9.3.2. Voltage and Current Calculations

So, we will be going little more detail with this kind of circuit. In fact, we will be varying this voltage and then we will see that what kind of variation or effect it is coming to the collector side that detail when we will be dealing with the amplifier.

Now, so far we are considering about the n-p-n transistor if you look into the p-n-p transistor on the other hand it is very similar, but of course, it is the 3 islands or 3 regions are different. Namely, we do have p-region and then n-region and then p-region, so we do have p-n-p.

In this section, we start with an introduction to N-P-N and P-N-P transistors. Both are types of bipolar junction transistors (BJTs) that consist of three regions: for N-P-N, the regions are N, P, and N; for P-N-P, the regions are P, N, and P. Understanding the orientation of these regions is crucial because it determines how the transistor will operate based on the biasing.

Think of transistors like traffic controllers. Just as they manage the flow of vehicles (current) at intersections (junctions), transistors control the flow of electrical current in circuits based on the type of junctions (N or P type) they have.

And here also to keep the device in an active region of operation base and emitter junction need to be a forward bias which means that at the emitter now we are looking for higher voltage with respect to the base. On the other hand, the other junction the base to collector junction we like to keep it is in reverse bias, namely the base should be at higher potential with respect to the collector.

For the transistor to operate correctly, it must be biased properly. In an N-P-N transistor, the base-emitter junction must be forward-biased, meaning the emitter must have a higher voltage than the base. Conversely, the base-collector junction must be reverse-biased, meaning the base needs to be at a higher potential than the collector. This ensures that the transistor remains in its active region, allowing it to amplify signals.

Consider a water valve: if you want water (electric current) to flow from a higher tank (emitter) to a lower one (collector), the valve (transistor) has to be positioned correctly (biased) to control that flow. Adjusting the heights (voltages) ensures that you can control how much water goes through.

In other words, the emitter current entering to the device and the base current it is emerging out of the base and the collector current also it is emerging out of the collector. So, that is the axial direction of the currents. So, you may say that this is the actual polarity a positive direction of the current and. So, we do have I_E, we do have I_B and then we do have I_C like this.

There are three types of currents to consider in a transistor: emitter current (I_E), base current (I_B), and collector current (I_C). The emitter current is the current flowing into the device, while the base current flows out of the base terminal, and the collector current flows out of the collector. These currents must be understood in terms of their direction and how they relate to each other, as the collector current is typically a multiple of the base current (dictated by the transistor's current gain, β).

Think of a transistor as a funnel: the emitter is where you pour the liquid (I_E), the base is where some of it flows out (I_B), and the rest flows into the collector (I_C). The way you pour affects how much comes out at each point.

So, if you compare the notation or seem the equation we have used for BJT this n-p-n BJT with p-n-p what you can see here it is. So, these are the equations it was used for n-p-n. So, with respect to that we simply have to modify this part namely we can make it V_EB. So, likewise here we can replace this is V_EB and this is into V_EC.

The equations used for both N-P-N and P-N-P transistors are fundamentally similar but require changing how voltages are denoted based on polarity changes. For example, V_EB represents the voltage between the emitter and base, while V_EC represents the voltage between the emitter and collector. Understanding these notations helps in correctly applying the formulas for analysis.

Imagine changing road signs when you cross a border into another country—while the concepts of navigation remain the same, the symbols and directions might change. In transistors, we do the same with voltages and currents when switching between N-P-N and P-N-P to keep everything clear.

Now, you may recall whatever the graphical interpretation we do have or representation of the I-V characteristic of say I_B as function of V_EB. So, if you plot this characteristic of course, it will be exponential in this like as you have discussed before.

The I-V characteristics for transistors reflect how the current varies with voltage. For a P-N-P transistor, the characteristics will also show exponential behavior, similar to N-P-N transistors but plotted using the adjusted voltage notations. By understanding these plots, we can predict and analyze the behavior of transistors under various conditions.

Think of these graphs like a temperature scale for a weather report. Different readings (voltages) yield different conditions (currents). Just as you can predict if it’ll be a sunny or rainy day based on the temperature, we can predict the behavior of the transistor by analyzing its I-V characteristics.

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