Class A amplifiers formulae help

• shaiqbashir
In summary, the conversation discusses a question about a single stage class A amplifier and its various power calculations. The speaker is unsure of how to calculate certain quantities without a schematic and requests clarification. The conversation ends with a discussion about the concept of "wasted" power in the amplifier.
shaiqbashir
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!

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.

1. What is the formula for calculating the gain of a Class A amplifier?

The formula for calculating the gain of a Class A amplifier is Av = RL / R1, where Av is the voltage gain, RL is the load resistance, and R1 is the input resistance of the amplifier.

2. How do I calculate the power output of a Class A amplifier?

To calculate the power output of a Class A amplifier, you can use the formula P = V^2 / RL, where P is the power output, V is the output voltage, and RL is the load resistance.

3. What is the formula for determining the efficiency of a Class A amplifier?

The formula for determining the efficiency of a Class A amplifier is η = Pout / PDC, where η is the efficiency, Pout is the power output, and PDC is the DC power input to the amplifier.

4. How do I calculate the input bias current for a Class A amplifier?

The formula for calculating the input bias current for a Class A amplifier is Ib = VBE / R1, where Ib is the input bias current, VBE is the base-emitter voltage, and R1 is the input resistance.

5. Can you provide an example calculation for a Class A amplifier?

Sure, let's say we have a Class A amplifier with an input resistance of 10kΩ and a load resistance of 1kΩ. The input bias current is 0.1mA and the output voltage is 10V. Using the formula for gain (Av = RL / R1), we can calculate that the voltage gain is 0.1. To determine the power output, we can use the formula P = V^2 / RL, which gives us a power output of 100mW. Finally, to calculate the efficiency, we use the formula η = Pout / PDC, where PDC is equal to the input bias current (0.1mA) multiplied by the input voltage (10V), resulting in an efficiency of 1%.

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