The MOSFET question

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RancidWAnnaRIot

EspantaPajaros
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Feb 19, 2004
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hello,

I constantly hear you guys talk about MOSFETs regulating voltage for the CPU and other things?

I just want to make sure.. do you guys really know what MOSFETs are?? because to regulate voltage, you use a voltage regulator.. which is made up of a few MOSFETs, and a diode or two and an Amplifier...

so my question.. are these MOSFETs you guys talk about, really MOSFETs? or do you guys just don't know what you're talking about??

FYI, MOSFETs make up about 90% of all computer hardware

i'm not trying to like take a jab at anyone.. it's just.. it seems to me like people are misinformed... or maybe i'm misinformed???

maybe people are getting confused because a voltage regulator is a 3 terminal device (typically) , and MOSFETs are also 3 terminal devices..
 
In very, very general terms -

You are right. A MOSFET is basically a transistor, or when operated at saturation, a switch. However, when combined with a feedback based voltage controller, and an LC output circuit to filter switching transients and smooth the resulting DC voltage you have.....all the basics of a simple switching voltage regulator. This is how your PC works....:cool:

Regards - B.B.S.
 
That’s a confrontational message but I’ll answer it anyways.

What you describe, a MOSFET and amplifier and some diodes, is a simple method of creating a linear regulator. This is what you would typically find in a LM317 or other type of 3 terminal regulators. The problem with this type of regulator is that it acts effectively as a resistor in series with the load and can create quite a lot of heat. These types of regulators are not used to power processors, as they would need to dissipate more heat then the processor itself.

The MOSFETs that regulate the voltage for the CPU are much different then the millions of other FETs that make up a computer. These FETs typically can handle currents in the range of 20Amps each, a current that would burn out lesser FETs. As BlindedByScience has said these MOSFETs are not used as linear regulators but are used as components in a switching regulator.

If you are interested in learning more about switch mode power supplies check out Maxim-IC’s site. They manufacture power supply controller chips and have a large amount of useful information.

http://www.maxim-ic.com

Also the following link points to the information on the switch-mode controller IC I used in my last project. The datasheet describes, somewhat technically, how the converters work.

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4076/ln/
 
The Brain said:
That’s a confrontational message but I’ll answer it anyways.

What you describe, a MOSFET and amplifier and some diodes, is a simple method of creating a linear regulator. This is what you would typically find in a LM317 or other type of 3 terminal regulators. The problem with this type of regulator is that it acts effectively as a resistor in series with the load and can create quite a lot of heat. These types of regulators are not used to power processors, as they would need to dissipate more heat then the processor itself.

The MOSFETs that regulate the voltage for the CPU are much different then the millions of other FETs that make up a computer. These FETs typically can handle currents in the range of 20Amps each, a current that would burn out lesser FETs. As BlindedByScience has said these MOSFETs are not used as linear regulators but are used as components in a switching regulator.

If you are interested in learning more about switch mode power supplies check out Maxim-IC’s site. They manufacture power supply controller chips and have a large amount of useful information.

http://www.maxim-ic.com

Also the following link points to the information on the switch-mode controller IC I used in my last project. The datasheet describes, somewhat technically, how the converters work.

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4076/ln/
Click to expand...


Sounds like a power MOSFET to me.. but okay..
 
RancidWAnnaRIot said:
FYI, MOSFETs make up about 90% of all computer hardware
Click to expand...
You may be technically accurate, but it's more usual to refer to the low-power gates making up your computer logic hardware as CMOS (complementary metal-oxide-semiconductor) technology, and reserve the MOSFET label for the discrete transistors. That way, we all know what we mean.
 
There seems to be two seperate issues here. First I'll address the power mosfet issue.

RancidWAnnaRIot said:
Sounds like a power MOSFET to me.. but okay..
Click to expand...

Yes it is a power MOSFET, but why argue symantics. Technically a mosfet is a metal-oxide-semiconductor field-effect transistor. This means that the both the power transistors and the tiny transistors within a CPU can be called MOSFETs.

The second issue involves a possible confusion between a voltage regulator and a MOSFET. I gathered this issue from the thread above and another of your postings, quoted below.

RancidWAnnaRIot said:
that just sounds like a voltage regulator to me lol.. Voltage regulators are made using MOSFETs (and diode/zener diodes, and op amps).. and all modern CPUs are made with MOSFETs... i would assume the MOSFETS in the regulators are POWER MOSFETs.. since they get hot i'm sure thye handle a load of current.. hence.. Power MOSFET

I've notice peopel on the [H]ard tend to think voltage regulators are MOSFEts.. they are not... they are make with MOSFETS, op amps, and diodes.... MOSFETs are in practically 90% of all electronic devices.. including CPUs.. memory.. and much more..
Click to expand...

The three terminal devices used to regulate power on a PC motherboard are power MOSFETs, not linear voltage regulators. The MOSFETs might be able to handle more current then those in a CPU but they are the same type of devices. One could even design a simple processor using only discrete power MOSFETs. It would be huge, slow, and power hungry, but it would work.

Basically what I am trying to say is that "peopel on the [H]ard" believe that the three terminal devices on motherboards are MOSFETs, not voltage regulators, because that is what they are.

Sorry to break it to you.
 
Tyically, when folks around here say "MOSFET" they are referring to these little bastards;

mosfet2.jpg


Yeah, I realise that may not be the correct terminology, but it's what's commonly understood.
 
A FET is a kind of transistor, characterized by transconductance.
A MOSFET is a kind of FET, as apposed to JFETs and other oddball types.
A power MOSFET is a kind of MOSFET designed for high-current switching... as opposed to lateral mosfets which are used for linear amplification, planar MOSFETs that are used in radio transmitters, etc...
You can then branch power MOSFETs into trench power MOSFET and vertical power MOSFET, and then break these down further, but it's a waste of time.

Doesn't matter what you call the black thingys on your computer motherboard near your CPU... call them transistors, FETs, MOSFETs, "black thingys" and you'll be correct on every occasion.

And your motherboard's core voltage regulator can be called exactly that, a VRM, a regulator, a switching regulator, a "multiphase synchronous buck converter"... etc
 
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