BJT active region

In this post, you will learn about bipolar junction transistor (BJT) active region. Also after this, links for the other two operation regions are provided immediately.


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 which transistor amplifiers use for their operations.

The below circuits explain and illustrate the operations of the Active regions for both 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).


NPN bjt active region

PNP bjt acting region


Apart from the BJT active region, below are links to the other two operation region of bipolar junction transistor (BJT). That is; cut off (FULLY OFF) region and saturation (FULLY ON) 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)…READ THIS


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 PN-junction from the base (B) to the emitter (E) to be forward bias. As a result of this, the base (B) to the collector (C) of the…READ THIS


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