Cut-off (electronics)

In electronics, the term Cut-off identifies a state of negligible electrical conduction which is proper of several types of electronic components when a control parameter (which usually is a well-defined voltage or electric current, but could also be an incident light intensity or a magnetic field), is lowered or increased past a value called conduction threshold or simply 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 of this transition varies considerably.

Cutoff values

Diodes

• Silicon diode: cutoff occurs when Vf falls below apx 0.6 V. The exact voltage varies with temperature.
• Germanium diode: apx 0.3 V, varying with temperature
• Schottky diode:
• Diac:
• Zener diode: reverse cutoff defined by diode voltage rating. Forward cutoff apx 0.6 V.
• Thermionic diode: cutoff voltage depends on device design. Much higher than for silicon devices.
• Copper oxide diode:
• Selenium diode:

Transistors

• Silicon transistor: apx 0.6 V, varying with temperature.
• Germanium transistor: apx 0.2 V, varying with temperature
• BJT:

• MOSFET:
• Triac:

Valves

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

See also

• Diode
• Electrical conduction
• Electronic component
• Field effect transistor in JFET and MOSFET form
• Transistor
• Vacuum tube

External links

• Explanation of remote-cutoff control grids in vacuum tubes.
• Explanation of sharp-cutoff control grids in vacuum tubes.