cutoff

In the operating region of a transistor, when the collector-emitter voltage falls below the threshold value, the reverse bias cancels it out, causing no base current to flow. In the cutoff state, the graph showing the relationship between the collector current and collector-emitter voltage of the transistor shifts to the saturation region. Therefore, to avoid cutoff, the collector-emitter voltage is usually kept above the threshold value.

In switching power supply circuits, in choke input type rectifier circuits used for suppressing harmonic currents, when the load changes significantly, a state in which the main switching element is turned off occurs, leading to large fluctuations in rectified output current. At this time, due to the off state of the main switching element, the current in the reactor becomes discontinuous and does not flow — this state is also referred to as cutoff.