Class A amplifiers formulae help

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Discussion Overview

The discussion revolves around the calculations related to a single stage Class A amplifier, focusing on various power-related parameters such as DC input power, power loss in the load resistor, AC power across the load, power delivered to the transistor, power wasted in the transistor, and overall efficiency. The scope includes theoretical and mathematical reasoning related to amplifier performance.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • The original poster (OP) provides specific values for Vcc, Vceq, Icq, RL, and Ip, and asks for help in finding several power-related quantities.
  • The OP claims to know how to calculate DC input power and overall efficiency but seeks confirmation and assistance for the remaining calculations.
  • Some participants propose formulas for DC power loss in the load resistor and AC power developed across the load, but the OP expresses uncertainty about the formulas for DC power delivered to the transistor and DC power wasted in the transistor.
  • One participant notes the importance of having a schematic for accurate calculations, as different biasing methods can affect the results.
  • Another participant reflects on the concept of DC power wasted in the transistor, indicating that it can vary with the input signal and is not a straightforward calculation.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the calculations due to the lack of a schematic and differing interpretations of the terms used, particularly regarding power dissipation and efficiency in the context of varying input signals.

Contextual Notes

The discussion highlights limitations such as the absence of a schematic, which may affect the ability to calculate certain parameters accurately. Additionally, the definitions of "wasted" power and efficiency are noted to be context-dependent and not universally agreed upon.

Who May Find This Useful

This discussion may be useful for students or individuals interested in understanding Class A amplifier performance, power calculations, and the implications of different biasing methods on amplifier efficiency.

shaiqbashir
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HI guys!

well! i have got a question with me. Some forumlae i know and some i dont! please help me in solving it.

There is a single stage class A amplifier which has

Vcc =20V
Vceq = 10V
Icq = 600 mA
RL = 16ohms
Ip=300mA.

We have to find:

1) DC Input Power
2) DC Power Loss in load resistor
3) AC power developed across load resistor
4) DC power delivered to the transistor
5) DC power wasted in transistor
6) OVerall efficiency

okz, now i know how to find (1) and (6). What should i do for remaining. Following I am wrtitng what i think about them. Please tell me if I am wrong or correct. If I am wrong then what is the correct formula:

2) P = (Icq^2) RL
3) P=0.5 Icq x Vceq
4) don't know
5) don't know

Please tell me those formulae which i don't know and also make those confirmed which i have written above.

i shall be thankful to u for this act of kindness.

Good Bye!
 
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Do you have a schematic of this amplifier? You can bias up class A amps in different ways to trade off THD versus quiescent power dissipation. Without more info, I don't think you can calculate several of the quantities you are asking for.
 
Well! for the 1st question, i don't have a schematic. i have written that as it came to me. It is just written that it is a single stage class A amplifier. So please be straight forward.
 
shaiqbashir said:
5) DC power wasted in transistor
I remember this as being thought of as the power consumed with no input signal supplied.
This is not a clear concept due to the fact that "wasted" and "efficiency" vary with the input signal.
 

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