normallyoff

Normally-off refers to a device or circuit that presents a non-conductive or inactive state by default, requiring a specific input or action to become conductive or active. In the resting condition, there is little to no current flow between the device’s terminals; applying the designated control signal changes the state to on or active. The concept is widely used across electronics, electrical engineering, and control systems to emphasize a safe, nonconducting baseline.

In transistors, normally-off behavior is typical of enhancement-mode devices. An enhancement-mode MOSFET, for example, remains off when the gate-to-source voltage is zero; a sufficient gate voltage (positive for NMOS, negative for some PMOS configurations) creates a conductive channel. Depletion-mode devices, by contrast, are often described as normally-on, since they conduct at zero gate voltage.

In switching and relay technology, normally-off or normally-open configurations describe states where the circuit is open in the absence of a control signal. A relay contact that is normally open does not connect the circuit until the relay is energized. This default-off characteristic is valued for safety and failsafe design, ensuring that loss of control returns the system to a non-conductive state.

Design considerations for normally-off devices include leakage currents in the off state, switching thresholds, and reliability of the control signal. Applications span power electronics, digital logic, relays, and safety-critical systems where a conservative default state is desirable. See also normally-open and normally-closed concepts in switch terminology.