How Do You Solve a Basic BJT Problem Using KVL?

  • Thread starter dennislam
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    Bjt Npn
In summary, the conversation discusses a problem involving a circuit with a common base configuration. The person attempting the problem used KVL to solve for i_e, but got stuck when trying to find i_c and use KVL around the CE and CB loops. They also mention confusion about the relationship between Vce and Vcb and the operating mode of the transistor. Another person suggests that the problem may involve a mistake with the polarity of the emitter bias voltage.
  • #1
dennislam
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1

Homework Statement


bjt q5.png


Homework Equations


KVL

The Attempt at a Solution


Using KVL around BE loop
0-0.6-i_e*(30*10^3)-15=0
i_e=-0.52mA
However, I stuck when I tried to find i_c and use KVL around CE loop/ CB loop
For CE loop:
10-i_c*(15*10^3)-Vce-i_e*(30*10^3)-15=0
For CB loop:
10-i_c*(15*10^3)-Vcb=0
I got confused about how to relate Vce and Vcb. (here I guess it must be some kind of relationship that looks like Vbc-Vac=Vba)
Also, it seems like it is operating in cutoff mode (both Vc and Ve>Vb), however, there is current flowing around the loop. So what is the mode that the transistor is actually operating in?
Thank you!:confused:
 

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  • #2
Circuit looks odd to me. Like common base configuration but the polarity of the emitter bias voltage is wrong ( should be -15v). Think the transistor is either off or they made a mistake?

Otherwise I would suggest you assume Ic=Ie.
 
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  • #3
Yes, try reversing the polarity of the 15v supply.
 

1. What is KVL and why is it used in solving basic BJT problems?

KVL stands for Kirchhoff's Voltage Law, which states that the algebraic sum of voltages around a closed loop in a circuit must equal zero. In basic BJT problems, KVL is used to determine the voltage drops across different elements in the circuit, which is necessary for calculating the current flow and analyzing the behavior of the BJT.

2. How do you apply KVL in solving basic BJT problems?

To apply KVL, you must first identify all the loops in the circuit and assign a direction for the current flow in each loop. Then, write an equation for each loop by summing up the voltage drops across all elements in that loop. Finally, solve the resulting system of equations to find the values of the unknown voltages in the circuit.

3. Can KVL be used in any type of BJT circuit?

Yes, KVL can be applied in any type of BJT circuit, including common emitter, common base, and common collector configurations. However, the specific equations and calculations may vary depending on the type of circuit and the given parameters.

4. Can KVL be used to solve BJT problems with multiple BJTs in the circuit?

Yes, KVL can be used to solve BJT problems with multiple BJTs in the circuit. However, it may become more complex as the number of elements and loops in the circuit increases. In such cases, it may be helpful to use a systematic approach, such as nodal analysis, to simplify the calculations.

5. Are there any limitations to using KVL in solving basic BJT problems?

While KVL is a useful tool for solving basic BJT problems, it does have some limitations. It assumes ideal circuit conditions, such as linear relationships between voltage and current, and does not account for non-idealities like parasitic elements. In addition, KVL may not be sufficient for analyzing more complex BJT circuits, and other methods, such as the small-signal model, may be necessary.

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