what is that Filter Circuit name ?

[mbyka]

Hello friends,
what is the name in the literature of the filter circuit made using opamp that you see in this diagram?
Does anyone have knowledge about it?

CT mean is Current transformer for AC

[especialista]

It seems an "improved" version of the Gyrator Circuit Filter, using OpAmp.

https://en.wikipedia.org/wiki/Gyrator

A gyrator is a passive, linear, lossless, two-port electrical network element proposed in 1948 by Bernard D. H. Tellegen as a hypothetical fifth linear element after the resistor, capacitor, inductor and ideal transformer.[1] Unlike the four conventional elements, the gyrator is non-reciprocal. Gyrators permit network realizations of two-(or-more)-port devices which cannot be realized with just the four conventional elements. In particular, gyrators make possible network realizations of isolators and circulators.[2] Gyrators do not however change the range of one-port devices that can be realized. Although the gyrator was conceived as a fifth linear element, its adoption makes both the ideal transformer and either the capacitor or inductor redundant. Thus the number of necessary linear elements is in fact reduced to three. Circuits that function as gyrators can be built with transistors and op-amps using feedback.

[PM3295]

I don't know how this circuit connects up to the CT.

Normally something like the circuit below will be used with a CT. Basically a differential input op-amp with some LF cutoff. The turn's ratio of a CT is usually quite large (1:100 or 1:1000) to reduce insertion loss. For this reason, you need a burden resistor (R1) to terminate the secondary winding.

The value of C2 and C3 at 100 pF seems low for normal mains current measurement. Higher values in the range of 10-20 nF will do a better job of filtering.

[Sideshow Bob]

R2 and C3 in this configuration do form a fist order low pass filter with a cutoff about 132Khz. But it is not uncommon to place a small capacitor like C3 in an inverting OP-amp configuration as a mean to stabilize the circuit. As the circuit seems to have a roll-off before 132Khz.
@PM3295 Your simulation do not give much of a clue. You need to simulate way past the -3Db point. And also remember to take the GBW product of the opamp into consideration. A first order filter will have -20Db dampening pr decade. A second order filter 40Db and so on

[PM3295]

@PM3295 Your simulation do not give much of a clue. You need to simulate way past the -3Db point.

I didn't need to, as the cutoff obviously is way to high to be used for AC mains frequencies. There is no need to have a cutoff beyond the fifth harmonic of the AC frequency, to get an accurate measurement. The higher cutoff would make sense when monitoring the current in a PWM type switching circuit. I assumed that the AC mentioned refer to AC sinusoidal current.

[mbyka]

guys thankyou for your reply
i just wanted learn the name of this kind lifter by opamp
especialista  answered  it looks improved gyrator

if you have another ideaaboutname of this circuit coulyou write please.

[PM3295]

Any basic electronic book will tell you it is a differential amplifier (suppresses common mode signals), with capacitance added across the two feedback resistors (R2, R3) to roll-off the gain with increased frequency.
 

R2 and C3 in this configuration do form a fist order low pass filter..

It is commonly used in current sensing circuits.

[Sideshow Bob]

Any basic electronic book will tell you it is a differential amplifier (suppresses common mode signals), with capacitance added across the two feedback resistors (R2, R3) to roll-off the gain with increased frequency.
 
It is commonly used in current sensing circuits.

It is a very basic differential amplifier. if you take away the caps. The problem with it is the relatively low Z input impedance. Also Add a few caps and you will have a high frequency roll-off. The heart of most current sensing applications is a some sort of differential amplifier

[PM3295]

The problem with it is the relatively low Z input impedance.

Also the input impedance on the inverting input is only about 1/3 of the impedance on the non-inverting input.

[mbyka]

Any basic electronic book will tell you it is a differential amplifier (suppresses common mode signals), with capacitance added across the two feedback resistors (R2, R3) to roll-off the gain with increased frequency.
 
It is commonly used in current sensing circuits.

yesi i can see  it is a differential amplifier[using by opmap
i am asking  what is the name of this kind filter circuit in  the literature
if you dont know the name  please dont add no necessasry any info(i dont need what is your level about electronic!!)

do it like me 
If you don't know, ask someone who knows


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sallen high pas

[Sideshow Bob]

@mbyka Sorry if I am blunt but I found your post borderline rude and exacting in one's demands. If you look at first post from PM3295 you will find a big clue in what kind of filter it is. He has even spelled it out

Any basic electronic book will tell you it is a differential amplifier (suppresses common mode signals), with capacitance added across the two feedback resistors (R2, R3) to roll-off the gain with increased frequency.

And I also did give a big hint here

R2 and C3 in this configuration do form a fist order low pass filter with a cutoff about 132Khz. But it is not uncommon to place a small capacitor like C3 in an inverting OP-amp configuration as a mean to stabilize the circuit. As the circuit seems to have a roll-off before 132Khz.
@PM3295 Your simulation do not give much of a clue. You need to simulate way past the -3Db point. And also remember to take the GBW product of the opamp into consideration. A first order filter will have -20Db dampening pr decade. A second order filter 40Db and so on

I post a link for you. And wish you the best of luck. We are here to give you a nudge in the correct direction. Not to educate you. Bye!

[PM3295]

yesi i can see  it is a differential amplifier[using by opmap
i am asking  what is the name of this kind filter circuit in  the literature
if you dont know the name  please dont add no necessasry any info(i dont need what is your level about electronic!!)

Please try connect the dots...
Differential opamp + roll-off at 20 dB per decade (think type of filter that do this) = Differential_(?PF)