# Collector Current through BJT Circuit

• Engineering
• curiousguy23
In summary, the conversation discusses a circuit with an unknown resistance that needs to be found. The equations used include Vth, Rth, Vbe, Beta, Vcc, IL, Ib, and Ie. The solution involves substituting values into the equation and solving for IL, which yields a value of 4.15mA. However, the tutor believes the correct answer is 4.3mA and explains that this difference is due to the base current pulling down the voltage.
curiousguy23

## Homework Statement

Consider the following circuit
http://img109.imageshack.us/img109/80/circuit1.jpg

IL, current through R3 (unknown resistance must be found)

## Homework Equations

Vth=(Vcc/Rtotal)*R1 (V tThevenin)

Rth=R1//R2 (R Thevenin)

Vbe= 0.7 volts (silicon diode)
Beta (transistor constant)=100
Vcc=10v
IL=Beta*Ib
Ie=Ib + IL

## The Attempt at a Solution

I used the following Equation to try and obtain an answer.

Vcc= (Ib*Rth)+ (Ie*R4) + Vbe + Vth

Vth=5v
Rth=2.5k Ohms

Substituting gives:

10=(IL/Beta)*(2.5k) + 1000*(IL*((Beta +1)/Beta)) + 0.7 + 5

This yields an answer of IL=4.15mA.

My tutor said this is a wrong answer, the correct one is 4.3mA
What is wrong in my reasoning/Working?

Last edited by a moderator:

The tutor has just taken 0.7 V from the 5 V at the center of the two 5K resistors and said this must be the voltage across the emitter resistor.

But the base current pulls this voltage down a little and that makes the difference between your answers.

THanks,

I just realized what he did,

He assumed Ie=IL and Ib=0 since it is very small.

## 1. What is a BJT circuit?

A BJT (Bipolar Junction Transistor) circuit is a type of electronic circuit that uses a semiconductor device called a transistor to amplify or switch electronic signals. It is commonly used in a variety of electronic devices, such as amplifiers, oscillators, and digital logic circuits.

## 2. What is collector current?

Collector current is the flow of electric current through the collector terminal of a BJT transistor. It is the sum of the base and emitter currents and is controlled by the amount of current flowing into the base terminal.

## 3. How is collector current calculated?

The collector current can be calculated using Ohm's law, which states that the current (I) flowing through a conductor is equal to the voltage (V) divided by the resistance (R). In a BJT circuit, the collector current (Ic) is equal to the voltage applied to the collector terminal (Vc) divided by the resistance of the circuit (Rc).

## 4. What factors affect collector current in a BJT circuit?

The collector current in a BJT circuit is affected by the base current, the voltage applied to the collector terminal, and the resistance of the circuit. It is also influenced by the characteristics of the transistor, such as its gain and saturation current.

## 5. How can collector current be controlled in a BJT circuit?

The collector current in a BJT circuit can be controlled by varying the base current or the voltage applied to the collector terminal. It can also be controlled by using a resistor in the circuit to limit the amount of current flowing through the transistor. Additionally, the use of feedback circuits and biasing techniques can also help regulate the collector current.

Replies
5
Views
2K
Replies
23
Views
3K
Replies
8
Views
1K
Replies
4
Views
2K
Replies
14
Views
3K
Replies
7
Views
5K
Replies
10
Views
1K
Replies
3
Views
2K
Replies
4
Views
2K
Replies
1
Views
2K