The symbols and basic construction for both configurations of MOSFETs are shown below. The enhancement mode MOSFET is equivalent to a “Normally Open” switch. Enhancement Type – the transistor requires a Gate-Source voltage, ( V GS ) to switch the device “ON”.The depletion mode MOSFET is equivalent to a “Normally Closed” switch. Depletion Type – the transistor requires the Gate-Source voltage, ( V GS ) to switch the device “OFF”.The main difference this time is that MOSFETs are available in two basic forms: Like the previous JFET tutorial, MOSFETs are three terminal devices with a Gate, Drain and Source and both P-channel (PMOS) and N-channel (NMOS) MOSFETs are available. Also like the JFET, the MOSFETs very high input resistance can easily accumulate large amounts of static charge resulting in the MOSFET becoming easily damaged unless carefully handled or protected. The isolation of the controlling Gate makes the input resistance of the MOSFET extremely high way up in the Mega-ohms ( MΩ ) region thereby making it almost infinite.Īs the Gate terminal is electrically isolated from the main current carrying channel between the drain and source, “NO current flows into the gate” and just like the JFET, the MOSFET also acts like a voltage controlled resistor where the current flowing through the main channel between the Drain and Source is proportional to the input voltage. This ultra thin insulated metal gate electrode can be thought of as one plate of a capacitor. The IGFET or MOSFET is a voltage controlled field effect transistor that differs from a JFET in that it has a “Metal Oxide” Gate electrode which is electrically insulated from the main semiconductor n-channel or p-channel by a very thin layer of insulating material usually silicon dioxide, commonly known as glass. The most common type of insulated gate FET which is used in many different types of electronic circuits is called the Metal Oxide Semiconductor Field Effect Transistor or MOSFET for short. The MOSFET is a type of semiconductor device called an Insulated Gate Field Effect Transistor. As well as the Junction Field Effect Transistor (JFET), there is another type of Field Effect Transistor available whose Gate input is electrically insulated from the main current carrying channel.

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