Help to solve Operational amplifier

[kamikaze1993]

Hello, I just wondering if anyone could help me solve this tasks?

Task1: Max theoretical effect ?

Task2: What is the biggest value v4 may have before output signal is inverted?

Task 3: How big is the input impedance?

Task4: How big is the lower branch value?

Task5: How big is the upper branch value?

 

[LvW]

With the exception of task 4 I do not understand any of the other tasks.
It seems necessary to have some additional explanations.

 

[ramussons]

Frankly, I'm not able to figure out what is being asked for except Task 3.
C5, R8, R5, C2 form a Bandpass Filter.
U2 with R7, R6 and C1 is an active High Pass Filter with around 5Hz cutoff decided by R6 C1.

 

[kamikaze1993]

We assume that the operational amplifier is ideal. Circuit Is an audio power amplifier to drive a speaker at 8 ohms. The sound source is operated as sine generator v4, and operational amplifier supplied +10 V and -10 V. What is the maximum theoretical power amplifier can give out in an 8 ohm speaker when the sound source (v4) sinusoidal voltage source, which is adjusted to the max amplitude until the output voltage "cut" , with a frequency of 1 kHz.


Does the task now, give more sense?

 

[ramussons]

We assume that the operational amplifier is ideal. Circuit Is an audio power amplifier to drive a speaker at 8 ohms. The sound source is operated as sine generator v4, and operational amplifier supplied +10 V and -10 V. What is the maximum theoretical power amplifier can give out in an 8 ohm speaker when the sound source (v4) sinusoidal voltage source, which is adjusted to the max amplitude until the output voltage "cut" , with a frequency of 1 kHz.


Does the task now, give more sense?

An ideal Op Amp will give a max swing of 10 Volts, so it can deliver 10^2 / 8 = 12.5 Watts RMS.

I could not understand this part in your post.

 

[kamikaze1993]

The amplitude v4 adjusted to the max, before the output voltage is "cut". f = 1 kHz.

 

[BobK]

An ideal Op Amp will give a max swing of 10 Volts, so it can deliver 10^2 / 8 = 12.5 Watts RMS.

I could not understand this part in your post.

You have computed the power in a square wave. For the RMS power of a sine wave, divide the voltage by sqrt(2) which divides the power by 2.

6.25W

Bob

 

[kamikaze1993]

We assume that the operational amplifier is ideal. Circuit Is an audio power amplifier to drive a speaker at 8 ohms. The sound source is operated as sine generator v4, and operational amplifier supplied +10 V and -10 V. What is the maximum theoretical power amplifier can give out in an 8 ohm speaker when the sound source (v4) sinusoidal voltage source.The amplitude v4 adjusted to the max, before the output voltage is "cut". f = 1 kHz.


Task1: Max theoretical effect ?(answer by Bob = 6,25 W)

Task2: What is the biggest amplitude sine source v4 may have before the output signal is distorted?

Task 3: How big is the impedance of the amplifier, as seen from the source when f = 1 kHz?

Task4: How big is the lower boundary value?

Task5: How big is the upper boundary value?


Are the for reaming task easier too understand now?

 

[AnalogKid]

Easier for me, but what about you? What work have you done to answer these questions? You used the term "ideal" to describe the opamp as a way to qualify the questions, so you must know what it means What are the essential characteristics of an ideal opamp, and how do they apply to your questions?

Task 3 hint: What are the impedances of C5 and C2 at 1.0 kHz?

Task 2: First you said inverted, then you said distorted. Both are possible. Why?

ak

 

[kamikaze1993]

Task3 : c2: 2*pi*1000*1,5*10^-9

c5: 2*pi*1000*0,47*10^-6

Would this be the answer to the input impedance?




Task2: I don't seem way it is possible that op-amp could be disorted and inverted, can you explain this further?

 

[BobK]

For an ideal op amp:

Distorted: The output signal is larger than the supply voltage.
Inverted: This can happen on real op amps, but not on an ideal op amp.

Bob

 

[kamikaze1993]

thank you Bob, but anyhow I do not understand how to solve the task 2,3,4 and 5? Someone who is able to guide me through the tasks?

 

[AnalogKid]

Task 2: The output voltage equals the input voltage times the gain of the amplifier circuit. Since you know the maximum output before distortion, you can divide that value by the gain of the amplifier to find the equivalent input voltage.

ak

 

[kamikaze1993]

Ak, so the answer too task to would be 6,25 W / 10 V ?

In task 3 would the impedance be like this?

c2: 1/2*pi*1000*1,5*10^-9

c5: 1/2*pi*1000*0,47*10^-6

 

[AnalogKid]

Ak, so the answer too task to would be 6,25 W / 10 V ?

No.

What is the maximum output before distortion?

 

[kamikaze1993]

Is the maximum output 0,1V?

 

[AnalogKid]

In post #4 you said to assume the opamp was ideal. What are the characteristics of an ideal opamp?

 

[kamikaze1993]

"Output signal is larger than supply voltage". Do I need the current to solve task 2? Or do I need some other information before i solve it?

 

[AnalogKid]

That is incorrect. This is not a power supply. The output signal cannot be greater than the ssupply voltge. Is this homework or school related?

 

[kamikaze1993]

This is an old exam without solutions. Ak could you explain how solve this problem? I've seen in my formula book and have tried for a long time too solve this tasks. I have seen through lecture notes and search on the web.