MOSFET datasheets don’t contain these types of specs; instead, a MOSFET is an abstract concept that has certain general behaviors. Manufacturers endeavor to maintain these behaviors, and often publish separate application notes about them. For example: IR AN1084 Power MOSFET Basics; IR AN936 The Do’s and Don’ts of Using MOS-Gated Transistors. Power MOSFET is a type of MOSFET which is specially meant to handle high levels of power. These exhibit high switching speed and can work much better in comparison with other normal MOSFETs in the case of low voltage levels. MOSFET is an acronym for Metal Oxide Semiconductor Field Effect Transistor.It is a type of FET (Field Effect Transistor) that has an insulated metal oxide layer between its gate and channel. On the contrary, JFETs gate is connected with its channel. This type of MOSFET is fabricated on a p-type semiconductor substrate. The complementary MOSFET is the p-type or p-channel MOSFET. It contains p-type source and drain regions in an n-type substrate. The inversion layer is formed when holes are attracted to the interface by a negative gate voltage. While the holes still flow from source to drain. In field-effect transistors (FETS), depletion mode and enhancement mode are two major transistor types, corresponding to whether the transistor is in an ON state or an OFF state at zero gate-source voltage. Enhancement-mode MOSFETS (metal–oxide–semiconductor FETs) are the common switching elements in most integrated circuits.

• Types Of Mosfet Transistor
• Types Of Mosfet Amplifiers
• Types Of Mosfet
• Types Of Fets

In field-effect transistors (FETS), depletion mode and enhancement mode are two major transistor types, corresponding to whether the transistor is in an ON state or an OFF state at zero gate-source voltage.

Enhancement-mode MOSFETS (metal–oxide–semiconductor FETs) are the common switching elements in most integrated circuits. These devices are off at zero gate–source voltage. NMOS can be turned on by pulling the gate voltage higher than the source voltage, PMOS can be turned on by pulling the gate voltage lower than the source voltage. In most circuits, this means pulling an enhancement-mode MOSFET's gate voltage towards its drain voltage turns it ON.

In a depletion-mode MOSFET, the device is normally ON at zero gate–source voltage. Such devices are used as load 'resistors' in logic circuits (in depletion-load NMOS logic, for example). For N-type depletion-load devices, the threshold voltage might be about –3 V, so it could be turned off by pulling the gate 3 V negative (the drain, by comparison, is more positive than the source in NMOS). In PMOS, the polarities are reversed.

The mode can be determined by the sign of the threshold voltage (gate voltage relative to source voltage at the point where an inversion layer just forms in the channel): for an N-type FET, enhancement-mode devices have positive thresholds, and depletion-mode devices have negative thresholds; for a P-type FET, enhancement-mode negative, depletion-mode positive.

Junction field effect - transistors (JFETs) are depletion mode, since the gate junction would forward bias if the gate were taken more than a little from source toward drain voltage. Such devices are used in gallium arsenide and germanium chips, where it is difficult to make an oxide insulator.

Alternative terminology[edit]

Some sources say 'depletion type' and 'enhancement type' for the device types as described in this article as 'depletion mode' and 'enhancement mode', and apply the 'mode' terms for which direction the gate–source voltage differs from zero.^[1] Moving the gate voltage toward the drain voltage 'enhances' the conduction in the channel, so this defines the enhancement mode of operation, while moving the gate away from the drain depletes the channel, so this defines depletion mode.

Enhancement-load and depletion-load logic families[edit]

Depletion-load NMOS logic refers to the logic family that became dominant in silicon VLSI in the latter half of the 1970s; the process supported both enhancement-mode and depletion-mode transistors, and typical logic circuits used enhancement-mode devices as pull-down switches and depletion-mode devices as loads, or pull-ups. Logic families built in older processes that did not support depletion-mode transistors were retrospectively referred to as enhancement-load logic, or as saturated-load logic, since the enhancement-mode transistors were typically connected with gate to the V_DD supply and operated in the saturation region (sometimes the gates are biased to a higher V_GG voltage and operated in the linear region, for a better power–delay product (PDP), but the loads then take more area).^[2] Alternatively, rather than static logic gates, dynamic logic such as four-phase logic was sometimes used in processes that did not have depletion-mode transistors available.

For example, the 1971 Intel 4004 used enhancement-load silicon-gate PMOS logic, and the 1976 Zilog Z80 used depletion-load silicon-gate NMOS.

History[edit]

The first MOSFET (metal-oxide-semiconductor field-effect transistor) demonstrated by Egyptian engineer Mohamed M. Atalla and Korean engineer Dawon Kahng at Bell Labs in 1960 was an enhancement mode siliconsemiconductor device.^[3] In 1963, both depletion and enhancement mode MOSFETs were described by Steve R. Hofstein and Fred P. Heiman at RCA Laboratories.^[4] In 1966, T.P. Brody and H.E. Kunig at Westinghouse Electric fabricated enhancement and depletion mode indium arsenide (InAs) MOS thin-film transistors (TFTs).^[5][6]

References[edit]

1. ^John J. Adams (2001). Mastering Electronics Workbench. McGraw-Hill Professional. p. 192. ISBN978-0-07-134483-8.
2. ^Jerry C. Whitaker (2005). Microelectronics (2nd ed.). CRC Press. p. 6-7–6-10. ISBN978-0-8493-3391-0.
3. ^Sah, Chih-Tang (October 1988). 'Evolution of the MOS transistor-from conception to VLSI'(PDF). Proceedings of the IEEE. 76 (10): 1280–1326 (1293). doi:10.1109/5.16328. ISSN0018-9219.
4. ^Hofstein, Steve R.; Heiman, Fred P. (September 1963). 'The silicon insulated-gate field-effect transistor'. Proceedings of the IEEE. 51 (9): 1190–1202. doi:10.1109/PROC.1963.2488.
5. ^Woodall, Jerry M. (2010). Fundamentals of III-V Semiconductor MOSFETs. Springer Science & Business Media. pp. 2–3. ISBN9781441915474.
6. ^Brody, T. P.; Kunig, H. E. (October 1966). 'A HIGH‐GAIN InAs THIN‐FILM TRANSISTOR'. Applied Physics Letters. 9 (7): 259–260. doi:10.1063/1.1754740. ISSN0003-6951.

Let’s talk about the basics of MOSFET and how to use them. This tutorial is written primarily for non-academic hobbyists, so I will try to simplify the concept and focus more on the practical side of things.

However if you are into how MOSFET work, I will share some useful academic articles and resources at the end of this post. MOSFET has some advantage and disadvantage over BJT, so choose carefully base on your application.

You can buy MOSFET’s for Arduino Projects on Amazon: http://amzn.to/2Gk6ruW

Types Of Mosfet Transistor

MOSFET stands for metal-oxide semiconductor field-effect transistor. It is a special type of field-effect transistor (FET).

Unlike BJT which is ‘current controlled’, the MOSFET is a voltage controlled device. The MOSFET has “gate“, “Drain” and “Source” terminals instead of a “base”, “collector”, and “emitter” terminals in a bipolar transistor. By applying voltage at the gate, it generates an electrical field to control the current flow through the channel between drain and source, and there is no current flow from the gate into the MOSFET.

A MOSFET may be thought of as a variable resistor, where the Gate-Source voltage difference can control the Drain-Source Resistance. When there is no applying voltage between the Gate-Source , the Drain-Source resistance is very high, which is almost like a open circuit, so no current may flow through the Drain-Source. When Gate-Source potential difference is applied, the Drain-Source resistance is reduced, and there will be current flowing through Drain-Source, which is now a closed circuit.

In a nutshell, a FET is controlled by the Gate-Source voltage applied (which regulates the electrical field across a channel), like pinching or opening a straw and stopping or allowing current flowing. Because of this property, FETs are great for large current flow, and the MOSFET is commonly used as a switch.

Okay, let me summarize the differences between BJT and MOSFET.

• Unlike bipolar transistors, MOSFET is voltage controlled. While BJT is current controlled, the base resistor needs to be carefully calculated according to the amount of current being switched. Not so with a MOSFET. Just apply enough voltage to the gate and the switch operates.
• Because they are voltage controlled, MOSFET have a very high input impedance, so just about anything can drive them.
• MOSFET has high input impedence.

To use a MOSFET as a switch, you have to have its gate voltage (Vgs) higher than the source. If you connect the gate to the source (Vgs=0) it is turned off.

For example we have a IRFZ44N which is a “standard” MOSFET and only turns on when Vgs=10V – 20V. But usually we try not to push it too hard so 10V-15V is common for Vgs for this type of MOSFET.

Types Of Mosfet Amplifiers

However if you want to drive this from an Arduino which is running at 5V, you will need a “logic-level” MOSFET that can be turned on at 5V (Vgs = 5V). For example, the ST STP55NF06L. You should also have a resistor in series with the Arduino output to limit the current, since the gate is highly capacitive and can draw a big instantaneous current when you try to turn it on. Around 220 ohms is a good value.

This page shows some detail explanation how a MOSFET works as a switch. This page shows some advanced usage of MOSFET.

MOSFETs come in four different types. There are three main categories we need to know.

• N-Channel (NMOS) or P-Channel (PMOS)
• Enhancement or Depletion mode
• Logic-Level or Normal MOSFET

N-Channel – For an N-Channel MOSFET, the source is connected to ground. To turn the MOSFET on, we need to raise the voltage on the gate. To turn it off we need to connect the gate to ground.

P-Channel – The source is connected to the power rail (Vcc). In order to allow current to flow the Gate needs to be pulled to ground. To turn it off the gate needs to be pulled to Vcc.

Types Of Mosfet

Depletion Mode – It requires the Gate-Source voltage ( Vgs ) applied to switch the device “OFF”.

Enhancement Mode – The transistor requires a Gate-Source voltage ( Vgs ) applied to switch the device “ON”.

Despite the variety, the most commonly used type is N-channel enhancement mode.

There are also Logic-Level and Normal MOSFET, but the only difference is the Gate-Source potential level required to drive the MOSFET.

I will try to explain it in the simplest way I can, for more detail or if you are in doubt, check the references and links I provide at the bottom of the post.

Types Of Fets

MOSFET is a voltage controlled field effect transistor that differs from a JFET. The Gate electrode is electrically insulated from the main semiconductor by a thin layer of insulating material (glass, seriously!). This insulated metal gate is like a plate of a capacitor which has an extremely high input resistance (as high as almost infinite!). Because of the isolation of the Gate there is no current flow into the MOSFET from Gate.

When voltage is applied at the gate, it changes the width of the Drain-Source channel along which charge carriers flow (electron or hole). The wider the channel, the better the device conducts.

The MOSFET are used differently compared to the conventional junction FET.

• The infinite high input impedance makes MOSFETs useful for power amplifiers. The devices are also well suited to high-speed switching applications. Some integrated circuits contain tiny MOSFETs and are used in computers.
• Because the oxide layer is so thin, the MOSFET can be damaged by built up electrostatic charges. In weak-signal radio-frequency work, MOSFET devices do not generally perform as well as other types of FET.

Where to put the load to a MOSFET? Source or Drain?

Because load has resistance, which is basically a resitor. For N-channel MOSFET the reason we usually put the load at the Drain side is because of the Source is usually connected to GND.

If load is connected at the source side, the Vgs will needs to be higher in order to switch the MOSFET, or there will be insufficient current flow between source and drain than expected.

Heat Sink connected to the Drain?

Typically the heat sink on the back of a MOSFET is connected to the Drain! If you mount multiple MOSFETs on a heat sink, they must be electrically isolated from the heat sink! It’s good practice to isolate regardless in case the heat sink is bolted to a grounding frame.

What is the Body Diode For?

MOSFETs also have an internal diode which may allow current to flow unintentionally. The body diode will also limit switching speed. You don’t have to worry about it if you are operating under 1Mhz.

• Theory behind MOSFET (Youtube Video Lecture)