Simple Transistor: Basics, Types & Uses

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In summary, the conversation discussed a circuit problem involving the calculation of VB, taking into account the loading of the bias network by the BJT. The participants suggested using nodal analysis and thevenin's theorem to solve the problem. The correct KVL equation for the circuit was also provided.
  • #1
Duave
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  • #2
Your answer is not correct. You forget about 150K resistor.

Maybe this circuit will be easy for you to solve, you can even use nodal analysis.

attachment.php?attachmentid=67808&stc=1&d=1395236790.png


Also notice that I1 = (Ib + I2)

Or you can replace voltage divider with his thevenin equivalent circuit.
 

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  • #3
Jony130 said:
Your answer is not correct. You forget about 150K resistor.

Maybe this circuit will be easy for you to solve, you can even use nodal analysis.

attachment.php?attachmentid=67808&stc=1&d=1395236790.png


Also notice that I1 = (Ib + I2)

Or you can replace voltage divider with his thevenin equivalent circuit.

Here is a revised version of the solving for VB using KVL
This is question 2(a).

Thank you for any help that you can offer.

Did I answer the question correctly and thoroughly? Can you please find any errors, and point them out to me so that I can fix them?

Homework Statement



2(a): Calculate VB including loading of the bias network by the BJT

Homework Equations



IE = IC + IB
............
VCC-(IB)(RB) -(IE)(RE)-(VBE) = 0
...................


The Attempt at a Solution




https://scontent-b.xx.fbcdn.net/hphotos-frc1/t1.0-9/1964876_10151943479145919_1107480603_n.jpg


Is the answer correct for V(B)? If not, where are the errors located?

Thanks again for your help.
 
  • #4
Duave said:
IE = IC + IB
............
VCC-(IB)(RB) -(IE)(RE)-(VBE) = 0
...................

.
You have error already in the the second expression. Are you sure that this is correct KVL/KCL for this circuit? Can you tell me where do you see RB resistor in this circuit ?
The KCL for VB node is I1 = I2 + Ib

Or why you don't try to use thevenin's theorem and replace R1 and R2 and Vcc with his equivalent circuit (Rth and Eth)?
 
  • #5
Jony130 said:
You have error already in the the second expression. Are you sure that this is correct KVL/KCL for this circuit? Can you tell me where do you see RB resistor in this circuit ?
The KCL for VB node is I1 = I2 + Ib

Or why you don't try to use thevenin's theorem and replace R1 and R2 and Vcc with his equivalent circuit (Rth and Eth)?

Could Rb= Rb1||Rb2?
 
  • #6
Jony130 said:
You have error already in the the second expression. Are you sure that this is correct KVL/KCL for this circuit? Can you tell me where do you see RB resistor in this circuit ?
The KCL for VB node is I1 = I2 + Ib

Or why you don't try to use thevenin's theorem and replace R1 and R2 and Vcc with his equivalent circuit (Rth and Eth)?


How many loops do you have with KVL?
 
  • #7
Two loops:
First loop
Vcc = I1*R1 + I2*R2
And the second one
I2*R2 = ??

Or we can use nodal equation

(15V - Vb)/130k = Vb/150k + Ib

Where Ib = ??

Duave said:
Could Rb= Rb1||Rb2?
Yes, but what about Vcc ?
 
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  • #8
Jony130 said:
Two loops:
First loop
Vcc = I1*R1 + I2*R2
And the second one
I2*R2 = ??

Or we can use nodal equation

(15V - Vb)/130k = Vb/150k + Ib

Where Ib = ??Yes, but what about Vcc ?
I don't understand,

Wouldn't it be :

Vcc - Ib(R1||R2) - IeRe - Vbe = 0

and
Vcc = I1*R1 + I2*R2
 
  • #9
Duave said:
I don't understand,

Wouldn't it be :

Vcc - Ib(R1||R2) - IeRe - Vbe = 0

and
Vcc = I1*R1 + I2*R2
No this is incorrect because Ib current flows only through R1 resistor.
But we can use Rb = R1||R2 if you replace R1 and R2 voltage divider with his thevenin's equivalent circuit.
 
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  • #10
Duave said:
...

Do *NOT* remove content from your posts. Check your PMs.
 
  • #11
Jony130 said:
No this is incorrect because Ib current flows only through R1 resistor.
But we can use Rb = R1||R2 if you replace R1 and R2 voltage divider with his thevenin's equivalent circuit.

you please just tell me the KVL for this circuit again. I cannot obtain an official answer anywhere. I've been working on this problem for four days and it's only worth two points. I don't get it, and I need it to be laid out without anymore theory, on math.

You've been a big help. Could you show me both of the KVLs for this circuit

thank you
 
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FAQ: Simple Transistor: Basics, Types & Uses

1. What is a transistor and how does it work?

A transistor is a semiconductor device that is used to amplify or switch electronic signals. It consists of three layers of a material called a semiconductor, with each layer being either positively or negatively charged. By applying a small electrical current to the middle layer, known as the base, the transistor can control the flow of a larger current between the other two layers, known as the collector and emitter. This allows the transistor to act as a switch or an amplifier.

2. What are the different types of transistors?

There are two main types of transistors: bipolar junction transistors (BJTs) and field-effect transistors (FETs). BJTs are further divided into NPN and PNP transistors, which differ in the direction of current flow. FETs are divided into JFETs (junction field-effect transistors) and MOSFETs (metal-oxide-semiconductor field-effect transistors). Each type of transistor has its own unique characteristics and uses.

3. What are the common uses of transistors?

Transistors are used in a wide range of electronic devices, including computers, televisions, radios, and smartphones. They are also used in power supplies, motor control circuits, and audio amplifiers. In addition, transistors are an essential component in digital logic circuits, which are the building blocks of modern computers and other digital devices.

4. How do I choose the right transistor for my project?

The type of transistor you choose will depend on the specific requirements of your project. Some factors to consider include the desired voltage and current levels, switching speed, and power dissipation. It is also important to consider the transistor's datasheet, which provides detailed information about its characteristics and capabilities.

5. Can transistors be used in both AC and DC circuits?

Yes, transistors can be used in both AC and DC circuits. However, the type of transistor and its configuration may differ depending on the type of circuit. For example, NPN transistors are commonly used in DC circuits, while JFETs are often used in AC circuits. It is important to consult the datasheet and understand the characteristics of the transistor before using it in a circuit.

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