Cutoff

In the operating region of a transistor, when the collector-emitter voltage is below the threshold value, it is canceled by reverse bias, resulting in no base current flow. In the cutoff state, the graph showing the relationship between the collector current and collector-emitter voltage of a transistor represents the saturation region. Therefore, to avoid cutoff, it is common to use the transistor with a collector-emitter voltage above the threshold value.

In a switching power supply circuit, in a choke-input type rectifier circuit used for harmonic current suppression, when the load varies greatly, a situation occurs where the main switching element is in the off state, causing large fluctuations in the rectified output current. At this time, cutoff also refers to the state where the current in the reactor becomes discontinuous and does not flow due to the main switching element being off.