3 phase oscilator trouble

LvW

Joined Jun 13, 2013
881
Hi people,

I just built this 3 phase oscilator, I've seen a few versions of this online so I thought it'd be good. But I don't get a sine output, it's more of a saw tooth with dead time.
It is a kind of "ring oscillator" - and you cannot expect a "pure" sinewave - unless you are using an amplitude control mechanism (for keeping the level of the created signal within the "quasi-linear" region).
 

ericgibbs

Joined Jan 29, 2010
8,887
hi 1293,
This change to the feedback line and R/C timing will give a close approx to a sine wave.
Obviously the frequency is changed from from the original circuit, but if you want a general purpose sine wave signal it should be OK.
I would add a buffer stage at the output.
E
AAA 056 08.57.gif
 

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ericgibbs

Joined Jan 29, 2010
8,887
hi 1293,
This is @bertus circuit in LTSpice, please check for any build errors as I cannot get it to run, the .IC is required sometimes in LTS to kick start an oscillator.
Lets know what you find.
Attached the LTS asc file.

Eric

AAA 057 09.58.gif
 

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LvW

Joined Jun 13, 2013
881
The reqired gain is "-8" and is fulfilled with the ratio 1500/180=8.333.
However, the last RC stage is loaded with 180kohms.....what about a buffer between?
 

ericgibbs

Joined Jan 29, 2010
8,887
hi @bertus,
Read your PDF circuit for that App, I don't see any errors in my LTS circuit build.?
Will try to find why the LTS version doesn't work, let you know if I get a result.

I have posted the LTS asc file so that the TS can compare result.

E
 

Thread Starter

razorrick1293

Joined Apr 8, 2018
5
i probably should have stated, is there any way to make that latest circuit adjustable in frequency? originally with the ring oscilator i was going to use opto couplers to change the resistance but with feedback in the opamp oscilator it doesnt look possible
 

Danko

Joined Nov 22, 2017
828
i probably should have stated, is there any way to make that latest circuit adjustable in frequency? originally with the ring oscilator i was going to use opto couplers to change the resistance but with feedback in the opamp oscilator it doesnt look possible
Here is 58 Hz oscillator. In some range frequency can be changed by values of capacitors C4, C5, C6 and resistors R1, R3, R5.
C1, C2, C3 are coupling capacitors.
BTW, it is better for you, to tell us maximum information about your project.
What is minimal and maximal frequencies you going to control?

1574440654525.png
 

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Last edited:

Ylli

Joined Nov 13, 2015
799
Easiest/cheapest solution might just be a rotary converter. A DC motor connected to a three phase alternator.
Or you could go with a VFD motor drive, but that would be quite a bit more involved and expensive.
 

KL7AJ

Joined Nov 4, 2008
2,223
The LTspice simulation of this circuit is below and it seems this does not produce a sinewave.
View attachment 192054
I suspect that since all your stages are DC coupled, any small error in biasing will be propagated. Try isolating each stage with a large capacitor (large enough to not affect the phase shift) and see if you can get closer to sine waves.
 
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