Help with bjt amplifier design

In summary, the conversation discusses how to find values for resistors and capacitors in a fixed bias circuit with a common emitter configuration. The transistor used has an hfe value of min(40) max(150), Vce=10V, and Ic=150mA. The attempt at a solution involves using the geometric mean to solve for the value of hfe and a voltage gain of 50. However, it is suggested to use negative feedback to reduce the range of the transistor gains for better performance. The conversation ends with a question about the input and output impedances of the amplifier.
  • #1
herbgriffin
17
0

Homework Statement


given input as 100mV peak and expected output to be 10Vpeakto peak...i am having trouble on how to find the different values , like resistors , capacitors ...i am planning to use fixed bias circuit (common emitter configuration) and my transistor gives a value of hfe= min(40) max(150) ,Vce=10V and Ic=150mA...


Homework Equations


Ib=(Vcc-Vbe)/(Rb)
Ic=beta(Ib)
Vce= Vcc-IcRc
Vce=Vc-Ve


The Attempt at a Solution


i solve for the value of hfe using geometric mean square root of (40*150) = 69
and voltage gain to be 50
 
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  • #2
Do you know the input and output impedances to your amplifier?

Using the geometric mean for hfe is not a good idea. Transistors significantly below that value won't have enough gain and one significantly above that value may clip the output. The usual solution is to reduce the range of the transistor gains with negative feedback.

Do you know how to introduce negative feedback in an amplifier? Can you suggest a method for doing that?
 

1. What is a BJT amplifier?

A BJT (Bipolar Junction Transistor) amplifier is an electronic circuit that uses transistors to amplify weak signals. It is commonly used in audio amplifiers, radio frequency amplifiers, and other electronic devices.

2. How does a BJT amplifier work?

A BJT amplifier works by using the transistor's ability to control the flow of current. The input signal is applied to the base of the transistor, which then controls the flow of current from the collector to the emitter. This results in an amplified output signal.

3. What are the different types of BJT amplifiers?

There are three main types of BJT amplifiers: common emitter, common base, and common collector. Each type has different characteristics and is suitable for different applications.

4. How do I choose the right BJT for my amplifier design?

Choosing the right BJT for your amplifier design depends on several factors such as the desired gain, frequency range, and power handling capabilities. It is important to consult datasheets and consider the specific requirements of your design before selecting a BJT.

5. What are some common design considerations for BJT amplifiers?

Some common design considerations for BJT amplifiers include biasing, stability, and thermal considerations. It is important to properly bias the transistor to ensure optimal performance and stability. Additionally, thermal considerations are important to prevent overheating and ensure the reliability of the amplifier.

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