In BJT Ie=Ib+Ic ; Ie-emitter current; Ib-base current; Ic-collector current

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In summary: BJT The collector region is larger in BJT because it is designed to have a larger area to collect charge carriers. This helps to increase the current gain and overall performance of the BJT.3). why the collector region is moderately doped when compared to highly doped emitterThe collector region is moderately doped when compared to the highly doped emitter because it allows for a larger depletion region between the base and collector, which helps to prevent leakage current and improve the BJT's performance. Additionally, a larger collector region allows for a larger area to collect charge carriers, resulting in higher current gain.
  • #1
kpraneethin00
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I have three doubts in BJT:
1). in BJT Ie=Ib+Ic ; Ie-emitter current; Ib-base current; Ic-collector current
then i find in many circuits, collector current is given to load, if the emitter current is greater than the collector current, we can connect the emitter terminal to the load, to get more current...

2). why the collector region is large in BJT

3). why the collector region is moderately doped when compared to highly doped emitter
Please help me in this
 
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  • #2
kpraneethin00 said:
I have three doubts in BJT:
1). in BJT Ie=Ib+Ic ; Ie-emitter current; Ib-base current; Ic-collector current
then i find in many circuits, collector current is given to load, if the emitter current is greater than the collector current, we can connect the emitter terminal to the load, to get more current...
Sometimes we connect the load to emitter, Google emitter follower. But then we lose the voltage gain.
Also kept in mind that the emitter current is greater than the collector current just by a small amount of a base current. So for BJT that have a large current gain β the difference is not significant. Ic/Ie = β/(β+1) for β = 100 -->Ic/Ie = 100/101 = 0.990099009
 
  • #3
kpraneethin00 said:
2). why the collector region is large in BJT

3). why the collector region is moderately doped when compared to highly doped emitter
Please help me in this

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http://hyperphysics.phy-astr.gsu.edu/hbase/solids/trans2.html
 
  • #4
kpraneethin00 said:
I have three doubts in BJT:
1). in BJT Ie=Ib+Ic ; Ie-emitter current; Ib-base current; Ic-collector current
then i find in many circuits, collector current is given to load, if the emitter current is greater than the collector current, we can connect the emitter terminal to the load, to get more current...
You have to be careful in how the BJT works. Collector current IS CONTROLLED by the emitter current. You design the circuit to setup the emitter current to get the collector current. Collector has very high output impedance where emitter is very low output impedance. Collector is a controlled current source and emitter is a voltage source. Collector current is controlled by the Vbe drop. Yes, Ie=Ib+Ic, but

[tex]I_c=I_s e^{[\frac{V_{BE}}{V_T}]}[/tex]

Emitter being a voltage source, the current is govern by the voltage drop across the resistor connects to the emitter. Collector current reflects the emitter current.
 
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  • #5


I would like to address your doubts in BJT and provide some explanations.

1) In BJT, the equation Ie=Ib+Ic represents the principle of current conservation, where the total current entering the emitter (Ie) is divided into two parts - the base current (Ib) and the collector current (Ic). This is due to the fact that the base-emitter junction acts as a forward biased diode, allowing a small current (Ib) to flow from the base to the emitter. The majority of the current (Ic) flows from the collector to the emitter, making it the dominant current in most cases. Therefore, in circuits where the collector current is used to drive a load, it is often larger than the base current.

2) The size of the collector region in a BJT is typically larger than the base and emitter regions because it is responsible for collecting the majority of the current (Ic) flowing through the device. This region is designed to have a larger area to increase the chances of current carriers (electrons or holes) reaching the collector and reducing the chances of recombination. This is important for maintaining a high collector current and improving the overall performance of the BJT.

3) The collector region is moderately doped compared to the highly doped emitter region for several reasons. First, a moderate doping level allows for a good balance between conductivity and avoiding the formation of a reverse-biased p-n junction at the base-collector junction. This ensures that the collector region can efficiently collect the majority carriers without interfering with the operation of the device. Additionally, a moderate doping level also helps to reduce the chances of recombination in the collector region, which would decrease the overall current gain of the BJT.

I hope this helps to clarify your doubts and provides a better understanding of BJTs. Keep exploring and asking questions to deepen your understanding of this important electronic device.
 

1. What is the significance of Ie=Ib+Ic in BJT?

The equation Ie=Ib+Ic represents the principle of current conservation in a BJT (bipolar junction transistor). It states that the total current flowing into the emitter (Ie) is equal to the sum of the currents flowing into the base (Ib) and the collector (Ic). This equation is used to analyze the behavior and performance of BJTs in electronic circuits.

2. How is Ie, Ib, and Ic related in a BJT?

In a BJT, the emitter current (Ie) is the sum of the base current (Ib) and the collector current (Ic). This relationship is given by the equation Ie=Ib+Ic. The base current controls the flow of electrons from the emitter to the collector, while the collector current is the main current flowing through the BJT.

3. What is the difference between Ie, Ib, and Ic in a BJT?

Ie, Ib, and Ic represent the different currents flowing in a BJT. Ie is the total current entering the emitter, Ib is the current entering the base, and Ic is the current entering the collector. The base current controls the flow of electrons from the emitter to the collector, while the collector current is the main current flowing through the BJT. The emitter current is the sum of both these currents.

4. How do changes in Ie, Ib, and Ic affect the performance of a BJT?

Changes in the values of Ie, Ib, and Ic can significantly affect the performance of a BJT. The base current (Ib) is used to control the collector current (Ic), so any changes in Ib will result in corresponding changes in Ic. Changes in the emitter current (Ie) can also affect the overall gain and stability of the BJT. Therefore, it is crucial to carefully analyze and control these currents in electronic circuits.

5. What is the role of Ie, Ib, and Ic in amplifier circuits using BJTs?

In amplifier circuits using BJTs, Ie, Ib, and Ic play crucial roles. The base current (Ib) controls the collector current (Ic), which in turn determines the amplification of the input signal. The emitter current (Ie) also affects the overall gain and stability of the amplifier. By carefully controlling these currents, amplifiers can be designed to have specific gain and frequency response characteristics.

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