Introduction to 2n4402

Introduction to 2n4402

• 2n4402 is a bipolar silicon transistor, where one layer of N doped semiconductor is sand-witched between the two layers of P doped semiconductor.
• It works in a way, the small current at the end of the base is used to control a large amount of current at the end of collector and emitter.

• PNP transistor works in a similar way to NPN transistor with the exception of current carriers. In case of NPN transistors, current carriers are electron while current carriers in the case of PNP transistors are holes and direction of current and polarities of voltage will be reversed in this case.
• In PNP transistor, P letter represents the polarity of voltage applied to the emitter which is positive and N letter shows the polarity of voltage applied to the base which is negative. In order to conduct in PNP transistor, Emitter will always be more positive than base and collector.

2n4402 Pinout

• 1: Emitter
• 2: Base
• 3: Collector

• Unlike NPN transistors, here current flows from emitter to collector and current carriers are holes.

PNP Circuit Symbol

• Following is the circuit symbol of PNP transistor. It consists of two P layers and one N layer.

• The polarity at the emitter side is positive with respect to both base and collector.
• The base of this transistor is negative with respect to emitter.
• Current flowing through the emitter side is the sum of current flowing through collector and base.
• Small amount of current at the base side is used to control the large amount of current at the collector and emitter side.
• PNP and NPN works in similar way with the exception of current direction and medium used for the flow of current.
• In PNP transistor current flows from emitter to collector and current carriers in this case are holes which are collected by the collector.

PNP Transistor Configuration

• Transistor configuration of PNP 2n4402 transistor is shown in the figure below:

• Emitter is positive with respect to collector and base
• Small amount of base current is used to control the large current at the collector and emitter side.
• Current carriers are holes which are collected by the collector.

Transistors as a Matched Switch

• In most of the cases, PNP transistors replace the NPN transistor with the only exception in the direction of current and polarities of voltages.
• Like NPN transistor, PNP transistor can also be used as a switching device.
• You might think what is the point of using PNP transistor while there are lots of NPN transistors out there that can be used as a switch or for amplification purpose. However, taking two types of transistors come with a lot of advantage in designing the power amplifier circuit.
• Class B-amplifiers come with a two pair of NPN and PNP transistor, where both transistors are used to control the current flowing in both directions at any instant of time. Transistors are called "Complementary Transistors" which use both NPN and PNP transistor of identical characteristics.
• In Class B-amplifiers, both transistors work in a similar way i.e. NPN transistors conducts for the positive half cycle and PNP transistor conducts for the negative half cycle of the transistor. This results in flowing the power at the load out put in both directions. PNP transistors will switch on when it sinks current to its base side and it will switch off when current at the base side stops to flow.

Applications of 2n4402

• These transistors are mainly used for voltage and power amplification.
• In combination with NPN transisters, these PNP transistors form a perfect bond through which current flows alternately from both sides of NPN and PNP transistors.