# 1 Phase to 3 Phase

Discussion in 'The Projects Forum' started by elektro1, Sep 15, 2009.

1. ### elektro1 Thread Starter New Member

Aug 2, 2009
6
0
Hi there

I've built phase shift oscillator to produce 10V p-p
Now I want to convert from 1 Phase to 3 Phase...

I did think about using RC network to provide phase shift but can't think of
an efficient way, as there will be attenuation due to RC network.

So if any1 can suggest something then it will be great.

Thanks

2. ### JDT Well-Known Member

Feb 12, 2009
658
85
Please post the circuit diagram of your phase-shift oscillator. You may find that an approximate 3 phases already exist.

What is this 3-phase output going to be used for?

How accurate do you need the phases (how close to 120 degrees)?

How accurate and stable do you need the amplitude and frequency?

3. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
Al Dutcher contributed a ring oscillator 3-phase VCO design to EDN awhile back. It uses unbuffered TTL inverter IC's. You might find it helpful to look at.
It starts on page 4 of this PDF:
http://www.edn.com/contents/images/80201di.pdf

Output from each stage is only 600mV p-p, but it's an interesting design.

4. ### elektro1 Thread Starter New Member

Aug 2, 2009
6
0
Well I have got simple phase shift oscillator that uses Inv amp and 3 cascaded RC filter to provide sine-wave. Frequency is 50Hz.
I'm just building a 3phase inverter for simple use in labs to show students how 3 phase works.
If I can get close to 120 degrees that will be good.
It will be good if I can produce phase shift using op-amps as that is what I've been using for oscillation and would like to work with op-amps for phase sift too.

thanks

5. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
Why don't you post your schematic so that we can see what you have so far? A single schematic tells a thousand words.

If you just have a single amplifier, then the intermediate stages of the cascaded RC filters won't be an even 120 degrees.

In the meantime, have a look at Al Dutcher's ring oscillator and the accompanying write-up. It's simple, and produces a pretty nice 3-phase output considering the low parts count and low cost.