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 electronic device or physical entity part of an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singula ...
s when a control parameter (that usually is a well-defined
voltage
Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...
or
electric current
An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...
, but could also be an incident
light intensity or a
magnetic field
A magnetic field (sometimes called B-field) is a physical 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 ...
), 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 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 non-negative scalar quantity. Intro ...
of this transition varies considerably.
Cutoff values
Diodes
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Copper oxide diode: Usually between germanium and silicon diodes (0.2-0.5V)
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Diac: Depends on configuration.
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Germanium diode:apx 0.3 V; varying with temperature.
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Schottky diode:0.10–0.45, varying with temperature.
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Selenium diode:Depends on age and current. Usually higher than silicon diodes.
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Silicon diode: cutoff occurs when Vf falls below apx 0.7 V. The exact voltage varies with temperature.
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Thermionic diode: cutoff voltage depends on device design. Much higher than for silicon devices.
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Zener diode: reverse cutoff defined by diode voltage rating. Forward cutoff apx 0.6 V.
Transistors
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BJT: Depends on the configuration.
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Germanium transistor: apx 0.2 V, varying with temperature.
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MOSFET
upright=1.3, Two power MOSFETs in amperes">A in the ''on'' state, dissipating up to about 100 watt">W and controlling a load of over 2000 W. A matchstick is pictured for scale.
In electronics, the metal–oxide–semiconductor field- ...
: Depends on the configuration.
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Silicon transistor: apx 0.6 V, varying with temperature.
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TRIAC: Also depends on the configuration.
Valves
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Triodes: triodes cut off when applied grid bias is too low. This will be a negative voltage under ordinary conditions.
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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 electrode, plate (called ''anode'' in Bri ...
,
pentode 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
A
vacuum tube
A vacuum tube, electron tube, thermionic 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. It ...
(such as a
pentode, but also sometimes
triode
A triode is an electronic amplifier, amplifying vacuum tube (or ''thermionic valve'' in British English) consisting of three electrodes inside an evacuated glass envelope: a heated Electrical filament, filament or cathode, a control grid, grid ...
s,
hexodes, heptodes and so on) with its
control grid 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, is useful in
Automatic Gain Control (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
control grid arrangement, a
vacuum tube
A vacuum tube, electron tube, thermionic 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. It ...
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.
See also
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Diode
A diode is a two-Terminal (electronics), terminal electronic component that conducts electric current primarily in One-way traffic, one direction (asymmetric electrical conductance, conductance). It has low (ideally zero) Electrical resistance ...
*
Electrical conduction
*
Electronic component
An electronic component is any basic discrete electronic device or physical entity part of an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singula ...
*
Field effect transistor
The field-effect transistor (FET) is a type of transistor that uses an electric field to control the current through a semiconductor. It comes in two types: junction FET (JFET) and metal-oxide-semiconductor FET (MOSFET). FETs have three termi ...
in
JFET and
MOSFET
upright=1.3, Two power MOSFETs in amperes">A in the ''on'' state, dissipating up to about 100 watt">W and controlling a load of over 2000 W. A matchstick is pictured for scale.
In electronics, the metal–oxide–semiconductor field- ...
form
*
Transistor
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
*
Vacuum tube
A vacuum tube, electron tube, thermionic 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. It ...
References
External links
Explanation of sharp-cutoff control grids in vacuum tubes.
Electrical parameters
{{Electronics-stub