NPN vs PNP Transistor: What is the difference between them?

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What is a transistor?

A transistor is a three-terminal electronic component that can be used to control the flow of electricity. It was the first electronic component to have the ability to switch or amplify an electric current. Although there are other types of transistors, bipolar junction transistors are still commonly employed in digital circuits because they are a straightforward technology that may be utilized to build sophisticated electronic circuits. One of the greatest discoveries of the 20th century was the transistor. From computers and cellphones to cars and airplanes, they are found in almost every electrical gadget. In order to create the intricate electronic circuits that run our contemporary world, transistors—which are tiny switches that regulate the flow of electricity—are necessary.

What are the two basic types of transistors?

Bipolar junction transistors (BJTs) The base, emitter, and collector are the three semiconductor layers that make up a BJT. Electrons are emitted by the emitter, are controlled by the base in their movement between the emitter and collector, and are then collected by the collector. To control the movement of a larger current from the emitter to the collector, BJTs use a tiny base current. Current amplification is what is occurring here. BJTs are a common component in many different types of electronic devices, such as computers, smartphones, and televisions.

NPN bipolar junction transistor

PNP bipolar junction transistor

Field-effect transistors (FETs) The source, gate, and drain are the three semiconductor layers found in FETs. The gate regulates the current flow between the source and drain, the two terminals through which the current flows. The electric field at the gate of a FET is used to regulate the current flow between the source and drain. The term for this is field-effect control. Electronic gadgets such as computers, cell phones, and digital circuitry all make use of FETs. The optimum transistor type for a given application will depend on the demands of that application. FETs are typically better for switching signals than BJTs are for signal amplification.

Who invented the transistor?

John Bardeen, Walter Brattain, and William Shockley of Bell Labs created the transistor in 1947. Their innovation transformed the electronics sector and laid the way for creating contemporary computers and other electronic devices.

What does a transistor do?

A transistor is a semiconductor device that has the ability to switch or amplify electronic signals. It is made up of a collector, a base, and an emitter, three doped semiconductor layers. A little voltage provided to a transistor's base allows a significantly bigger current to flow from the collector to the emitter. Transistors are extremely beneficial in electrical circuits due to their amplification effect.

How does a transistor work?

A tiny current at the base of a transistor controls the amount of current that flows between the emitter and collector. The transistor is off when there is no current at the base and no current passes from the emitter to the collector. The transistor is turned on and current can flow from the emitter to the collector when a modest current is applied to the base. It follows that the amount of current flowing from the base to the emitter is proportionate to the amount flowing from the collector to the emitter. As a result, a modest base current can regulate a much greater collector current. For signal amplification, transistors are extremely helpful for this reason. Switches can also be created using transistors. No current flows from the emitter to the collector when the base current is switched off, which also turns off the transistor. Current travels from the emitter to the collector when the transistor is activated by the base current. Because they can represent the binary numbers 0 and 1, transistors are perfect for use in digital circuitry.

How to test a transistor?

Identify the transistor pins: The emitter, base, and collector pins of a transistor are the three pins that it generally has. Use a multimeter in diode mode to locate these pins or see the transistor datasheet. Typically, the base and collector are connected to the smaller pins, with the emitter being attached to the largest pin.
Set up the multimeter: If available, switch your multimeter to the hFE (current gain) or diode test modes. Make sure the positive lead of the multimeter is connected to the anode and the negative lead to the cathode when utilizing the diode test mode.
Test the base-emitter junction: Placing the multimeter probes over the transistor's base-emitter junction will allow you to test the base-emitter junction. The positive lead of the multimeter should be linked to the base of an NPN transistor, and the negative lead should be connected to the emitter. The connections are the opposite in a PNP transistor. If the junction is working properly, the multimeter should show a voltage drop of approximately 0.6 to 0.7 volts. The junction could be defective if the voltage drop differs noticeably from what is expected or if there is no voltage drop.
Test the base-collector junction: The base-collector connection should be tested by repeating the procedure. The base of an NPN transistor should be linked to the positive lead of the multimeter, and the collector should be connected to the negative lead. Reversed connections are used in PNP transistors. If the junction is operating properly, the multimeter should show a voltage drop similar to the base-emitter junction (between 0.6 and 0.7 volts). The junction could be defective if there is no voltage drop or a voltage drop that is significantly different.
Test the hFE (current gain): If your multimeter has a transistor hFE test mode, you may use it to determine the current gain of the transistor. This is known as testing the hFE (current gain). To do this test, adhere to the instructions that came with your multimeter. The hFE value of a healthy transistor should fall within the parameters listed in the datasheet.
Additional tests: You can run more complex tests to evaluate the performance of the transistor if you have access to an oscilloscope or a transistor tester, including measuring the gain-bandwidth product or looking for leakage currents.

To test the transistor, remember to unplug it from all power sources. Additionally, bear in mind that while these methods offer a broad framework for testing transistors, the precise processes may vary based on the type of transistor and the tools you have access to.

NPN transistors

The most prevalent kind of transistors are NPN transistors. They are composed of three semiconductor layers, with an N-type layer sandwiched between two P-type layers in the center. A little positive voltage is given to the base terminal of an NPN transistor to turn it on. As a result, electrons move in the opposite direction, from the emitter terminal to the base terminal. The current then flows from the emitter to the collector as the electrons pass through the base terminal and reach the collector terminal. The transistor switches off when either no voltage or a negative voltage is delivered to the base terminal. This is due to the fact that the electrons cannot move from the emitter to the base.

NPN transistor symbol

PNP transistors

Even though PNP transistors are less prevalent than NPN transistors, electrical circuits nevertheless frequently use them. Three layers of semiconductor material, one P-type layer sandwiched between two N-type layers, make up PNP transistors. A tiny negative voltage is used to activate a PNP transistor by applying it to the base terminal. The emitter terminal to the base terminal starts to fill with holes as a result. The holes then provide a current flow from the emitter to the collector terminal by passing through the base terminal. The transistor switches off if a positive voltage or no voltage is provided to the base terminal. This occurs as a result of the holes' inability to go from the emitter to the base.

PNP transistor symbol

Video related to NPN and PNP Transistors

Differences between NPN and PNP transistors

One of the main differences between these two transistors is that when a positive supply is given to the base terminal of the NPN transistor, the flow of current will be between the collector and emitter terminals. When a negative supply is given to the base terminal of a PNP transistor, the charge carrier supplies move from the emitter terminal to the collector. In tabular form, many parameters are used to discriminate between NPN and PNP transistors. The key differences between NPN and PNP transistors are the following:

The NPN and PNP transistor symbols are nearly identical; the main distinction is the arrow's direction, which is based on the emitter. The arrow goes inside in a PNP transistor and moves outward to the base in an NPN transistor.
The PNP transistor is activated when holes enter the base, whereas the NPN transistor is activated when electrons enter the base.
The inside current in NPN transistors is caused by the shifting positions of the electrons, whereas the inside current in PNP transistors is caused by the shifting positions of the holes.
The output current in NPN transistors is created by the flow of holes, whereas in PNP it is created by the flow of electrons.
For NPN transistors, the minority charge carrier is a hole, while for PNP transistors, it is an electron.
Because an electron serves as the main charge carrier in an NPN transistor, its switching time is longer than that of a PNP transistor.
Both the NPN and PNP transistors have a connection that is forward-biased at the emitter-base junction.
The NPN and PNP transistors' collector-base junctions are reverse-biasedly linked.

Applications of NPN and PNP transistors

NPN and PNP transistors are used in a wide variety of electronic applications. Some common examples include:

Amplifiers
Switches
Logic gates
Power supplies
Motor controllers
Sensors

Applications of NPN transistor

Primarily used for switching reasons.
They are utilized in a Darlington pair setup to amplify weak signals.
In circuits where we must drain the current.
Additionally, they are utilized in temperature sensor circuits.
They can function effectively in situations requiring very high frequencies.
Used in logarithmic converters.

Applications of PNP transistor

They are mostly used as switches.
In amplification circuits, they are employed.
They are used in multi-transistor circuits called Darlington pair circuits.
They are now also utilized in robotics.
Electric motor current flow is managed using PNP transistors.
PNP transistors are used in matched pair circuits to generate the required and simultaneous power.

Can NPN be used instead of PNP?

Yes, NPN transistors can be used in place of PNP transistors in some situations, but there are a few crucial things to bear in mind. These are the specifics:

Polarity: The polarity of the current flow distinguishes NPN and PNP transistors from one another. The current in an NPN transistor travels from the emitter to the base, and then to the collector. In a PNP transistor, the current travels from the emitter to the base before turning around and going to the collector. This indicates that the current polarities in the two different types of transistors are switched around.
Voltage Levels: Because of their differing polarities, NPN and PNP transistors require distinct voltage levels. When compared to the emitter, the base of an NPN transistor normally needs to be positive, whereas the base of a PNP transistor typically needs to be negative. As a result, the voltage levels and polarities of the circuit must be changed when an NPN transistor is used in place of a PNP transistor.
Circuit Modifications: If a PNP transistor is replaced with an NPN transistor, the circuit may need to be altered. To satisfy the NPN transistor's various polarities and voltage requirements, for instance, the biasing resistors and voltage sources may need to be reorganized or modified.
Current and Power Ratings: It's critical to confirm that the NPN transistor used as a stand-in can manage the circuit's necessary current and power levels. Verify the NPN transistor's maximum ratings on its datasheet and compare them to the specifications of the circuit.

In conclusion, even though NPN transistors can replace PNP transistors, careful attention to the polarity, voltage levels, circuit adjustments, and current/power ratings is required to ensure proper operation and compatibility with the circuit.

Conclusion

NPN and PNP transistors are two of the most important types of transistors. They are used in virtually every electronic device, from computers and smartphones to cars and airplanes. NPN transistors are more common than PNP transistors, but both types are essential for building the complex electronic circuits that power our modern world.