3 phase from func.gen. IC

I would look at Microchip's application notes. I think they have a PIC that is used for variable frequency drives. Does the whole thing. The function generator with three phase output. Might not be what you want as the sinewave would not be a real sine wave. It would be a pulse width modulated output.

=20 Dan

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View in Courier:


CLK>-+--[COUNT]-+-[LUT000]--[DAC]--[LPF]-->
                |
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                +-[LUT120]--[DAC]--[LPF]-->
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                +-[LUT240]--[DAC]--[LPF]-->


JF

How about this:

Given a single-phase sine wave as input, you could make an all-pass network that would give two outputs that are 90 degree phase shifted at all frequencies, then do some analog summing to make 120 and 240. There are some allpass phase shifter circuits used in ham-radio type SSB transmitters that aren't too horrible.

It could also be done with an integrator to make a 90 degree shift, some sort of AGC to restore the amplitude, and some analog mixing.

And a few other terrible ways.

But it's probably easier to build a generator that inherently makes quadrature or 3-phase sine waves.

John

Analog Devices do multi-output DDS chips that would probably do the job.

A quick look suggests that a pair of synchronised AD9958 chips would do the job

8/products/product.html

but a bit of trigometry with an AD9854 - which nominally generates pairs of outputs in quadrature - might do the job for less money.

-- Bill Sloman, Nijmegen

No one's answered your question yet.

Phase lock two function generators together, 90 degrees apart, and use resistor networks to generate the +120 and -120 degree shifted sines. This assumes that you can make one of them the slave.

Or if you must have three individual signals (maybe you want one sine, one triangle, and one square?), then phase lock two generators to the one, with appropriate phase offset.

But I think most folks feel you asked the wrong question...

Had you asked "3 phase from some collection of integrated circuits" then most of the other answers you've gotten would be better: make something up. Either make it digital, using a DDS chip if you need signals up to the MHz range, or using a microcontroller if you just need signals up through the audio.

Or make it analog, with a three-stage circuit that produces a 120 degree lag (or an inversion and a 60 degree lag) at each stage, with some sort of AGC on at least one stage and all three stage's frequency-determining components ganged.

Or make a two-stage circuit with 90 degrees shift in each stage and an overall 180 degree inversion. I'll bet that with care and some thinking you could come up with a Wien bridge circuit that'd put out pair of signals in quadrature at the same amplitude, then you could use your resistor network to get your three phases.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

The only easy way uses four function generator ICs. Run one at

6x the frequency you want (easy, just select a smaller integrator capacitor), and divide down its square wave with three stages of twisted-ring-counter connected flip/flops. That gives you three accurate phases of square waves, and an approximate current-program source to run the slaves.

Then using the same control current for the three slave generators, phase or pulse-lock them each to one of the square wave phases. Injecting an error signal current into pin 7 of XR2206 would be a typical ploy. XOR gates and RC filters are adequate phase comparators for the square wave outputs of generators.

Learn to code a uC chip... A Pic, AVR, ATEML, ARm etc.. that has at least 3 ADC outputs.. The smaller family chips use a PWM (Pulse width modulator) that can form a Sin wave on the output..

You code the math to generate the first base sine and then, offset the other outputs at the proper angle.

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That doesn't supply the OP's request for something which will generate
two sine waves displaced from a driving sine wave by +/- 120 degrees.

It does, however, provide a way to generate three sine waves displaced
from each other by 120 degrees which is way more complex than the way I
posted.

 
JF

Refer to analog computers and work done then (40 or so years ago well before "solid state"). Even the x=-x.. generator needs tuning for sine generation, so what is wrong with using three phase retard stages with "ganged" tuning to maintain fixed phase delay on each stage?

DIY; use a look-up table containing a DAC representation of a sine wave and have the program "pick off" (pun NOT intended) the phases for output to 3 DACs.

If i played a fLUTe,would that do?

ADC outputs? Do you mean DAC?

He never knows what he means.

--
Greed is the root of all eBay.

sin(x + y) =3D sin x. cos y + cos x.sin y

sin(2.pi.t + 3.pi/2) =3D sin(2.pi.t).cos(2.pi/3) + cos(2.pi.t). sin(2.pi/3)

=3D sin(2.pi.t).-0.5 + cos(2.pi.t). 0.866025403

which you can get with a summing amplifier, as you can with sin(2.pi.t

• 4.pi/3)

-- Bill Sloman, Nijmegen

Once you've got two sine waves in quadrature, getting three phase is simple. Just use a Scott-T transformer. These were once use for power applications, but since two phase power is almost extinct, they are now used for connecting servos that use synchros to those with resolvers.

--
Virg Wall, P.E.

Yes, of course ;)

I think you should be the last one, commenting on that.

When did you start thinking?

--
Lead free solder is Belgium's version of 'Hold my beer and watch this!'