In electronics, cut-off is a state of negligible conduction 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 n ...

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 t ...

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 movin ...

, 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 t ...

), 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 A device is usually a constructed tool. Device may also refer to: Technology Computing * Device, a colloquial term encompassing desktops, laptops, tablets, smartphones, etc. * Device file, an interface of a device driver * Peripheral, any devi ...

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 quantity ...

of this transition varies considerably.

Cutoff values

Diodes

Copper oxide diode Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-or ...

: 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 voltag ...

:0.10–0.45, varying with temperature. *

Selenium diode Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium ...

:Depends on age and current. Usually higher than silicon diodes. * Silicon 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 var ...

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

Transistors

* BJT: Depends on the configuration. *

Germanium transistor Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbors s ...

: 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 trad ...

: 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). ...

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 1 ...

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 co ...

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 reciproc ...

, 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. 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 The EF86 is a high transconductance sharp cutoff pentode vacuum tube with Noval (B9A) base for audio-frequency applications. It was introduced by the Mullard company in 1953 and was produced by Philips, Mullard, Telefunken, Valvo, and GEC amon ...

and

6AK5 The 6AK5 vacuum tube is a miniature 7-pin sharp-cutoff pentode used as RF or IF amplifier especially in high-frequency wide-band applications at frequencies up to 400 MHz. It was developed by Bell Labs / Western Electric and used extensively as ...

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