gate off
To turn something off by controlling its gate.
gate off: kill a circuit by blocking its control electrode
To gate off is to interrupt current flow through a semiconductor device by applying a blocking voltage to its gate terminal. In power electronics, this means stopping conduction through a transistor, thyristor, or other gated device by removing or reversing the gate signal. The gate is the control electrode whose voltage determines whether the device conducts or blocks, so gating it off closes the switch without mechanical contact.
The term applies across several device families. MOSFETs are gated off by reducing gate voltage below the threshold voltage, typically 2 to 5 volts for logic-level devices, or 10 to 15 volts for power MOSFETs. IGBTs are gated off similarly, though they hold charge in the base region that must dissipate, creating a tail current during turn-off. Thyristors and SCRs are more complex: they cannot be gated off once fired; they must be turned off by reducing anode current below the holding current, or by applying a reverse voltage through a commutation circuit.
Switching speed and circuit design
How quickly a device gates off matters enormously. A MOSFET can gate off in nanoseconds because charge leaves the gate capacitance quickly, but the actual current fall depends on parasitic inductance in the circuit loop. An IGBT turns off more slowly, often in hundreds of nanoseconds, because trapped charge in the base takes time to recombine. Fast gating off reduces switching losses and heat dissipation, but generates electromagnetic noise that must be filtered with snubber circuits or gate resistors.
In motor drives and power supplies, gating off one device in a switching pair (like a half-bridge) while gating on the other allows PWM control of output voltage and current. Dead time, a period when both devices are off, prevents shoot-through where both conduct simultaneously and short the supply. Protection circuits must gate off fast enough to prevent damage if a fault is detected, such as overcurrent or overvoltage, so the gate driver itself is a critical design element.
The language reflects the control mechanism: you gate off an electronic device the way you might gate off a physical passage. The gate controls access. Unlike mechanical switches which are simply open or closed, gated devices exist in a spectrum from off through partially conducting to fully on, depending on gate voltage, making them essential for analog control and switching power conversion.