Newb question: WHY do vmods work?

[exscape]

Soldering a VR between a point and ground seems to be one of the most common voltmods around (for most chips, that is).
What I don't understand is why lower resistance -> more voltage. How does this work? :confused:

BTW, I just did my first voltmod, on my NF2 board. BH-5 @ 3.7v coming up sometime later :D

Edit: Another question, how do you find out which pin is which on IC chips?
On some chips it's really clear, with one dot in the corner... But how do you count from there?
Also, some have dots (2 big, one small for instance) in three of the four corners, and pins along all 4 edges... :confused:

[Flak Monkey]

What I don't understand is why lower resistance -> more voltage. How does : Thats because Volts(V)=Amps(I)*Resistence(R). Ohm's law, gotta love it.

[goatman]

not really. usually the switchmode supplies that are used on mobos and inside PSUs use feedback to ckeck if the right voltage is coming out. what we do, is we 'trick' the feedback.

[Entity_Razer]

yhea

when upping the resistance it reads out a lower voltage /more resistance and supply's more volts to compensate IIRC

[Flib]

But when you exlain it you say it like this:

When we set a resistance the Hardware thinks it is supplying too less.
But if this is true we should get more Volts with higher resistance!

[dippyskoodlez]

But when you exlain it you say it like this:

When we set a resistance the Hardware thinks it is supplying too less.
But if this is true we should get more Volts with higher resistance!

we do, dont we? :p:

[craig588]

You are dropping the sense legs resistance to ground. The voltage will take the easiest path, and if it's easier to hit ground rather than going though the regulator the regular will think there isn't enough voltage so it will push it up.

Increasing resistance in the type of mods we do just returns the voltage closer to stock.

[freecableguy]

Ahh! Seems just about no one (except maybe craig588) knows how a vmod works. The component (IC or MOSFET) controls the output voltage based on a sense value. Altering this sense value will cause the circuit to compensate the output voltage up (or down). This raises the voltage to the component being supplied. Don't think that the variable resistor you install has anything to do with the flow of power from the supply to the sink on the board, it doesn't.

[mikead_99]

craig588 and freecableguy are hitting it. @ Flib, some mods actually do increase resistance to reduce the sense voltage (see the MSI Neo2 VDimm mod, VDimm, not VIO as an example) but this is when the resistor is placed in series. The problem with that type mod is you have to find a place to put the resistor and this can often involve cutting a trace or at the least, removing a component. It is generally much easier to find a spot to place a resistor in parallel, in a voltage divider configuration, dividing some of the sense voltage off to ground, reducing the voltage seen by the sense device.

Hope that helps a little.

[Gogar]

Thanks guys! I just read some vmods and wondered how it works.. i was actually in school for electronics at one time... so i should probably have guessed lol but it's been a few years ;)
This also makes me more comfortable about the fact that the trimmers used in some mods were only 0.5 watt.. and i doubt that a gpu uses less than 0.5 watt lol
But i see it doesn't really transfer the power.. thanks for explaining. :)

[heikis]

You are dropping the sense legs resistance to ground. The voltage will take the easiest path, and if it's easier to hit ground rather than going though the regulator the regular will think there isn't enough voltage so it will push it up.


it will push the voltage by upping the current (I)?

http://www.hot.ee/qwerty009/ohm.gif

[Fr3ak]

I thought its something like this:
Soldering a VR to a pin and ground results in a parralel shifted resistor, so the resistance of the whole thing is R(whole thing) = 1/R(pin) + 1/R(VR) , so lowering the resistance of the VR results in a higher voltage according to the formula
U = R * I

I just noticed that I suck in explaining physic stuff in a foreign language.

[ozzimark]

it will push the voltage by upping the current (I)?
not really.. think of an amplifier. in the amplifier circuit, there is a feedback loop that helps the amp know what voltage it's outputting. if you reduce the voltage here, it'll "think" it's not providing enough voltage, and jack up the output until the feedback loop is at the voltage that it "should" be, thus increasing the overall voltage :D

[heikis]

last question: after having the VR installed do I have to set it to max or minimum resistance in order to start tuning from the default voltage? I guess @ max?

[spacemanspliff]

interesting and nice gskill freak!

[uqk]

How voltage modding works. Can't find a voltage mod guide? Read (http://www.ocforums.com/showthread.php?t=264512)

[Revv23]

i knew all this stuff but its a very good refresher and you guys do a good job explaining, so im subscribing.

Thanks fellas.

[wittekakker]

We have Buck convertors used on many of todays hardware. My question, how can the BIOS change a voltage that is set by a buck convertor? For example: Vdimm on our P965 based mainbords.