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- Dec 18, 2013
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Why don't you have a look and you tell me what you think might work. Download LT Spice and copy my diagram and have a go yourself. It's more fun that way.
Adam
Adam
Why not using a simple allpass stage (one opamp only) with a phase shift of -60deg (identical to +120deg) ?
https://en.wikipedia.org/wiki/All-pass_filter
For 50 Hz, almost any opamp will work.
ak
Why not using a simple allpass stage (one opamp only) with a phase shift of -60deg (identical to +120deg) ?
https://en.wikipedia.org/wiki/All-pass_filter
The circuit with three equal resistors R is given in the wiki reference.that's a good ideia, can you show me how I can scale the R and C for a phase shift 120º please?
The circuit with three equal resistors R is given in the wiki reference.
The transfer function is H(s)=(1-sT)/(1+sT) with T=RC.
And the phase is phi=- 2*arctan(2*Pi*f*T).
Hence, for any fixed frequency the value of T can be found for a desired phase phi. Note that -60deg is equivalent to +120deg.
Phi = tan^-1(XC/R) or Phi = 360*fo*dt. But this will only get you close, you will have to adjust the resistor values to get it right. When I did the calculations the circuit didn't produce the desired phase shift so I had to manually change them to get it right, you will need to adjust the values yourself.
Adam
It was something I thought would work just of the top of my head. I don't have anything written down. The formula I gave was to calculate the phase shift. Show us what you did and what was wrong.
Adam
It was something I thought would work just of the top of my head. I don't have anything written down. The formula I gave was to calculate the phase shift. Show us what you did and what was wrong.
Adam
With what? I thought you had it all sorted sorry. Please explain in detail what you are still having issues with.Need help please Arouse1973
With what? I thought you had it all sorted sorry. Please explain in detail what you are still having issues with.
Adam
Here is my offering for calculating the capacitor value for approx. 60 degrees phase shift. Hopefully you can see how this works. This is an example only, you need to input your own values if different.
Thanks
Adam
View attachment 25351
I will try this equations but in this shematic that you posted here each ampop offer 60º degrees phase shift, right?
You said you wanted to know how to work out the capacitor value. I gave you an example. You do realise you can't get 120 degrees from one RC network, you have to add more than one. So you make two 60 degree stages and put them together.
Adam