MOSFET

What is a MOSFET?​

MOSFET or Metal Oxide Semiconductor Field Effect Transistor also called as voltage controlled device acts as an amplifier and a switch. It amplifies only DC voltage and not AC. It is the common FET. It is formed of semiconductor material like silicon and germanium. It is denoted by Q, PQ and also U.

Types of MOSFET used in laptops:​

There are two types of MOSFET based on the channel as N-channel and P-channel MOSFET.
There are 6 types based on their package as standard, SO-8, SOT-8, SOT-6, Dual channel SO-8 and Dual channel SOT-6 packages



When a voltage is applied to the gate, MOSFET turns ON and the drain (on/off) is connected to the source and this connection is capable of switching high current (flow of electrons) through the MOSFET, the gate requires virtually no power to turn ON the MOSFET.

Pinout Identification of MOSFETT used in recent Laptops






8 Legs and Dual MOFETS


P-Channel Mosfet in laptop motherboard used in charging and DC circuits jack section, which functions as protection circuit to close or passed the voltage of 19V/S5 circuit, while outside the bypass line DC jack and charging, this component is not in use. In the input voltage circuit and any output, the value is the same except the gate which is ½ value of input and output values (generally) although not all of them like that. Because the characteristic of this component decided payload and only move on the positive track which works as ordered from the gate between pass the voltage or not (switch).

So, if this component is damage, the input will find the voltage and at the output do not find any voltage. With the condition on the gate there is voltage.

In addition, the protection system will be active if there is a short in the output path after the charging circuit, result the voltage is only at the Mosfet input only (but the Mosfet is good condition). So, do not directly change the Mosfet, mainly on total dead short damage. First make sure the output path of the Mosfet is not the short way by measuring the diode value mode (buzzer).

The red probe on the output leg of the Mosfet and black probe on ground, and if it beeps sound, can be sure there are short in output after Mosfet, especially on VIN path.

N-channel in laptop motherboard is many used as lowering voltage and Current amplifier in the process of switching (step down) inside switching/SMPS circuit. This component often found and in use for VRAM circuit, VCC CORE, GPU CORE, 3V &5V.

N-channel and P-channel Mosfet Characteristic:​

Mosfet P-channel is often found in DC jack and Charging circuits. Character and the function of this component serve as a protection circuit.

Example below:
if there is short after output pin 5678 then automatically gate on, PIN 4 will open the gate as ordered from SYSTEM, consequently the voltage is only present on pin 123 only. And if not found short circuit on the output then 90% certainly this Mosfet is problematic. And other problems are also sourced from Mosfet underneath (we call it a small transistor 6 leg).



N-Channel Mosfet in parallel arrangement (HIGH & LOW), on a continuous basis simple, works for the switching process that its function is for decrease voltage according to gate command voltage from DC or IC 3V & 5V. This is the conclusion of the difference of N-channel and p-channel Mosfet. If N-channel is identical to parallel circuit while P-Channel identical to the series.

Consider one of the legs of the MOSFET that connected to the ground. If this component is damaged, consequently SHORT CIRCUIT, even the damaged underneath or above the Mosfet. Gate on the N-channel Mosfet is rarely problematic, because in this path there is no component to pass (toll roads). Except, the absence of gate or command voltage of the controller itself in this case IC 3V & 5V problem.


Enough with the introduction to Mosfets. We'll conduct the testing process and see which MOSFET is working and which isn't.

How to check Mosfet:​

First we'll check if this Mosfet is an N-Channel or P-Channel, set multimeter to Buzzer mode.

N-Channel Mosfet :
Connect the black probe to the drain and the red probe to the source of the Mosfet, and if you get a value on the screen of Multimeter then this Mosfet is N-Channel.



P-Channel Mosfet :
Connect the Red probe to drain and Black probe to the source and if you get a value then it’s a P-Channel Mosfet.


How to know if is defective. First turn ON digital multimeter and set to Diode mode and connect the red lead to source "S" and connect the black lead to drain "D" the multimeter should indicate the OL mark.



Now reverse the leads put the black lead to the source "S" and the red lead is to drain "D",
the multimeter should have reading between 0.45-0.7