I came up with the following circuit for amplifying the output AC sinusiodal signal of the CT. Which has a peak voltage of 15mv 50hz sinewave. Now when I connected the circuit and powered it with 5v I measured the output using a multimeter and I saw that the output was 5v. And when I connected the signal from the CT. Nothing changed. The value remained the same. What is wrong with this?. Could someone please suggest anything?
What's that chopped off on the right-hand side? Do you have the output connected to 5V?
That is connected to the ADC of a microcontroller. The output is not connected to 5v. 
Could the fact that ne5534 is an audio amplifier be a source of the problem?
shivakumarj1995:
Could the fact that ne5534 is an audio amplifier be a source of the problem?
Well you are not powering it correctly. The data sheet says:-
Wide Supply-Voltage Range ±3 V to ±20 V
So that means that 6V is the lowest voltage that it takes to drive correctly and you only have 5V.
The Recommended Operating Conditions is a minimum of +5V and -5V, so you are way off that.
1M/20k = 50
But at higher gain, that configuration is going to become unstable. An attenuator would be better than that particular way of varying the gain.
If you need voltage gain in the range of 100x, it is better to distribute the gain between two Op Amps.
Also, the NE5534 is rated for a minimum of +-3V, at least the On Semiconductor version is. Other manufacturers may have other ratings.
Also, the NE5534 is rated for a minimum of +-3V, at least the On Semiconductor version is.
Yes it says that in the "headline" but it also says:-
The On Semi version says:
Large Supply Voltage Range: +-3.0 to +-20 V
I didn't look at datasheets for any other manufacturers for this. I did say they may be different.
It also says 10Vrms with +-18V supplies, which is going to be only 14Vpk. Leaving very little overhead if running this from merely +-5V supplies.
I'm trying to say that this is a bad choice for this purpose.
Leaving very little overhead if running this from merely +-5V supplies.
Yes but he is not using +-5V, just a single ended 5V so that corresponds to +-2.5V. So he is trying to operate it out of spec.
That bit I posted was from the Ti data sheet.
Use a rail-to-rail opamp from 5V. How are you connecting the current transformer (that circuit appears to be
a slice of a diagram for an electret condenser microphone amplifier).
Does your CT have a built-in burden resistor? What value is it? You'll need to not load down that
burden resistor load significantly or you'll change the output level. Use a non-inverting opamp
circuit to avoid loading the source perhaps?
MarkT:
Use a rail-to-rail opamp from 5V. How are you connecting the current transformer (that circuit appears to be
a slice of a diagram for an electret condenser microphone amplifier).Does your CT have a built-in burden resistor? What value is it? You'll need to not load down that
burden resistor load significantly or you'll change the output level. Use a non-inverting opamp
circuit to avoid loading the source perhaps?
There is a burden resistor of 200ohm parallel to the CT. So you are saying in should use connect the CT output into the non inverting input of the OPAMP? I don't have access to - + dual supplies only a few adaptors. So I will power it with 12v supply and see what it does.
Grumpy_Mike:
Well you are not powering it correctly. The data sheet says:-So that means that 6V is the lowest voltage that it takes to drive correctly and you only have 5V.The Recommended Operating Conditions is a minimum of +5V and -5V, so you are way off that.
I don't have access to a dual supply only a few adapters. So I will power it through a 12 V or 9v supply and see what it does.
It will blow up your Arduino because the output will be over 5V. It needs to be reduced with a potential divider before feeding it into the Arduino.
Why not just get a decent op-amp?
Grumpy_Mike:
It will blow up your Arduino because the output will be over 5V. It needs to be reduced with a potential divider before feeding it into the Arduino.Why not just get a decent op-amp?
Of course I won't be giving any signal more than 5v to the arduino I wanted to atleast amplify the 15mv signal using the OPAMP. I put a 12v supply and the output still is going all the way to the 12v even without any input signal
You need a rail-to-rail opamp, and use the right configuration to amplify the signal without loading it, the
circuit you described has a variable input impedance dependent on the input potentiometer so its not
going to useful for measurement. With 200 ohm burden you should keep the loading impedance well above
that, so 20k or more is good, or else you'll have to compensate for the loading in your calculations - which
requires that impedance to be constant/known, not a potentiometer...
You existing circuit assumes the opamp can operate down to 1/3rd of 5V, 1.7V or so, and the NE5534A
just cannot do that - it can barely get down to 3V, which is why its minimum supply range is 6V. In practice
this chip is used with +/-15V or +/-9V supply in low-noise audio amps and effects units, its not a low-voltage
device, its a low noise device.
Grumpy_Mike:
Yes but he is not using +-5V, just a single ended 5V so that corresponds to +-2.5V. So he is trying to operate it out of spec.
Yes, someone mentioned adding a -5V supply, I was pointing out that even with that, it isn't the best idea.
That bit I posted was from the Ti data sheet.
OK. I specified On Semi and said others may vary.