rafale
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So I was fooling around with my PWM frequency yesterday and was wondering if anyone knows what it really does.
I know an increased frequency increases the temp on the mosfet/VRM but what does it do to the power coming to the CPU? Does it dampen the noise, smoothing the current spikes and oscillations?
I am currently set at 1210MHz on the CPU. Going lower (9XXMHz) leads me to have to increase my Vcore by a couple of notch and even then will not even pass a single LinX/IBT test. If I raise the frequency higher (1333MHz), my computer randomly reboots regardless of CPU load in spite of being LinX stable. Yes! it sometimes reboots even just moving the mouse with no program running in Windows. I am guessing it is a current spike since my temps are all low. The VRM temps hovers in the low 60s.
Also I am wondering if the number of phase on the motherboard has any impact on what the frequency should be as I see other brands of motherboard being limited at 1000MHz but with a lot more power phases (12-16-24).
Turns out this frequency is absolutely critical for my overclock!
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dejanh
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Re:PWM Frequency
2011/04/14 12:23:45
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rafale
So I was fooling around with my PWM frequency yesterday and was wondering if anyone knows what it really does.
I know an increased frequency increases the temp on the mosfet/VRM but what does it do to the power coming to the CPU? Does it dampen the noise, smoothing the current spikes and oscillations?
I am currently set at 1210MHz on the CPU. Going lower (9XXMHz) leads me to have to increase my Vcore by a couple of notch and even then will not even pass a single LinX/IBT test. If I raise the frequency higher (1333MHz), my computer randomly reboots regardless of CPU load in spite of being LinX stable. Yes! it sometimes reboots even just moving the mouse with no program running in Windows. I am guessing it is a current spike since my temps are all low. The VRM temps hovers in the low 60s.
Also I am wondering if the number of phase on the motherboard has any impact on what the frequency should be as I see other brands of motherboard being limited at 1000MHz but with a lot more power phases (12-16-24).
Turns out this frequency is absolutely critical for my overclock!
Really? You managed to drop the Vcore by increasing frequency? Edit: The number of phases has nothing to do with it. Moreover, those tend to be analog phases, these are digital.
post edited by dejanh - 2011/04/14 12:37:16
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Kajimbo
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Re:PWM Frequency
2011/04/14 12:31:25
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dejanh
rafale
So I was fooling around with my PWM frequency yesterday and was wondering if anyone knows what it really does.
I know an increased frequency increases the temp on the mosfet/VRM but what does it do to the power coming to the CPU? Does it dampen the noise, smoothing the current spikes and oscillations?
I am currently set at 1210MHz on the CPU. Going lower (9XXMHz) leads me to have to increase my Vcore by a couple of notch and even then will not even pass a single LinX/IBT test. If I raise the frequency higher (1333MHz), my computer randomly reboots regardless of CPU load in spite of being LinX stable. Yes! it sometimes reboots even just moving the mouse with no program running in Windows. I am guessing it is a current spike since my temps are all low. The VRM temps hovers in the low 60s.
Also I am wondering if the number of phase on the motherboard has any impact on what the frequency should be as I see other brands of motherboard being limited at 1000MHz but with a lot more power phases (12-16-24).
Turns out this frequency is absolutely critical for my overclock!
Really? You managed to drop the Vcore by increasing frequency?
I can confirm this as I have done the same. I was able to drop down my Vcore 2 notches by increasing my PWM from 800Mhz to 940Mhz. But going from 940Mhz to 1210Mhz did nothing. Something you have to play with.
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dejanh
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Re:PWM Frequency
2011/04/14 12:34:14
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Kajimbo
dejanh
rafale
So I was fooling around with my PWM frequency yesterday and was wondering if anyone knows what it really does.
I know an increased frequency increases the temp on the mosfet/VRM but what does it do to the power coming to the CPU? Does it dampen the noise, smoothing the current spikes and oscillations?
I am currently set at 1210MHz on the CPU. Going lower (9XXMHz) leads me to have to increase my Vcore by a couple of notch and even then will not even pass a single LinX/IBT test. If I raise the frequency higher (1333MHz), my computer randomly reboots regardless of CPU load in spite of being LinX stable. Yes! it sometimes reboots even just moving the mouse with no program running in Windows. I am guessing it is a current spike since my temps are all low. The VRM temps hovers in the low 60s.
Also I am wondering if the number of phase on the motherboard has any impact on what the frequency should be as I see other brands of motherboard being limited at 1000MHz but with a lot more power phases (12-16-24).
Turns out this frequency is absolutely critical for my overclock!
Really? You managed to drop the Vcore by increasing frequency?
I can confirm this as I have done the same. I was able to drop down my Vcore 2 notches by increasing my PWM from 800Mhz to 940Mhz. But going from 940Mhz to 1210Mhz did nothing. Something you have to play with.
Sometimes I cringe at the number of variables...I just bumped up my PWM frequency on CPU and VTT by two steps and dropped the Vcore by two steps to see if it will hold up.
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direraptor22
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Re:PWM Frequency
2011/04/14 13:05:17
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Hmmmm.... will have to give it a shot... I never went beyond 800KHz on the PWM
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dejanh
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Re:PWM Frequency
2011/04/14 13:20:28
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Didn't make a difference at first attempt.
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rafale
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Re:PWM Frequency
2011/04/14 14:10:45
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Well, I started from a stable setup. Tried to decrease the frequency to 940MHz and got to a BSOD when running LinX. Notched up the Vcore one notch and got LinX to run but got the wrong residual on the first pass. Two notches and I get 3 passes before I stopped it. Went back and jacked up the frequency to 1333MHz and it passes LinX at my initial voltage but I get random reboots.... Now I am back at 1210MHz. I really wonder what this frequency means.
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fq360
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Re:PWM Frequency
2011/04/14 15:06:43
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i was under the impression that the PWM has to do with power and how clean it is
PWM (Pulse Width Modulation) Frequency allows you to select the frequency range for either higher overclocks or lower power consumption. This feature allows you to have much better manage of your systems performance as well as its power consumption.
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rafale
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Re:PWM Frequency
2011/04/14 16:05:11
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Yes, I read this but I was looking for something more detailed. What does it do to the power waveform? How does it affect the stability of the power. etc...
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direraptor22
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Re:PWM Frequency
2011/04/14 16:22:52
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My board only allows 800, 933, 1067KHz PWM frequencies... E758
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kingofsorrow
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Re:PWM Frequency
2011/04/14 16:29:38
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I'm runnning them at max. The cleaner energy the better.
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ty_ger07
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Re:PWM Frequency
2011/04/14 16:35:21
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rafale
Yes, I read this but I was looking for something more detailed. What does it do to the power waveform? How does it affect the stability of the power. etc...
The power output to the CPU is the result of all the power phases combined after they are filtered. The output power will still have residual "noise" (ripple) and won't be a perfectly smooth solid voltage potential. Increasing the PWM frequency helps smooth out the output voltage and decrease ripple since shorter duration voltage spikes are more easily filtered. The side effect is that the VRM temperature will increase since their duty cycle is increased.
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rafale
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Re:PWM Frequency
2011/04/14 17:45:47
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ty_ger07
rafale
Yes, I read this but I was looking for something more detailed. What does it do to the power waveform? How does it affect the stability of the power. etc...
The power output to the CPU is the result of all the power phases combined after they are filtered. The output power will still have residual "noise" (ripple) and won't be a perfectly smooth solid voltage potential. Increasing the PWM frequency helps smooth out the output voltage and decrease ripple since shorter duration voltage spikes are more easily filtered. The side effect is that the VRM temperature will increase since their duty cycle is increased.
Thanks, I don't have enough background on how the power phase work and how the PWM intervenes so I guess I will look into it. It sounds like the PWM is a closed loop monitor of the voltage? Increasing its frequency increases how frequently it corrects the voltage?
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ty_ger07
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Re:PWM Frequency
2011/04/14 17:58:01
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☄ Helpful
rafale
ty_ger07
rafale
Yes, I read this but I was looking for something more detailed. What does it do to the power waveform? How does it affect the stability of the power. etc...
The power output to the CPU is the result of all the power phases combined after they are filtered. The output power will still have residual "noise" (ripple) and won't be a perfectly smooth solid voltage potential. Increasing the PWM frequency helps smooth out the output voltage and decrease ripple since shorter duration voltage spikes are more easily filtered. The side effect is that the VRM temperature will increase since their duty cycle is increased.
Thanks, I don't have enough background on how the power phase work and how the PWM intervenes so I guess I will look into it. It sounds like the PWM is a closed loop monitor of the voltage? Increasing its frequency increases how frequently it corrects the voltage?
You have 12v input to the motherboard via the 8-pin CPU power connector. The PWM controls the on-off cycle of the VRMs which simply switch on and off the 12v supply. The desired CPU voltage is attained by briefly turning on 12v power. If the VRMs were on all the time, the CPU would run on 12v, which is obviously way too much for the CPU to handle. Consider this: Let's say you turn a light switch on and off very rapidly. Let's say that the input to the light switch is 12v and you turn it on and off at a rate that it is on 50% of the time and off 50% of the time per second. This would be called a 50% duty cycle and the resultant voltage after filtering would be 6v. The attain 1.2v to the CPU, the on duty cycle would have to be around 10% of the the total second. As you can understand, the voltage requires filtering to result in an average voltage of 1.2v. If there were no filtering, the CPU would receive 12v for 1/10th of a second, and then no voltage for 9/10 of a second. Obviously that wouldn't work. So the voltage is stabilized by capacitors which store the voltage for the remainder of the off cycle and absorb the voltage spike during the period that the VRM is "on". PWM frequency simply controls how rapidly the VRM can turn on and off. The actual on/off duty cycle will still ultimately be controlled by your desired voltage setting. By this analogy, you would think that PWM frequency would not change the duty cycle of the VRMs, but it does. Why? As the PWM frequency increases, the inductance of the inductors increases which effectively increases the required voltage outputs of the VRMs to overcome the increase in inductance which therefore increases the VRM duty cycle.
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rafale
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Re:PWM Frequency
2011/04/14 18:30:21
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Thank you very much!
Ok Now I understand it works like the PWM fans except that it uses capacitors for high frequency filtering.
I have an engineering background but I am not an EE.
What then do the power phase number signify? Are they alternate circuits through which the 12V go through in order to prevent overheat?
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I_Know_God
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Re:PWM Frequency
2011/04/14 22:19:40
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+1 more tech porn subed
i might as well add to this, i have more or less heard that 100c is perfectly acceptable safe(upper limit) temps for the vreg and mosfet chips everyone still agree with this, and what kind of temps are you getting?
im getting 81c idle on 768 x58sli, i think this is mainly due to it not getting air because of my h70
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ty_ger07
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Re:PWM Frequency
2011/04/14 22:23:52
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☄ Helpful
rafale
Thank you very much!
Ok Now I understand it works like the PWM fans except that it uses capacitors for high frequency filtering.
I have an engineering background but I am not an EE.
What then do the power phase number signify? Are they alternate circuits through which the 12V go through in order to prevent overheat?
Yeah, basically. All the VRM phases are in parallel with eachother and out of phase with eachother. The reason why they are out of phase is to help stabilize the voltage output so that when some phases are outputting nothing, another phase has an output. And the reason why there is more than one phase and the reason why they are in parallel is to increase the wattage output capability and prevent an individual phase from overheating. Another cool thing about the design is that if one individual VRM in a single phase is running hotter than the other VRMs, its output will automatically be reduced and the other phases will work harder. This stabilizes the VRM temperatures so that they are more equal and reduces the likelihood of a single VRM from overheating and burning out.
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rafale
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Re:PWM Frequency
2011/04/14 22:55:34
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Ok now I understand how it works. Thanks!
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