# Phase Shift Oscillator

Discussion in 'General Electronics Chat' started by traitorousdevil, May 29, 2010.

1. ### traitorousdevil Thread Starter New Member

May 24, 2010
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Hi...
According to the attachment, I'm wondering... If I would just want the phase to be shifted 120 degree only, is it that possible with I'm using 2 pair of RC?

If it is possible, what will be the value of both pair of RC pair? Is that can be calculate through any calculation or...? The output frequency I wish to get is just 50Hz which is similar with my input frequency as well...

Thanks... =)

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2. ### SgtWookie Expert

Jul 17, 2007
22,198
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Jim,
You seem to be working pretty hard on this.

What's your ultimate goal? A 3-phase output?

It would help us a lot to help you more quickly if we know for sure what you need.

Phase shifting by a given amount of degrees is usually easier if it's done in a loop.

3. ### traitorousdevil Thread Starter New Member

May 24, 2010
15
0
Yupz... The 3 phase output with each 120 degree phase shift...
I'm trying combining 3 phase shift oscillator to convert the single phase to 3 phase... Although I'm not sure would it work... =P

I have a confusion here... Where is the input for the oscillator in previous post's attachment? I have been searching lots of phase shift oscillator circuit but none of them shown the position of input signal should be...

4. ### traitorousdevil Thread Starter New Member

May 24, 2010
15
0
I have done my circuit~! But there's some problem...
As shown in attachment, my output voltage is damn low... what changes can i make 2 increase the output voltage... Also, the 3 output have different voltage... Any ways to make 3 of them have similar voltage range? * 0v-20V

Next, that's the problem for my 3rd output... Why is my output like being clamp and move up apart from the previous? Arghhh~! How I'm gonna fix it?

Lastly, how do i count whether my output waveform is that 120 degree? =P

Thanks...

**Hope the attachment is clear enough for you guys... =)

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Mar 6, 2008
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6. ### Audioguru Expert

Dec 20, 2007
10,725
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An oscillator starts oscillating from the noise in its components being amplified.
An oscillator does not have an input signal.

The first phase-shift oscillator needs a voltage gain of about 29 or 30 from its transistor.

7. ### anany387 New Member

Feb 23, 2014
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i also want to make this project of single phase to 3 phase conversion for operating a three phase motor...plzz help me...send details to anany387@gmail.com....i will be highly obliged..regards

8. ### crutschow Expert

Mar 14, 2008
20,826
5,920
Here's a circuit to generate the second and third phase from a single phase signal using op amp all-pass filters. All-pass filters have a constant amplitude with frequency but can change the signal phase anywhere from 0 to plus 180° (capacitor in series) or minus 180° (capacitor to ground). The RC values to give 120° and 240° are shown for a 400Hz signal but you can adjust them for any frequency you need. For 50Hz, increase the RC time-constants by a factor of 8.

Nov 4, 2013
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10. ### LvW Well-Known Member

Jun 13, 2013
769
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As already mentioned: An oscillator has no signal input. It creates the signal by self-excitation.

As to the three-phase oscillator: For my opinion, a modified BUBBA oscillator (to be found via google) with three instead of four passive RC sections would be a good, simple and reliable solution.

May 11, 2009
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12. ### tcmtech Distinguished Member

Nov 4, 2013
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but post #7 came in today so I answered todays question.

13. ### LvW Well-Known Member

Jun 13, 2013
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Wow - I didn`t notice.