vortibravo.blogg.se - Igfet transistor power transistor

Both the p-channel and the n-channel MOSFETs are available in two basic forms, the Enhancement type and the Depletion type. This makes the MOSFET device especially valuable as electronic switches or to make logic gates because with no bias they are normally non-conducting and this high gate input resistance means that very little or no control current is needed as MOSFETs are voltage controlled devices. With a insulated gate MOSFET device no such limitations apply so it is possible to bias the gate of a MOSFET in either polarity, positive ( +ve) or negative ( -ve). We saw in the previous tutorial, that the gate of a junction field effect transistor, JFET must be biased in such a way as to reverse-bias the pn-junction. The gate electrode is placed on top of a very thin insulating layer and there are a pair of small n-type regions just under the drain and source electrodes. Both the Depletion and Enhancement type MOSFETs use an electrical field produced by a gate voltage to alter the flow of charge carriers, electrons for n-channel or holes for P-channel, through the semiconductive drain-source channel. The construction of the Metal Oxide Semiconductor FET is very different to that of the Junction FET. The direction of the arrow pointing to this channel line indicates whether the conductive channel is a P-type or an N-type semiconductor device. If the channel line is shown as a dotted or broken line, then it represents an “Enhancement” (normally-OFF) type MOSFET as zero drain current flows with zero gate potential. If this channel line is a solid unbroken line then it represents a “Depletion” (normally-ON) type MOSFET as drain current can flow with zero gate biasing potential. The line in the MOSFET symbol between the drain (D) and source (S) connections represents the transistors semiconductive channel. When this is the case, as in enhancement types it is omitted from the symbol for clarification. Usually in discrete type MOSFETs, this substrate lead is connected internally to the source terminal. It connects to the main semiconductive channel through a diode junction to the body or metal tab of the MOSFET. The four MOSFET symbols above show an additional terminal called the Substrate and is not normally used as either an input or an output connection but instead it is used for grounding the substrate. 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.