12/16/2023 0 Comments Pnp transistor definition![]() ![]() The base region is very lightly doped and is a p-type semiconductor, therefore has a few holes as the charge carriers. In an n-type semiconductor the majority charge carriers are the electrons and thus, start moving towards the base junction, thus the name emitter current, I E. ![]() Please note that the depletion region behaves as the opposition to the flow of current, therefore, the thinner the layer the more the current flow in that region. The depletion region of the emitter-base region is smaller as compared to the collector-base region. Similarly, for the collector-base region, the positive supply of V CC is connected to the n-type semiconductor and thus made reverse biased. Now we must understand here how to make a junction forward or reverse biased?Īs the n-type of semiconductor comes first when talking about the emitter-base region therefore, the negative of the voltage supply gets connected with it to make it in forward bias. Also, the collector-base junction is reverse biased and V EE is the supply for this region. ![]() The emitter region is always connected to the negative supply and the collector with the positive one.Īs shown in the fig, the base-emitter junction is made forward biased with a supply voltage as V CC. Here, the base region has the control for ON/OFF of the transistor based on the input given to it. The emitter is moderately doped with the least doping in the base region (lightly doped p-semiconductor). ![]() The common-collector circuit can be shown mathematically to have a voltage gain of almost unity:Ī v = v out v in ≈ 1.The three terminals emitter, base, and collector are all doped differently. It never saturates even if the input voltage reaches the positive rail. It depends slightly on various disturbances (transistor tolerances, temperature variations, load resistance, a collector resistor if it is added, etc.), since the transistor reacts to these disturbances and restores the equilibrium. Intuitively, this behavior can be also understood by realizing that V BE is very insensitive to bias changes, so any change in base voltage is transmitted (to good approximation) directly to the emitter. As a result, the output voltage follows the input voltage variations from V BE up to V + hence the name "emitter follower". The transistor continuously monitors V diff and adjusts its emitter voltage to equal V in minus the mostly constant V BE by passing the collector current through the emitter resistor R E. Thus the two voltages are subtracted according to Kirchhoff's voltage law (KVL) (the subtractor from the function block diagram is implemented just by the input loop), and their difference V diff = V in − V out is applied to the base–emitter junction. 2 with β = 1), the entire output voltage V out is placed contrary and in series with the input voltage V in. 1) is an amplifier with full series negative feedback. From this viewpoint, a common-collector stage (Fig. The circuit can be explained by viewing the transistor as being under the control of negative feedback. The analogous field-effect transistor circuit is the common drain amplifier and the analogous tube circuit is the cathode follower.īasic circuit Figure 2: A negative-feedback amplifier In this circuit the base terminal of the transistor serves as the input, the emitter is the output, and the collector is common to both (for example, it may be tied to ground reference or a power supply rail), hence its name. In electronics, a common collector amplifier (also known as an emitter follower) is one of three basic single-stage bipolar junction transistor (BJT) amplifier topologies, typically used as a voltage buffer. ( April 2009) ( template removal help)įigure 1: Basic NPN common collector circuit (neglecting biasing details). Please help to improve this article by introducing more precise citations. This article includes a list of general references, but it lacks sufficient corresponding inline citations. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |