMC), not 4+1+1 as on Intel boards.
• Older boards (i.e. before AM2+, LGA775) do not feature split power phase; the channels are not separated for certain items such as memory controller because they don't require a different voltage or more power yet, or the memory controller simply did not exist on CPU. Boards are advertised as such: 3-phase, 6-phase, etc. The VRM components were usually somewhat more separated on these older boards, this actually helps since the heat of one area doesn't spread as easily to the other. The memory controller is on the Northbridge on FSB-based platforms such as LGA775, for which power is taken from the main 24-pin connector.
• Memory (RAM) power is always taken from a separate VRM system linked to the 24-pin connector, not the CPU VRM system.

The importance of power phase count
Now, does amount of phases have everything to do with a motherboard? Usually, but this is where brand name gets taken into account. For example, The majority of 2010-released MSI AMD motherboards with 4+1 phase or similar, heatsinked or not, were far from good quality. This is due to the utilisation of transistors that may not be properly rated, and driver chips not properly rated. However, take the Biostar TA890FXE, it comes with a similar 4+2 power phase. High amperage rating per transistor; completely rock-solid. It should be noted that an 8+2 phase system may not necessarily provide any more current than a 4+1 phase if the amount of amperage available to the transistors per phase is the same; however, the 8+2 phase system would still do so with more efficiency, stability, and with less heat output. 4+1 systems or less on CPUs can be particularly risky due to the fact that each transistor must be capable of outputting more current and heat. Sometimes these will also use cheaper transistors as well. This is why you normally see motherboards with low phase count failing (i.e. catching fire, frying, overloading), often on motherboards from only certain manufacturers or certain particular motherboards.Now, mosfet quality can be hard to understand.

Phase count can still matter. Most of the culprits for VRM failures are the lower end 4+1 phase and 3+1 phase motherboards that aren't equipped to handle processors that consume lots of power and may be overclocked. Failures on motherboards with higher phase counts have been relatively infrequent - so infrequent that it can be called rare.

The situation of power phase count can be summarized in the following two sentences (in case the above was too long and complicated for you) by OCN PSU editor Phaedrus2129:

VRM system quality and design
The quality of the VRM system in question and capability of handling processors that require lots of power usually comes down to these things:

• MOSFET amperage rating denotes how many amps each MOSFET are capable of. There are two MOSFETs for each phase: high side and low side. If these MOSFETs each are rated for a not very high amperage level, these may be unsafe to use for higher TDP processors. Many MSI boards lack amperage capability and fail due to over current. Unfortunately it is not usually obvious what the MOSFET amperage rating is on the motherboard, and spec sheets will have to be searched and found. Hence, the existance of the AMD Motherboard VRM Information List to inform the user about VRM quality. A low quality board can indicate that the MOSFETs are not rated for enough amperage for higher TDP applications. Transistors usually have their model no. imprinted on them in small print. This model no. can be searched online to obtain detailed documents describing the capacity of the particular transistor, including amperage rating.
• You can see that mosfets per channel are usually in groups of 3 or 4. Usually on a good quality motherboard you will see 2 primary transistors (MOSFETs themselves) - 1 or more "high side" transistors and 1 or more "low side" transistors - and one or two slightly smaller transistors nearby called MOSFET drivers. Some motherboard manufacturers (particularly lower end ones that cannot devote as much cost into their motherboard) may choose to lower the cost on some motherboards and instead of a proper driver use a third transistor chip. This is a sacrifice of quality & reliability. While this may be fine esp. for lower CPU power applications, some boards that use a 3rd transistor driver chip use an improperly sized chip, causing problems and failures with high TDP application. It is more common that VRM failures occur with such boards. Note that the driver chips are sometimes integrated with the PWM controller, in a not so obvious fashion - so don't fret if you happen to think that they are entirely missing.
• Smaller mosfets are usually always low RDS (on). Low RDS (on) fets much more efficient and cooler. Other style MOSFETs may also be low RDS (on) but this may not be obvious.
• Although motherboards with higher phase count can use lower quality transistors, this does not mean it will supply less current than a lower phase count motherboard with higher quality transistors. The higher phase count motherboard would have the additional advantage of higher power delivery efficiency, cooler running (resulting in lower chance of common failure by overheat)
• Driver MOSFETs (also known as DrMOS) integrate the MOSFETs and the driver into one package. Note that while this can result in more efficiency, driver MOSFETs can be more fragile and failure prone at high voltage and current. This is rather noticeable on the Intel side of things, where most newer driver MOSFET boards are failing due to over current, usually (only) during extreme overclocking scenarios. The combination of low phase count and driver MOSFETs on the infamous MSI 790FX-GD70 (and succeeding 890FX-GD70) resulted in a board that was particularly known for VRM failures in high amperage scenarios (i.e. Phenom II x6). The MSI 890FXA-GD65 and new 8+2 MSI motherboards have doubled the amount of phases - and driver MOSFETs - resulting in higher possible amperage capability. Although these driver MOSFET motherboards with larger phase count are still more prone to failures (which have happened on these boards), the problem is not nearly as rampant as with more phase count, each of the driver MOSFET can supply less amperage and run under less heat and stress.

A proper MOSFET design will have two primary MOSFET chips (high side and low side) and one or more driver chips. MOSFETs are rated for a certain amperage; this may not be obvious and will require searching for spec sheets on the internet for more info, hence the existance of the AMD Motherboard VRM Information List to inform the user about VRM quality. A low quality board can indicate that the MOSFETs are not rated for enough amperage for higher TDP applications.

What VRM cooling will do for you
VRM cooling is an important part of keeping VRM temps down. VRM cooling is usually placed on the MOSFETs, active transistors that are the most fragile and the hottest. Often the VRMs get little to no air so as much heat radiation as possible would be best. What I recommend you do in terms of cooling the VRMs and running a high TDP processor:

• Add any sort of VRM heatsink such as MOS-C1 if there isn't already, especially on 4+1 boards even with quality
• Add active cooling. A small fan, or Spot Cool, will do. While most VRMs will run safe with VRMs and no active fan cooling, huge temperature drops have been shown from even really weak 40MM fans that don't push much air.
• Improve on case airflow. i.e. add that top fan in the slot above the VRMs (heat naturally dissipates upward).

OCN member mdocod has found that as of 3 March 2011, at least 71% of the VRM cooling failure incidents in the compiled list of horror stories have happened on a cooling that deviates from stock cooling. This value may be higher due to the amount of situations where cooling was not described.

"Stock" CPU cooling is designed to blow down onto the motherboard components, including VRMs. This includes: tower cooling, any sort of water cooling. Remember, TDP rating on all boards is done with processors at stock and with stock cooling. That means your 4+1 phase or even 3+1 phase (on AMD platform) may actually be fine for a more power consuming (i.e. 125W TDP) processor with stock cooling & at stock speed, but deviate any one of these and you're on your own.

Motherboard TDP ratings and how they relate to VRM quality
A lot of people claim that their boards are rated TDP at 125W-140W and it's still safe to run that processor on that board. Not that you should take these ratings with a grain of salt, but you should be reminded that all motherboards are ratified in TDP capability, with processors at stock speed and with the stock cooler installed. (Note that although TDP has more to do with processor heat output and choice of stock cooler, it is closely related to the processor's actual power consumption). At stock speed you are within that TDP limit and with the stock cooler, air blows past the heatsink fins and onto the board, so some air gets to the VRM area and other motherboard components for cooling. When you overclock, you're then exceeding these limits, which may bring additional heat and instability into the VRMs (can be fixable with MOSFET heatsinks and fan). Overclocking is usually associated with aftermarket heatsinks, many tower heatsinks that blow over the motherboard; this removal of VRM cooling may significantly increase chances of catastrophe. At least 70% of all VRM failure incidents happen with aftermarket CPU cooling installed. Motherboards with lower phase count and lower rated transistors usually have VRM systems that run hotter and are more prone to failure. Heat causes a lot of VRM problems including unstable power delivery and even fire hazard. Proper MOSFET/VRM cooling may help, and some boards allow you to monitor VRM temps (i.e. TMPIN2 on HWMonitor on some Gigabyte boards - for your board it may depend, TMPIN2 may exist or may not at all and it may not even be VRMs). Though different VRM systems may be rated for temperature differently, ideally the temperature should be the same as the CPU load (i.e. my VRMs load at around 60, with my CPU tagging along at slightly lower than that). Typically, proper VRM cooling installed will allow for higher TDP capability as the VRMs can run under less heat and stress - as a result the TDP is rated higher than usual for stock speed operation.

My CPU speed is throttling even if it is stone cold!
Over Current Protection (OCP) is something I have recently been examining. Protection features exist against VRM overheating/overloading depending on motherboard model and brand. I believe it is a crucial feature on motherboards today, because this is the function that will protect your VRMs from a catastrophic failure. This is why I have never seen ASUS boards fail even if people take a lowly 3+1 ASUS boards and try to overclock a Phenom II x6 on it; ASUS boards feature this technology, it is a part of the PWM controller design. OCP can work in various ways; one of the ways it works is it downclocks the CPU speed & voltage - via cool'n'quiet or it's own function - if the VRM temperatures are detected as too high (similar to if CPU temps are too high), until they can recuperate and lower in temperature. As a result, it can reduce performance during a full load scenario. It is also how ASUS gets away with rating a few select 3+1 phase AMD motherboards at 125W, though at times the OCP may kick in too often at load even at stock speed/stock cooler and the rating would've been slightly improper for the board (there is no 3+1 phase board ready for 125W processors). Another common way is a full board shutdown; if MOSFETs are overloaded suddenly to the point where immediate shutdown is needed for protection (i.e. beginning an OCCT run on a 3+1 power phase on a Phenom II x6 OC'ed and at 1.5V), then OCP will kick in and the board will shut down to protect itself. ASRock boards and some Gigabyte boards are known for this. Some boards will do this past a certain point. Others don't. OCN members and I have found that most recent MSI AMD boards feature NO protection of any sort against VRM failure/over current/over temperature, and this is likely why a majority of the catastrophic failures in the horror stories list are MSI boards. At the moment I and others have been trying to find out which brands/specific motherboards do use over current protection, and we are listing them down for future reference. Once that is done, take it at heart to purchase a board with OCP for your own safety and for the best confidence in overclocking.

This next portion would have to do on how badly the importance of VRM quality is underestimated....

^^^^ And that would be all the VRM failures/situations I have ever found compiled onto one extremely long list. There's so many on here that it's not even worth mentioning elsewhere. When I say "don't make me bring out the horror stories"... I'm serious, don't make me bring out the horror stories. And, yeah, never underestimate the importance of a quality VRM setup.

(Please send a private message to OCN member xd_1771 if you wish to have an entry added to this chart. Note that a form usable by you to add your own entries is under construction).

In conclusion... as a good basis I usually suggest or buy boards with reliable VRMs and cooling, according to the CPU TDP. For 125W, as a rule of thumb I usually stick to an 8+2 or otherwise smaller but quality power phase. Not that 4+1s are bad, quality ones with proper cooling can actually handle overclocks on high TDP processor; you just have to be a bit picky and choose the right board. Some tips for doing that are above

Board-specific VRM info:

A list of all AMD motherboards with detailed VRM information including quality/amount of phases can be found here.

So what exactly is good and bad again?
Well, assuming you read the whole article, if you are planning to buy a motherboard, this is what you do:

AMD Platforms on high TDP (~125W) processor (includes unlocked CPUs):
Remember, you can refer to the AMD Motherboard VRM info article/table for info about specific motherboards (see link above)

• Look for a minimum quality 4+1 phase on the board for use with high TDP processor. Higher is better though.
• Be SURE it is of quality; if so,
  • Preferably low RDS (on) transistors
  • A proper transistor design and proper transistor amperage rating
  • On a brand that is not known for VRM failures.
  • If you are overclocking with a high TDP processor and a 4+1, consider MOSFET/VRM cooling a MUST. Some boards may already have this. Fewer phases will overheat much easier and be more prone to failure.
• If you have enough budget to get a board with a better, larger VRM system (i.e. 8+2 phasing or similar) and/or room for larger board size (mATX boards are typically fitted with inferior VRM designs due to limited space), there is not much need to worry.
  • Cooling is no longer as big an issue because the larger amount of (smaller) transistors can run cooler over a larger area as they have no need to handle as much current.

Intel platforms on high TDP processor:
The rules are similar, however do pay attention to the overall TDP of the majority of Intel processors. Some platforms set a 95W max, this consumes less power and may require less phases for good functionality, even overclocked.

A few last notes:

• Some of you may get word about 8+2 phase basically being a 4+1 phase and not being true 8+2 phase. This is actually true, a lot of what I usually call 8+2 anyway just for simplicity, is actually something called 4+1 split; there are 4+1 channels, but the components (i.e. chokes, mosfets) are split as if they were an 8+2 phase; this is quite close enough to the quality of a true 8+2 phase on a reliable PWM controller. My own motherboard (the Gigabyte MA790XT-UD4P) would be a good example of this. Once again I usually call those 8+2 phase anyway just for simplicity.
• My list of horror stories grows constantly... feel free to check back for updates every couple of weeks or months or so!
• Concerning Driver MOSFETs where the transistors & mosfet drivers are merged into 1 big chip... do they mean quality? Not necessarily. Take for example: MSI's 790FX-GD70 and 890FXA-GD70. They both have these new Driver MOSFETS (DrMOS) that are supposed to run much cooler and better, and yet they still are known to blow up at high voltages & high TDP processors just as with other MSI AMD motherboards released in 2010. This is probably a problem somewhere else then, i.e. the chokes, or PWM controller.
• I've been planning to do a write-up like this for while, but I probably made a lot of mistakes writing this... be sure to tell me if so

Other important VRM system-related resources

• A clarification of phases; also, RE: exploding GTX590s - OCN PSU editor Phaedrus2129's take at explaining VRMs and why VRM failures have often occured on the nVidia GTX 590.
• AMD motherboard VRM information list - Information lits regarding VRM phase count, quality, TDP rating of all AMD motherboards.

What to do if you suspect your VRMs have failed

1. Unplug everything/cut power to the PC
2. Check for visible damage (blown caps, missing parts from mobo, burn marks) [this might not always be the case]
3. Use your sense of smell (if they blew it'd be pretty obvious to the nose, but it might smell really bad)
4. Put out the fire! (If there's any)
5. Run standard troubleshooting procedures to make sure it's not anything else (i.e. check the power supply)
6. Try testing the motherboard with the 24-pin plugged in but without the 4-pin/8-pin CPU power plug. This is the ultimate dealbreaker; if the motherboard only boots when CPU power plug is unplugged (though it obviously won't POST), you sir have a VRM failure on your hands.
7. Report it here! The more VRM horror stories are in the posted horror stories list, the more aware this can make people about this overlooked issue.

Remember, not all VRM failures are visible and involve fire & explosions! Boards will sometimes quietly go with a shutdown and not boot again. Sometimes VRM failures can take out other parts, as with PSUs, and sometimes not.