whats is the gain of this ckt ??

[aamir1]

View attachment 60730

 

[bountyhunter]

It's a resistive divider followed by a buffer. I think you should be able to do this one.

 

[Roff]

Is this a trick question? The output waveform will be clipped.

 

[bountyhunter]

Is this a trick question? The output waveform will be clipped.

I don't think so. The DC voltage source will look like a virtual ground to AC signal so the resistive divider will be in effect.

I don't want to give the whole thing away, but I don't think the output will be near clipping.

 

[duffy]

aamir - the common term for that circuit is a "Unity Gain Amplifier".

 

[MrAl]

Hi,


This circuit requires a little more careful consideration because of the way it is biased and because of the rather large input voltage and because a non rail to rail op amp is being used.

Although the op amp is being used as a unity gain amplifier, the gain of this circuit is not 1. That's because the two resistors (even though one is to a DC source) form a resistive voltage divider that divides the input by 2 [hint hint ]

Unfortunately, the output of the LM358 can not reach up to +20v with only a +20v supply voltage, so this circuit will clip the upper peaks of the output to about +18.5 volts. The lower peaks would probably experience just a tiny tiny bit of clipping because the LM358 output can reach almost all the way to ground, which may be acceptable in some applications. It's doubtful whether or not the upper peak clipping could be tolerated however in most applications.

As a side note, with the 10uf capacitor shorted the circuit could actually work if there was a negative supply voltage present too, because the bias voltage would then get divided by 2 also.

 

[audioguru]

Above about 2kHz the output will become a ramping triangle waveform and its output level decreases when the frequency increases because the LM358 has a very low slew rate.

 

[Roff]

I don't think so. The DC voltage source will look like a virtual ground to AC signal so the resistive divider will be in effect.

I don't want to give the whole thing away, but I don't think the output will be near clipping.

The voltage at pin 3 will swing from 0V to +20V. Think again.

EDIT: Perhaps you misread the input signal as 20V peak-to-peak?

 

[MrAl]

Hi,

I agree, in part. In part because the output will never make it to +20v because the LM358 will clip at about Vcc-1.5v, which in this circuit is around 18.5 volts.
With the cap shorted though it would only reach to +15v, but then of course the negative peaks would be clipped severely.

 

[bountyhunter]

I did interpret the original circuit to mean 20V maximum AC amplitude, so it will clip if it is actually 40 V total peak to peak. Kind of a stupid problem. And as already pointed out above, it will probably distort the sine wave due to slew rate limiting.