PNP vs. NPN: What Are the Important Differences?

Modern electronics overwhelmingly rely upon the transistor. Each circuit board has its own logical flow, with clearly defined circuit paths to route electricity. Devices like computers certainly have their own logic. It does require specialty transistors to apply this logic, however. A computer’s bare metal logic is formed using a network of transistors, which help to route voltages through components.

Two of the most commonly used transistors in modern electronics are the PNP and NPN. These transistor types have been in use since the introduction of the transistor. Why would use one over another? Let’s take a closer look at the key differences between these two transistor types and their usage.

PNP and NPN Transistors: Side-By-Side Comparison

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03/28/2023 09:50 pm GMT

PNP vs. NPN: What’s the Difference?

A Brief Overview

Bell Telephone Laboratories developed the first transistor in 1948. Often lauded as the most important invention in modern history, the introduction of the transistor had a massive impact on electronics. Bell’s invention would lead to explosive growth in technology. Such growth saw the rise of miniaturization and more complex machines being built without relying on antiquated technologies like the cathode tube.

The invention of the transistor gave way to the electronic age. Transistors have two main operating types, Positive-Negative-Positive and Negative-Positive-Negative, or PNP and NPN. You can also refer to these transistors as BJTs or bipolar junction transfers. All electronics use PNP or NPN transistors, and in the case of complex electronics like a computer, it will use both.

Both transistor types commonly used germanium as their material. This moved to silicon for the sake of durability and longevity when exposed to heat.

What is a PNP Transistor?

As previously mentioned, a PNP transistor is short for Positive-Negative-Positive. What this means in practice is that the electrons present in the wafers of the semiconductors flow from positive charge to positive charge, using the negative layer sandwiched in between as a transfer medium. Transmission of electrons occurs with the application of a negative charge to the base pin of the transistor. This allows for the positively charged electrons to flow through a hole of sorts in the negative layer.

There are certain drawbacks to using a PNP transistor. Transferring positive electrons for the transistor is slower than other methods. Couple this with the fact that good quality PNP transistors are more expensive than their NPN counterparts, and it begs the question of where one might see their use in a modern device. While PNPs are less common in simpler electronics, they still have a utility.

PNP transistors also require the usage of identical voltages when routing logic to a device. For a simplified example, you could only route the signal flow of voltage from a 5-volt device to another 5-volt device.

What is an NPN Transistor?

A Negative-Positive-Negative or NPN transistor is the most common type of transistor you’ll find in modern devices. After doping, or contaminating, the base layers of the transistor, it uses a positively charged layer between the two negatively charged outer layers to quickly transmit electrons. These generally operate at a faster rate than a PNP transistor.

There is no implicit requirement for an NPN transistor to match the voltages between devices. This is handy for devices that need switching, as it doesn’t require additional signals to cut the voltage like you would on a PNP transistor. NPN transistors remain the most commonly used transistor due to operating like a simple switch in theory.

PNP vs. NPN: Their Applications in Modern Electronics

While NPN transistors remain the norm for modern electronics, it is more common to utilize both transistor types when creating the logic flow. Certain electronic devices will often call for both types of transistors, like a guitar amplifier for example. Some guitar amplifiers will utilize something called a push-pull pot, which can introduce more distortion to the audio. Push-pull pots will overwhelmingly use a PNP transistor to introduce the extra current to the audio.

Earlier computers would use a combination of PNP and NPN transistors as well. In recent years, their usage for the core components of a CPU has largely been replaced by FETs, another type of transistor.

NPN and PNP transistors see more common use as sensors for modern automation purposes. Both transistors are great in use for proximity sensors. For hobbyists both remain popular as well and can directly integrate with microcontrollers like the Teensy and Arduino for creating complex routing for electronic projects.

While FETs have largely superseded them in the place of complex electronics like smartphones and computers, they still remain on the circuit boards. Certain basic elements like switches and other controls rely on the PNP and NPN transistors. They also still see usage in industrial applications, where they make for ideal sensors for heavy machinery operating. PNPs in particular are extremely popular for industrial usage, and remain the norm in American manufacturing for sensors.

Other Transistors

Aside from the ubiquitous PNP and NPN transistors, there are also field effect transistors or FETs. These operate similarly to PNP and NPN transistors but can operate at a much faster rate overall. You’ll typically FETs in consumer electronics, like smartphones, computers, tablets, and so on. FETs don’t need a sandwiched layer to operate in the same manner as a PNP and NPN but still have the same overall net effect.

FETs themselves predate the concept of the semi-conductive transistor as implemented by Bell Telephone by thirteen years, with the initial plans drawn up by Heil in 1935. The actual concept itself wouldn’t be ready for manufacture until the 1960s when viable and widely available FETs entered the market.

The basic operation of a FET is a little more robust in a sense than a PNP or NPN transistor. FETs have three electrodes, as well as something called a gate. One of the electrodes is called the drain and the other is the source. The gate controls the flow of electrons and can be positively or negatively charged. This leads to some FETs being labeled as P-Channel and N-Channel respectively. These operate similarly to PNP and NPN transistors in concept, but they have a much higher impedance. This effectively means they can handle far more current than a typical logic transistor like the aforementioned PNP or NPNs.

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03/28/2023 09:57 pm GMT

PNP vs. NPN: 4 Must-Know Facts

• All electronics use PNP or NPN transistors, and complex electronics like a computer will use both.
• Good-quality PNP transistors are typically more expensive than their NPN counterparts.
• NPN transistors are the most commonly used transistor due to operating like a simple switch in theory.
• PNP and NPN transistors have largely been superseded by FETs in the place of complex electronics like smartphones and computers, but PNP and NPN still remain on the circuit boards.

PNP vs. NPN: Which Transistor is Better?

There isn’t necessarily a better or worse transistor for an electronic project. Instead, it is more about what is applicable to the design of the logic implemented at a hardware level. FETs are overkill for a light switch, but NPNs or PNPs aren’t robust enough to handle the voltage powering a computer or power drill. Keeping this in mind, it is more about picking what is most efficient for a given design.

NPN and PNP transistors may not be the latest and greatest on the market these days, but they are still great choices for certain designs. They still see a fair amount of usage in industrial applications for example, where the sturdy and steadfast logic they can implement proves vital for the many sensors at work with heavy machinery. Chances are you interact with devices using this very same system of logic on a day-to-day basis.