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Aditya Mysore
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Does the collector current in a transistor depend on the base-collector voltage in a common base configuration? If so,how does it depend mathematically?
Thanks. Can you also explain physically why it does not depend on the voltage of the other junction?LvW said:The principle behaviour of a BJT does not depend on the specific configuration (common emitter, base or collector).
In any case, the famous Shockley equation applies: Ic=Is[exp(Vbe/VT) -1].
Hence, the collector current always is determined and controlled by the base-emitter voltage only.
I am aware that in some textbooks and other publications (in particular: Internet) it is stated that Ic would be controlled by Ib because of the relation Ic=B*Ib.
This relation holds, of course, and it is often used for designing simple transistor stages - however, it does not tell anything about cause and effect.
There are many properties and effects to be observed in BJT applications that can be explained ONLY with the above mentioned equation Ic=f(Vbe).
(I would not be surprised if this reply would cause some disagreements from other forum members; I have corresponding experiences.).
Aditya Mysore said:Thanks. Can you also explain physically why it does not depend on the voltage of the other junction?
A bipolar junction transistor is a type of semiconductor device that is used to amplify and switch electronic signals. It is made up of three regions - the emitter, base, and collector - and can be either NPN or PNP type. BJTs are commonly used in a variety of electronic devices, from computers to audio amplifiers.
A BJT works by controlling the flow of current through its three regions. The base-emitter junction acts as a diode, allowing current to flow only in one direction. When a small current is applied to the base, it changes the characteristics of the base-collector junction, allowing a larger current to flow from the collector to the emitter. This amplifies the signal, making it useful for switching and amplification purposes.
The main difference between these two types of BJTs is the direction of current flow. In an NPN transistor, current flows from the collector to the emitter, while in a PNP transistor, current flows from the emitter to the collector. This also affects the polarity of the voltage applied to the base in order to switch the transistor on or off.
BJTs have several advantages, including high current gain, fast response time, and the ability to handle high power levels. They are also relatively inexpensive and easy to manufacture, making them a popular choice for a variety of electronic applications.
BJTs are used in a wide range of electronic devices and circuits, including amplifiers, switches, oscillators, and digital logic circuits. They are also commonly used in power supplies, audio equipment, and communication systems.