Definition
In a junction field-effect transistor (JFET), the gate-to-source voltage at which the channel between the source and drain becomes so narrow that current flow through the transistor is reduced to a very small cutoff value. Beyond this voltage, the transistor is effectively switched off.
Plain English
The voltage applied to a certain type of transistor that 'pinches' its internal channel shut, stopping current from flowing through it.
Context Anchor
Seen in aircraft electronics, avionics, voltage regulators, and maintenance troubleshooting involving transistor circuits.
Derivation
From 'pinch off,' meaning to squeeze something closed. The term describes what happens physically inside the transistor: the conducting channel narrows under the influence of the gate voltage until it is effectively pinched shut, blocking current flow.
Why Pilots Care
A pilot usually does not calculate pinch-off voltage in flight, but maintenance personnel use it when checking or replacing electronic components. If a transistor does not turn off at the correct voltage, an aircraft electronic circuit may not control power or signals correctly.
Analogy
Like squeezing a garden hose tighter and tighter until no water can get through. The pinch-off voltage is the point at which the squeeze is just enough to stop the flow.
Grounding Statement
When the control voltage reaches the pinch-off voltage, the transistor’s current path is effectively shut off.
Intuition Check
Pinch-off does not mean a wire is physically squeezed or broken. It means an electrical control voltage has stopped current flow inside the transistor.
Example Sentence 1
The technician measured the pinch-off voltage of the JFET to confirm it matched the manufacturer's specification before installing it in the radio.
Example Sentence 2
When the gate voltage reached pinch-off voltage, current stopped flowing through the transistor circuit.