When base current is increased up to its limitation collector current also increase up to its last value. This we can say that the transistor now falls into the active region.
When the base current Ib increases collector current Ic also increases. This region we can call as a cut-off region where Ib = 0 so that Ic is also zero. So, that there is no current flow in the transistor circuit. In common collector circuit, if the input current is zero then output current is also zero. After that, we repeat this process for higher different constant base voltage ( Ib = 20 μA, 40μA, 60μA, 80μA, 100μA ). Here first we take a reading of Ie and Vec at a constant base current Ib =0 μA. You can see output characteristics in the above figure. By taking constant Ib we increase Vec and note down emitter current ( Ie ). To determine output characteristics, we kept base current Ib constant and take readings. Emitter-collector voltage is shown on the X-axis. Here emitter current Ie is shown on Y-axis. Output characteristics is a curve between output current ( here emitter current Ie) and output voltage ( emitter-collector voltage Vec ) at a constant base current Ib. After that we take Vec= 5 V and take reading as same in previous reading.
You can see the input characteristics of CC below.įirst here we take reading of base current (Ib) and base-collector voltage (Vbc) on constant Vec = 3 V. Base-current voltage Vcb is shown in X-axis. Input characteristics of common collector circuit is a curve between input current ( here base current = Ib ) and input voltage ( here base-collector voltage= Vcb ) at constant emitter-collector voltage ( Vec). This circuit provides same current gain as common emitter circuit. The current amplification factor is the ratio of change in emitter current ( Ie) to change in base current ( Ib ).Ĭurrent amplification factor (γ) = ΔIe / ΔIb Here for common collector circuit, the input current is base current ( IB) and output current is emitter current ( Ie). The current amplification factor is the ratio of change in output current to change in input current. Figure 1 shows a CC connection of PNP transistor and Figure 2 shows CC connection of NPN transistor.īy the common collector, we can find the current amplification factor. Below figure shows the common collector circuit for the transistor. You can note here for both input and output side collector terminal is common terminal. In this type of arrangement, an input is applied between base and collector and output is taken between emitter and collector terminals. It mostly used for an impedance matching application due to their high input resistance. In our most practical life generally common emitter type transistor used mostly but in some applications this type of transistor also used. Because of that, it called a common collector( CC) transistor. In this type of configuration collector is common terminal between other both emitter and base terminals. Common collector configuration of the Transistor :. We already cover CE and CB configuration in a previous article here we take a detailed article on CC configuration of the transistor. Amplifier circuit can be designed by any of this type of configurations but every configuration have some advantages and applications. Common emitter connection, common base connection, and common collector. You could try to swap them, but you'll get a very low \$H_\$, probably even less than 1.Here we cover topics – common collector configuration of the transistor – circuits, characteristics, applications, disadvantage, why it is called emitter-follower circuit?Īs we see in the previous article, there is basically three type of transistors connections. The emitter is heavily doped, while the collector is lightly doped. The main differences between emitter and collector are doping concentration and size. But conventional flow can't explain the details of the working of a transistor, so here electron flow is shown.Īlso note that the collector voltage is higher than the base voltage. Conventional flow is from positive to negative and is always used in circuit analysis. The arrows indicate electron flow, not conventional flow. When you use an NPN transistor as a transistor, current will from collector to emitter through the base, even though the base-collector junction reverse biased.
Since the junctions act like diodes they don't conduct in both directions if you apply a voltage across the two pins. Yes, BJTs have the same voltage drop across their junctions as common diodes, that's 0.6V to 0.7V between base and emitter, and the same between base and collector.