{"id":2309,"date":"2024-01-23T17:51:42","date_gmt":"2024-01-23T17:51:42","guid":{"rendered":"https:\/\/partstack.com\/blog\/?p=2309"},"modified":"2024-01-25T14:18:08","modified_gmt":"2024-01-25T14:18:08","slug":"npn-vs-pnp-transistors-differences-applications","status":"publish","type":"post","link":"https:\/\/partstack.com\/blog\/npn-vs-pnp-transistors-differences-applications\/","title":{"rendered":"NPN vs. PNP Transistors: Exploring the Working Differences and Key Distinctions"},"content":{"rendered":"

The Fundamental Role of Transistors in Modern Electronics<\/h2>\n

Transistors are electronic devices that are building blocks of ICs, both analog and digital. These are among the most commonly used electronic components. That’s why almost all novel technologies use transistors in one way or another. These technologies range from bullet trains to remote control. Transistors have three terminals, and they are doped semiconductor devices. Transistors perform two main functions: switching and amplification.<\/p>\n

\"Transistor\"<\/p>\n

Figure 1: Transistor<\/p>\n

There are two major families of transistors: FETs<\/a> and BJTs<\/a>. The transistors can be either bipolar or unipolar. The charge carriers for bipolar transistors are electrons and holes. BJTs are examples of bipolar transistors. The charge carriers for unipolar transistors can be either electrons (in the case of n-channel) or holes (in the case of p-channel). MOSFETs<\/a> and JFETs are examples of unipolar transistors.<\/p>\n

The two major configurations for transistors are PNP and NPN. The PNP refers to positive\u2013negative\u2013positive. It has two layers of positive semiconductors and one layer of negative semiconductors. The NPN refers to negative-positive-negative. It has two layers of negative semiconductors and one layer of positive semiconductors.<\/p>\n

Terminals and Doping Characteristics of a Transistor<\/h3>\n

There are three terminals within a transistor, as Figure 1 indicates. The base(B), the emitter(E), and the collector(C). Normally, the base is lightly doped and has a small width. The emitter is heavily doped and is of normal width. The collector is moderately doped and is larger in width than both the base and the emitter. These are shown in the figure 2.<\/p>\n

\"Terminals<\/p>\n

Figure 2: Terminals within transistor<\/p>\n

Working of NPN Transistor<\/h2>\n

NPN Transistor Configuration<\/h4>\n

In an NPN transistor, the collector and the emitter are doped with an n-type impurity, whereas the base is doped with a p-type impurity. This is shown in the figure below:<\/p>\n

\"npn<\/p>\n

Figure 3: NPN Transistor Configuration<\/p>\n

The positive voltage is applied to the collector, and the direction of conventional current is from the collector to the emitter. The majority of charge carriers in n-type regions, i.e., emitter and collector, are electrons, and minority charge carriers are holes. The majority charge carriers in p-type regions, i.e., base are holes, and electrons are minority charge carriers. Hence, the majority of charge carriers in an NPN transistor are electrons.<\/p>\n

NPN Transistor Symbol<\/h4>\n

The symbol for an NPN transistor is shown below:<\/p>\n

\"npn<\/p>\n

Figure 4: Symbol for an NPN Transistor<\/p>\n

Circuit Diagram for NPN Transistor<\/h4>\n

In the NPN transistor, two pn junctions are formed; one is the emitter-base junction, and the other is a collector-base junction. The transistor works in active mode, so the base-emitter junction is forward-biased, and the collector-base junction is reverse-biased through supply voltage. The collector and the emitter are connected with the battery terminals as shown below:<\/p>\n

\"Circuit<\/p>\n

Figure 5:\u00a0 NPN Transistor Circuit Diagram<\/p>\n

The majority of charge carriers in the emitter, i.e., electrons, flow towards the base, which is p-type and is positive. The flow of electrons is known as current, so the flow of electrons from emitter to base is referred to as emitter current or IE.<\/sub><\/p>\n

The base has less number of holes as it is lightly doped and is narrow as compared to the emitter and collector. Consequently, few electrons will combine with the holes, and the majority of electrons will pass through the base. This resultant flow of electrons is called base current IB,<\/sub> and it is very small.<\/p>\n

The positive terminal of the battery will attract the remaining electrons. Consequently, the electrons will start flowing across the collector-base junction. This is known as collector current IC. <\/sub><\/p>\n

The relation between base current Ib, <\/sub>collector current IC, <\/sub>and emitter current IE <\/sub>is given by the following equation:<\/p>\n

IE <\/sub>= IB <\/sub>+ IC<\/sub><\/p>\n

In DC mode, the relation between\u00a0 IE <\/sub>and IC <\/sub>can be expressed in terms of DC gain as follows:<\/p>\n

IC = <\/sub>IE<\/sub><\/p>\n

For ideal cases, the value is equal to one. However, in practical cases, the value is between 0.90 to 0.998.<\/p>\n

In DC mode, the relation between\u00a0 IE <\/sub>and IC <\/sub>can be expressed in terms of DC gain as follows:<\/p>\n

Working of PNP Transistor:<\/h2>\n

PNP Transistor Configuration<\/h4>\n

In a PNP transistor, the collector and the emitter are doped with p-type impurity, whereas the base is doped with n-type impurity. This is shown in the figure below:<\/p>\n

\"pnp<\/p>\n

Figure 6: PNP Transistor Configuration<\/p>\n

PNP Transistor Symbol<\/h4>\n

The negative voltage is applied on the collector, and the direction of conventional current is from emitter to collector. The majority of charge carriers in p-type regions, i.e., emitter and collector, are holes, and minority charge carriers are electrons. The majority charge carriers in n-type regions, i.e., bases are electrons, and holes are minority charge carriers. Hence, the majority of charge carriers in a PNP transistor are holes. The symbol for the PNP transistor is shown below:<\/p>\n

\"pnp<\/p>\n

Figure 7: Symbol for PNP transistor<\/p>\n

Circuit Diagram for PNP Transistor<\/h4>\n

In the PNP transistor, two pn junctions are formed; one is the emitter-base junction, and the other is a collector-base junction.\u00a0 The transistor works in active mode, so the base-emitter junction is connected in a forward-biased configuration, and the collector-base junction is connected in a reverse-biased configuration through supply voltage. The collector and the emitter are connected with the battery terminals as shown below:<\/p>\n

\"pnp<\/p>\n

Figure 8: PNP Transistor Circuit Diagram<\/p>\n

When the positive voltage is applied to the emitter, the majority of charge carriers in the emitter, i.e., holes, flow towards the base, which is n-type and negative. The holes are attracted to electrons and flow towards the base. This flow of holes from emitter to base is referred to as emitter current or IE.<\/sub><\/p>\n

The base has fewer electrons as it is lightly doped and narrower than the emitter and collector. Consequently, few holes will combine with the electrons, and the majority of holes will pass through the base. This resultant flow of holes is called base current IB,<\/sub> and it is very small.<\/p>\n

The negative terminal of the battery will attract the holes. Consequently, the holes will start flowing across the collector-base junction. This is known as collector current IC. <\/sub><\/p>\n

The relation between base current Ib, <\/sub>collector current IC, <\/sub>and emitter current IE <\/sub>is given by the following equation:<\/p>\n

IE <\/sub>= IB <\/sub>+ IC<\/sub><\/p>\n

The following equation gives the collector current:<\/p>\n

IC <\/sub>= IE <\/sub>\u2013 IB<\/sub><\/p>\n

The base current is generally 2% of the emitter current, and the collector current is 98% of the emitter current.<\/p>\n

Differences Between PNP and NPN Transistors:<\/strong><\/h2>\n

The major differences between PNP and NPN transistors are as follows:<\/p>\n