Slkormicro takes you to understand MOSFET

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2022-03-17 01:18:08 95

What is an enhanced MOS tube? What is an enhancement mode MOS tube? What is a depletion mode MOS tube

Enhancement: When no voltage is applied between the gate and the substrate, there is no channel under the gate. That is, for NMOS, the threshold voltage is greater than 0; for PMOS, it is less than 0. Depletion mode: When no voltage is applied between the gate and the substrate, there is a channel under the gate. That is, for NMOS, the threshold voltage is less than 0; for PMOS, it is greater than 0. By changing the doping concentration of the active region, controlling the thickness of the gate insulating layer and selecting a gate material with a certain work function, enhancement or depletion MOSFETs can be fabricated.

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What are the precautions for MOS tubes?

(3) Due to the extremely high input impedance of MOS field effect transistors, the lead pins must be short-circuited during transportation and storage, and metal shielding should be used to prevent the grid from being broken down by external induced potential.

What is MOS tube?

MOS tubes are generally called field effect transistors. Unlike diodes and triodes, diodes can only pass forward current and reverse cutoff and cannot be controlled. In general, triodes are amplified from small currents to controlled large currents. MOS tubes are controlled by small voltages. current.

The input resistance of the MOS tube is very large, the megohm level, easy to drive, but the price is higher than that of the triode, generally suitable for the situation that requires a small voltage to control a large current, the induction cooker is generally used 20A or 25A field effect tube.

Expansion information:

The characteristics of MOS capacitors can be used to form MOS transistors. Gate, dielectric and backgate remain as they are. On either side of the GATE are two additional selectively doped regions. One of them is called source and the other is called drain. Assume that both source and backgate are grounded, and drain is connected to a positive voltage. MOS tubes are generally called field effect transistors. Unlike diodes and triodes, diodes can only pass forward current and reverse cutoff and cannot be controlled. In general, triodes are amplified from small currents to controlled large currents. MOS tubes are controlled by small voltages. Current, the input resistance of MOS tube is very large, megohm level, easy to drive, but the price is higher than that of triode, generally suitable for the situation that needs small voltage to control large current, the field effect of 20A or 25A is generally used in induction cooker Tube. The mos tube is a metal-oxide-semiconductor field effect transistor, or a metal-insulator-semiconductor. The source and drain of the MOS tube can be reversed, and they are all N-type regions formed in the P-type backgate. In most cases, these two regions are the same, even if the two ends are reversed, it will not affect the performance of the device. Such devices are considered symmetrical.

The bipolar transistor amplifies the small change of the current at the input end and outputs it at the output end

a large current change. The gain of a bipolar transistor is defined as the ratio of output to input current (beta). Another type of transistor, called a field effect transistor (FET), converts changes in input voltage into changes in output current. The gain of a FET is equal to its transconductance, defined as the ratio of the change in output current to the change in input voltage. The most common ones on the market are N-channel and P-channel. For details, refer to the picture on the right (N-channel depletion MOS transistor). The common P-channel is a low-voltage Mos tube.

The FET's name also comes from its input (called the gate) through the projection

An electric field on an insulating layer affects the current flowing through the transistor. In fact no current flows through this insulator, so the gate current of the FET is very small. The most common FET uses a thin layer of silicon dioxide as the insulator under the GATE. Such transistors are called metal-oxide-semiconductor (MOS) transistors, or, metal-oxide-semiconductor field effect transistors (MOSFETs). Because MOS tubes are smaller and more power efficient, they have replaced bipolar transistors in many applications. what is mos tube

The role of mos tube

The role of the MOS tube The MOS tube is a voltage-controlled element. You only need to add the required voltage to its voltage-controlled element to turn it on. Its conduction is like a transistor in a saturated state, and the voltage drop of the conduction junction is the smallest. This is often said that the classic is the switching effect. If the control voltage is removed, it will be cut off. The full English name of the MOS tube MOS tube is called MOSFET (MetalOxideSemiconductorFieldEffectTransistor), which is a metal oxide semiconductor type field effect transistor, which belongs to the insulating gate of the field effect transistor. type. Therefore, MOS transistors are sometimes called field effect transistors. In general electronic circuits, MOS tubes are usually used in amplifier circuits or switch circuits. In the power supply voltage regulator circuit on the motherboard, the role of the MOSFET is mainly to judge the potential, which is often represented by "Q" plus a number on the motherboard. 1. What is the function of MOS tube? At present, there are not too many MOS tubes used on motherboards or graphics cards, usually about 10. The main reason is that most of the MOS tubes are integrated into IC chips. Since the MOS tube mainly provides stable voltage for accessories, it is generally used near the CPU, AGP slot and memory slot. Among them, a group of MOS tubes are arranged near the CPU and AGP slots, while a group of MOS tubes is shared by the memory slot. The MOS tubes generally appear on the motherboard in the form of a group of two. 2. What are the performance parameters of the MOS tube? High-quality MOS tubes can withstand higher current peaks. Under normal circumstances, we need to judge the quality of the MOS tube on the motherboard, and we can see the maximum current value it can withstand. There are many parameters that affect the quality of MOS tubes, such as extreme current and extreme voltage. However, so many parameters cannot be marked on the MOS tube, so generally only the model of the product is marked on the surface of the MOS tube. We can search for specific performance parameters on the Internet according to the model. It should also be noted that temperature is also a very important performance parameter of MOS tubes. It mainly includes ambient temperature, tube shell temperature, storage temperature, etc. As the CPU frequency increases, the current that the MOS tube needs to withstand also increases, and it is very common to provide a current of nearly 100 A. Of course, the heat generated when such a huge current passes through makes the MOS tube "fever". For the safety of MOS tubes, high-quality motherboards have also begun to install heat sinks for MOS tubes. How do inductors and MOS tubes work together? Through the above introduction, we know that the MOS tube plays a role in regulating the entire power supply system, but the MOS tube cannot be used alone. It must be combined with the inductor coil, capacitor, etc. to form a filter voltage regulator circuit to give full play to its advantages. The PWM (PlusWidthModulator, pulse width modulator) chip on the motherboard generates a pulse waveform with an adjustable width, so that the two MOS tubes can be turned on in turn. When the voltage at both ends of the load (such as the voltage required by the CPU) is to be reduced, the switching effect of the MOS tube begins to take effect, and the external power supply charges the inductor and reaches the required rated voltage. When the voltage at both ends of the load rises, the external power supply is disconnected through the switching action of the MOS tube, and the inductor releases the energy just charged. At this time, the inductor becomes a "power supply" and continues to supply power to the load. With the continuous consumption of the stored energy on the inductor, the voltage across the load begins to gradually decrease, and the external power supply needs to be charged again through the switching action of the MOS tube. In this way, the process of charging and discharging is continuously carried out, thereby forming a stable voltage, so that the voltage across the load will never increase or decrease.

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Slkormicro takes you to understand MOSFET

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