BJT Cutoff region

This article is centre at Bipolar Junction Transistor (BJT) cutoff region or FULLY OFF region.


In Bipolar Junction Transistor (BJT) cut off region or fully off region, the transistor is bias in such a way that both junctions are reverse so that no current will pass from the emitter (E) to the collector (C). In this mode, the transistor is in OFF mode.

When we study the below circuits, two PN-junction diodes are configure to form two types of layers. These are NPN layers and PNP layers. In NPN layers; P-dope is the common junction while in PNP layers; N-dope is the common junction. Both the configurations are in reverse modes. By connecting the base (B) to the emitter (E) that is to say; the base (B) is lower than the collector (C); current will not flow from the emitter (E) to the collector (C). This is because the PN-Junction, from the base (B) to the collector is in reverse direction, at this state the transistor is “fully OFF.” Note that PNP emitter terminal is always connected to the positive potential difference while its collector to the ground or 0v.

NPN PN junction cutoff

    PNP PN junction cutoff


The below circuits explain and illustrate the operations of the cut OFF regions or fully OFF regions for both the NPN bipolar junction transistor (BJT) and PNP bipolar junction transistor (BJT). The resistor R in the circuits limits the current that will pass through the Light Emitting Diode (LED).




Apart from Bipolar Junction Transistor (BJT) cutoff region or FULLY OFF region, you might read also the other two operation regions below:


A transistor is said to be saturated (Fully ON) when it is biased in such a way that current passes from the Emitter (E)  to the Collector (C). In NPN and PNP bipolar junction transistors (BJTs), connecting the base (B) to the collector (C) makes the…..Read more> BJT Saturation Region


In active region the transistor is bias so that the base (B) measures a higher potential difference (Pd) to the emitter (E) but lower than the collector (C) to the emitter (E). In this region the transistor is always active. This is the biasing mode or region…..Read more> BJT Active Region


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