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آموزشی: چگونگی تست ماسفت های مادربرد به زبان اصلی

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[h=1]What is a MOSFET, what does it look like, and how does it work?[/h]
Author: W1zzard
Date: 2004-05-24 07:11:14​


Pronounced MAWS-feht. Acronym for metal-oxide semiconductor field-effect transistor. These are used in many scenarios where you want to convert voltages. On your motherboard for example to generate CPU Voltage, Memory Voltage, AGP Voltage etc.
Mosfets are usually used in pairs. If you see six mosfets around your CPU socket you have three-phase power.
[h=3]Technical Info[/h]
MOSFETs come in four different types. They may be enhancement or depletion mode, and they may be n-channel or p-channel. For this application we are only interested in n-channel enhancement mode MOSFETs, and these will be the only ones talked about from now on. There are also logic-level MOSFETs and normal MOSFETs. The only difference between these is the voltage level required on the gate.

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Unlike bipolar transistors that are basically current-driven devices, MOSFETs are voltage-controlled power devices. If no positive voltage is applied between gate and source the MOSFET is always non-conducting. If we apply a positive voltage UGS to the gate we'll set up an electrostatic field between it and the rest of the transistor. The positive gate voltage will push away the 'holes' inside the p-type substrate and attracts the moveable electrons in the n-type regions under the source and drain electrodes. This produces a layer just under the gate's insulator through which electrons can get into and move along from source to drain. The positive gate voltage therefore 'creates' a channel in the top layer of material between oxide and p-Si. Increasing the value of the positive gate voltage pushes the p-type holes further away and enlarges the thickness of the created channel. As a result we find that the size of the channel we've made increases with the size of the gate voltage and enhances or increases the amount of current which can go from source to drain- this is why this kind of transistor is called an enhancement mode device.

More info here: http://homepages.which.net/~paul.hills/SpeedControl/Mosfets.html
[h=3]MOSFET testing[/h]
Get a multimeter with a diode test range.
Connect the meter negative to the MOSFET's source.
Hold the MOSFET by the case or the tab if you wish, it doesn't matter if you touch the metal body but be careful not to touch the leads until you need to. Do NOT allow a MOSFET to come in contact with your clothes, plastic or plastic products, etc. because of the high static voltages it can generate.
First touch the meter positive on to the gate.
Now move the positive meter probe to the drain. You should get a low reading. The MOSFET's gate capacitance has been charged up by the meter and the device is turned on.
With the meter positive still connected to the drain, touch a finger between source and gate (and drain if you wish, it doesn't matter). The gate will be discharged through your finger and the meter reading should go high, indicating a non-conducting device.​


 

pese

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In the computer enthusiast world the terms are not fully defined. The most used meanings are following:
VCore: The core supply voltage of an 'important' chip like your CPU or GPU, usually not the Northbridge. Most frequently used to indicate CPU voltage.
VDD: The supply voltage to your Northbridge chip or the supply voltage for the input buffers and core logic of your memory chips (mostly on graphic cards).
VDDQ: The supply voltage to the output buffers of a memory chip.
VTT: Tracking Termination Voltage. Compared to VREF to determine Hi/Lo
VMem: Supply voltage to a memory chip.
VDDR, VDimm: Supply voltage to the memory on your motherboard.
VRef: Reference voltage for the input lines of a chip that determines the voltage level at which the threshold between a logical 1 and a logical 0 occurs. Usually 1/2 VDDQ.
VGPU: The supply voltage to your graphic card's processor.
[h=3]Terms used by ATI internally:[/h]
VDDC: GPU Voltage
MVDDC: Memory Core Logic Voltage
MVDDQ: Memory Voltage supplied to the output buffers of the video card memory.
VTT: Termination Tracking voltage for video card memory.
[h=3]Electrical Engineering Information[/h]
Positive voltages:
Vcc- Positive supply voltage of a Bipolar Junction Transistor.
Vdd- Positive supply voltage of A Field Effect Transistor

Negative voltages/ground:
Vee- Negative supply voltage of a Bipolar Junction Transistor.
Vss- Negative supply voltage of A Field Effect Transistor.

The letters c,d,e and s originated from the name of the legs of the transistors Collector, Drain, Emitter and Source.

The absolute distinctions between these common supply terms has since been blurred by the interchangeable application of TTL and CMOS logic families. Most CMOS (74HC / AC, etc.) IC data sheets now use Vcc and Gnd to designate the positive and negative supply pins.

The doubled suffix indicates that the voltage is "common", i.e. it is the supply voltage to one or more collectors (in the case of cc) and not just the voltage at a specific collector. Similarily, Vee is a common voltage for all emitters etc.
 
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pese

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این هم یک مقاله در رابطه با مدار فرکانس ساز برای مادربرد
[h=1]What is a PLL?[/h]

[h=1]What is a PLL?[/h]
Author: W1zzard​
Date: 2004-05-24 07:09:03​


A phase-locked loop (PLL) is an electronic circuit with a voltage- or current-driven oscillator that is constantly adjusted to match in phase (and thus locked on) the frequency of an input signal. PLLs are used for frequency control. They can be configured as frequency multipliers, dividers, demodulators, tracking generators or clock recovery circuits.

On a computer motherboard a PLL is used to generate several frequencies that are required for proper operation:

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Let's try to build our own PLL: What we want is a stable frequency that we can change on the fly.
A crystal oscillator would give us a stable frequency- but it's fixed and using several oscillators would be a waste of resources.
If we use a VCO (Voltage Controlled Oscillator) we get a freely changeable frequency but the frequency would change even at the slightest variation of voltage. If there was a way to combine the stability of the crystal oscillator with the flexibility of the VCO we would have the perfect solution for our problem.

What if we add a phase detector? A phase detector is a device that takes two signals. If both have the same phase and frequency the output is zero. If the signals are out-of-phase the output will be a DC voltage that is proportional to the phase difference between the two inputs.

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What does this do? The crystal generates a frequency of 10 MHz in our example. This frequency gets fed to the PD. The VCO output is zero right now so the PD output is high because the frequencies differ a lot. The PD output gets fed into the VCO and generates a frequency. This goes back to the PD and so on - eventually the VCO will lock onto the frequency of the crystal. And the output of the VCO will be 10 MHz. This is a basic PLL circuit.
Now you ask where's the flexibility? What we have right now is equivalent to a crystal oscillator!

Let's see.. We want an output of 20 Mhz for this example. What we do now is add a divide-by-two counter between the VCO output and the PD. This 'tricks' the PD into thinking our output frequency is only the half of what it really is- so it starts regulating the voltage to the VCO. Voila 20 MHz. If we used a programmable divider here we could change frequencies on the fly.

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Now we can multiply frequencies by integer values. But how can we multiply our frequency by fractional values or divide it?
For example we want 10 Mhz x 3.5 for an output of 35 Mhz. This is done by adding another pre-divider [whats the correct term here?] between the crystal and the PD. In our example we could use a pre-divider of 2 and a divider of 7. Our output would be 10 Mhz / 2 * 7 = 35 MHz.

This is our PLL in all its goodness:

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The added loop filter is not required for general understanding. It's here for completeness. The loop filter is designed to match the characteristics required by the application of the PLL. For example, it determines how fast the signal frequency can change and still maintain lock. This is the maximum slewing rate. The narrower the loop filter bandwidth the smaller the achievable phase error. This comes at the expense of slower response and reduced capture range.

 

pese

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[h=2]How To Test A Motherboard Thru Their VRMs[/h]
In Uncategorized on May 13, 2012 at 6:12 am

Voltage Regulator Modules (VRMs)
VRMs (voltage regulator modules) are a specific class of MOSFETs;​
“Far from being true. A VRM module consists of the controlling IC and MosFet’s (if we focus only on semiconductors).
However, it is true that there are many type of FET’s. MOSFET being the most common one. JFET is one of the other type.​
 
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