![]() Devices working on the principle of one current controlling another current are known as current-controlled devices. Devices utilizing a voltage as the controlling signal are, not surprisingly, called voltage-controlled devices. ![]() One type of active device uses a voltage to control the current while another type of active devices uses another current to be the controlling signal. All active devices control the flow of current through them. For a circuit to be called electronic, it must contain at least one active device. Where I C = collector current, I E = emitter current, and I B = base current.An active device is any type of component with the ability to electrically control the flow of current (controlling one electric signal with another electric signal). The transistor operates in cutoff region when both the emitter and collector junctions are reverse biased.Īs in cutoff region, the collector current, emitter current and base currents are nil, we can write as The figure below shows a transistor working in cutoff region. The collector, emitter and base currents are all zero in this mode of operation. The transistor has the effect of its collector and base being opened. This is the region in which transistor tends to behave as an open switch. Where I C = collector current and I E = emitter current. The transistor operates in saturation region when both the emitter and collector junctions are forward biased.Īs in the saturation region the transistor tends to behave as a closed switch, The following figure shows a transistor working in saturation region. The collector and emitter currents are maximum in this mode of operation. The transistor has the effect of its collector and emitter being shorted. This is the region in which transistor tends to behave as a closed switch. Where I C = collector current, β = current amplification factor, and I B = base current. ![]() In the active state, collector current is β times the base current, i.e. The transistor operates in active region when the emitter junction is forward biased and collector junction is reverse biased. This region lies between saturation and cutoff. The following circuit diagram shows a transistor working in active region. A transistor while in this region, acts better as an Amplifier. This is the region in which transistors have many applications. Emitter JunctionĪmong these regions, Inverse active region, which is just the inverse of active region, is not suitable for any applications and hence not used. This is understood by having a look at the following table. These biasing methods make the transistor circuit to work in four kinds of regions such as Active region, Saturation region, Cutoff region and Inverse active region (seldom used). Either forward or reverse biasing is done to the emitter and collector junctions of the transistor. The supply of suitable external dc voltage is called as biasing. Reverse biased is the condition where a positive voltage is applied to the n-type and negative voltage is applied to the p-type material. Forward biased is the condition where a positive voltage is applied to the p-type and negative voltage is applied to the n-type material. The junctions are forward biased and reverse biased based on our requirement. This DC supply is given to the two PN junctions of a transistor which influences the actions of majority carriers in these emitter and collector junctions. The DC supply is provided for the operation of a transistor. Emitter Follower & Darlington Amplifier.Transformer Coupled Class A Power Amplifier.
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