JFET

The junction field-effect transistor (JFET) is one of the simplest types of <a href="/facts/Field-effect_transistor/TerYC6Nz">field-effect transistor</a>. JFETs are three-terminal <a href="/facts/Semiconductor/zFf3mGTE">semiconductor</a> devices that can be used as <a href="/facts/Electronics/E4JhgISq">electronically</a> controlled <a href="/facts/Switch/vqbNDgYm">switches</a> or <a href="/facts/Voltage-controlled_resistor/GzHQqKUu">resistors</a>, or to build <a href="/facts/Amplifier/pnRgxncC">amplifiers</a>. 
Unlike <a href="/facts/Bipolar_junction_transistors/9BMcGv5Q">bipolar junction transistors</a>, JFETs are exclusively <a href="/facts/Voltage/EN2po6N2">voltage</a>-controlled in that they do not need a <a href="/facts/Biasing/lK0e6hbK">biasing current</a>. <a href="/facts/Electric_charge/xxsBfmlB">Electric charge</a> flows through a <a href="/facts/Semiconducting/zFf3mGTE">semiconducting</a> channel between source and drain <a href="/facts/Terminal_(electronics)/CwbKGSuB">terminals</a>. By applying a reverse bias <a href="/facts/Voltage/EN2po6N2">voltage</a> to a gate terminal, the channel is <a href="/facts/Channel_length_modulation/X0LJ5039">pinched</a>, so that the <a href="/facts/Electric_current/Dc1xdnUX">electric current</a> is impeded or switched off completely. A JFET is usually conducting when there is zero voltage between its gate and source terminals. If a potential difference of the proper <a href="/facts/Electrical_polarity/fGRB4SGP">polarity</a> is applied between its gate and source terminals, the JFET will be more <a href="/facts/Resistive/hxSt0UAj">resistive</a> to current flow, which means less current would flow in the channel between the source and drain terminals.
JFETs are sometimes referred to as <a href="/facts/Depletion-mode/KB0o8lya">depletion-mode</a> devices, as they rely on the principle of a <a href="/facts/Depletion_region/54fB1pfE">depletion region</a>, which is devoid of majority <a href="/facts/Charge_carrier/wpjjql4x">charge carriers</a>. The depletion region has to be closed to enable current to flow.
JFETs can have an <a href="/facts/N-type_semiconductor/d9GPL5tV">n-type</a> or <a href="/facts/P-type_semiconductor/d9GPL5tV">p-type</a> channel. In the n-type, if the voltage applied to the gate is negative with respect to the source, the current will be reduced (similarly in the p-type, if the voltage applied to the gate is positive with respect to the source). Because a JFET in a <a href="/facts/Common_source/8UDNcIpv">common source</a> or <a href="/facts/Common_drain/fJRvThwB">common drain</a> configuration has a large <a href="/facts/Input_impedance/AQCLaTj9">input impedance</a> (sometimes on the order of 1010 <a href="/facts/Ohm/QNVrlGjw">ohms</a>), little current is drawn from circuits used as input to the gate.

JFET open-in-new

JFET