In electronics, cut-off is a state of negligible

conduction Conductor or conduction may refer to: Music * Conductor (music), a person who leads a musical ensemble, such as an orchestra. * Conductor (album), ''Conductor'' (album), an album by indie rock band The Comas * Conduction, a type of structured f ...

that is a property of several types of

electronic component An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not ...

s when a control parameter (that usually is a well-defined

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...

electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...

, but could also be an incident light intensity or a

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

), is lowered or increased past a value (the conduction threshold). The transition from normal conduction to cut-off can be more or less sharp, depending on the type of device considered, and also the

speed In everyday use and in kinematics, the speed (commonly referred to as ''v'') of an object is the magnitude of the change of its position over time or the magnitude of the change of its position per unit of time; it is thus a scalar quanti ...

of this transition varies considerably.

Cutoff values

Diodes

* Copper oxide diode: Usually between germanium and silicon diodes (0.2-0.5V) * Diac: Depends on configuration. *

Germanium diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode ...

:apx 0.3 V; varying with temperature. *

Schottky diode The Schottky diode (named after the German physicist Walter H. Schottky), also known as Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltage ...

:0.10–0.45, varying with temperature. * Selenium diode:Depends on age and current. Usually higher than silicon diodes. *

Silicon diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode ...

: cutoff occurs when Vf falls below apx 0.7 V. The exact voltage varies with temperature. *

Thermionic diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode ...

: cutoff voltage depends on device design. Much higher than for silicon devices. *

Zener diode A Zener diode is a special type of diode designed to reliably allow current to flow "backwards" (inverted polarity) when a certain set reverse voltage, known as the ''Zener voltage'', is reached. Zener diodes are manufactured with a great varie ...

: reverse cutoff defined by diode voltage rating. Forward cutoff apx 0.6 V.

Transistors

BJT A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipolar ...

: Depends on the configuration. * Germanium transistor: apx 0.2 V, varying with temperature. *

MOSFET The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...

: Depends on the configuration. *

Silicon transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...

: apx 0.6 V, varying with temperature. *

TRIAC A TRIAC (triode for alternating current; also bidirectional triode thyristor or bilateral triode thyristor) is a three terminal electronic component that conducts current in either direction when triggered. The term TRIAC is a genericised tradem ...

: Also depends on the configuration.

Valves

Triodes A triode is an electronic amplifying vacuum tube (or ''valve'' in British English) consisting of three electrodes inside an evacuated glass envelope: a heated filament or cathode, a grid, and a plate (anode). Developed from Lee De Forest's 190 ...

: triodes cut off when applied grid bias is too low. This will be a negative voltage under ordinary conditions. *

Tetrode A tetrode is a vacuum tube (called ''valve'' in British English) having four active electrodes. The four electrodes in order from the centre are: a thermionic cathode, first and second grids and a plate (called ''anode'' in British English). Th ...

pentode A pentode is an electronic device having five electrodes. The term most commonly applies to a three-grid amplifying vacuum tube or thermionic valve that was invented by Gilles Holst and Bernhard D.H. Tellegen in 1926. The pentode (called a ''tripl ...

etc.: There is some degree of interaction between the grids, and values will vary from one device to another. Anode voltage also affects cutoff voltage. Prolonged periods in cut-off leads to ''cathode poisoning''.

Remote cutoff

vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...

(such as a

, but also sometimes

triode A triode is an electronic amplifying vacuum tube (or ''valve'' in British English) consisting of three electrodes inside an evacuated glass envelope: a heated filament or cathode, a grid, and a plate (anode). Developed from Lee De Forest's 19 ...

s, hexodes, heptodes and so on) with its

control grid The control grid is an electrode used in amplifying thermionic valves (vacuum tubes) such as the triode, tetrode and pentode, used to control the flow of electrons from the cathode to the anode (plate) electrode. The control grid usually consists ...

given a helix with a variable pitch can be made to operate with more negative grid voltages, with reduced amplification, before it is completely cut off (i.e. yielding no significant output). This ability to vary the amplification (sometimes called mu) and also the

transconductance Transconductance (for transfer conductance), also infrequently called mutual conductance, is the electrical characteristic relating the current through the output of a device to the voltage across the input of a device. Conductance is the reciproca ...

, is useful in

Automatic Gain Control Automatic gain control (AGC) is a closed-loop feedback regulating circuit in an amplifier or chain of amplifiers, the purpose of which is to maintain a suitable signal amplitude at its output, despite variation of the signal amplitude at the inpu ...

(AGC) stages of

radio receivers In radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. The ...

. Devices with this characteristic are called remote-cutoff or variable-mu or super-control types.

Sharp cutoff

With a normal

arrangement, a

will have close to a square-law relationship between input (grid) voltage and output (anode/plate) current, with the latter falling sharply to roughly zero. This characteristic is normally required for linear RF and audio uses. Examples; EF86 and 6AK5.

Semi-remote cutoff

A semi-remote cutoff device has characteristics somewhere between a remote-cutoff device and a sharp-cutoff one.

References

External links

Explanation of sharp-cutoff control grids in vacuum tubes.

Electrical parameters {{Electronics-stub