Introduction to 2n2907

Introduction to 2n2907

• 2n2907 is a PNP bipolar junction transistor which is mainly used for low power general purpose amplification and switching application.
• In this transistors, N layers is composed of semiconductor material which exists between the two layers of P type material.
• N side represent the base side and polarity will be negative at the base side.
• P side represents the emitter terminal and polarity at the emitter side will be positive.
• In order to conduct, base must be negative with respect to emitter.
• And collector-base junction will always be reverse biased so polarity must be reversed at the collector side. Collector is more negative with respect to base terminal.

• This transistor is a bipolar device, so conduction will be carried out by both charge carriers i.e. holes and electrons but majority charge carriers will be holes in this case.
• PNP and NPN transistors work in a similar fashion with some exceptions i.e. voltage polarities and current directions will be reserved in case of PNP transistors as compared to NPN transistors.
• Base is negative is PNP transistor while it is positive in case of NPN transistors.
• These transistors are termed as current controlled device because small current at the base side is used to control large current at the collector and emitter side.
• When we apply voltage at the base side it gets biased, and it allows the electrons to flow from emitter to collector.
• In case of PNP transistor, current will flow from emitter to collector but majority charge carriers will be holes which are then collected by the collector.

2n2907 Pinout

• The ability of base current to control large current at the emitter and collector side is used for amplification purpose.
• Emitter will be highly doped and base will be lightly doped.
• Collector and emitter are different to each other with respect to their size and doping concentration. Collector will also be lightly doped as compared to emitter.

Circuit Diagram of 2n2907

• Current at the emitter side is the combination of base and emitter current.
• This transistor comes in TO-92 casing and can be manufactured with different pin configurations.
• In case of PNP transistor, holes are transferred internally which then allow the current to flow in the external circuit. In case of NPN transistors, electrons flow externally and conduction is carried out from emitter to collector.
• Both NPN and PNP transistor work in a same fashion but medium used for conduction is different. Most of the professionals prefer NPN transistors over PNP transistors because they consider, conduction through mobility of electrons is better than conduction through mobility of holes.
• However, both transistors come with a lot of advantage and can be used for similar applications.

Absolute Maximum Ratings of 2n2907

• These are the stress rating above which device can be completely damaged.
• Similarly, if stresses are applied for extended period of time, they can harm the device reliability. It is advised to keep the operating conduction within the range of absolute maximum ratings.

Combination of NPN and PNP Transistors

• Both NPN and PNP transistors are used in combination with each other.
• These transistors are incorporated perfectly to design a power amplifier output circuit which helps in generating the ideal output.
• Transistors that used combination of NPN and PNP transistos are called Complementary Transistors.
• Both NPN and PNP transistors  are widely used in Class B amplifiers where both transistors help in controlling the current flowing in both directions at any time.

Applications

• This transistor is mainly used for switching and linear amplification.
• Analog amplification also involve this type of transistor.