3 phase from func.gen. IC

Wed Mar 10, 2010 11:52 am   

What would be the simplest way to derive a simultaneous three phase
output from a sine wave produced by a single function generator IC ...
that does not change as the frequency is varied?

Specifically, two additional sinewaves remaining 120 and 240 degrees
out of phase with the original as the frequency is varied between
100Hz and 1KHz.

Kevin Lang

Wed Mar 10, 2010 2:08 pm   

On Mar 10, 10:52 am, kevinl...@hartley.com (Kevin Lang) wrote:

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.


Dan

Wed Mar 10, 2010 2:53 pm   

On Wed, 10 Mar 2010 10:52:55 GMT, kevinlang_at_hartley.com (Kevin Lang)
wrote:


---
View in Courier:


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


JF

Wed Mar 10, 2010 5:38 pm   

Kevin Lang wrote:

How about this:
http://www.techbriefs.com/content/view/1839/32/

Wed Mar 10, 2010 5:42 pm   

On Wed, 10 Mar 2010 10:52:55 GMT, kevinlang_at_hartley.com (Kevin Lang)
wrote:


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

Wed Mar 10, 2010 6:19 pm   

Kevin Lang wrote:

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

Wed Mar 10, 2010 7:17 pm   

On Mar 10, 5:42 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

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

http://www.analog.com/en/rfif-components/direct-digital-synthesis-dds/ad9958/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

Wed Mar 10, 2010 11:00 pm   

On Mar 10, 2:52 am, kevinl...@hartley.com (Kevin Lang) wrote:

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.

Thu Mar 11, 2010 1:33 am   

Kevin Lang wrote:


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.

Thu Mar 11, 2010 2:44 am   

On Wed, 10 Mar 2010 21:56:59 +0530, "pimpom" <pimpom_at_invalid.invalid>
wrote:


---
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

Thu Mar 11, 2010 6:58 am   

Kevin Lang wrote:

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?

Thu Mar 11, 2010 7:01 am   

dcaster_at_krl.org wrote:

wave and have the program "pick off" (pun NOT intended) the phases for
output to 3 DACs.

Thu Mar 11, 2010 7:02 am   

John Fields wrote:

Thu Mar 11, 2010 11:27 am   

On Wed, 10 Mar 2010 19:33:19 -0500 Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa__at_charter.net> wrote in Message id:
<0AWln.78156$K81.64778_at_newsfe18.iad>:


ADC outputs? Do you mean DAC?

Thu Mar 11, 2010 4:43 pm   

JW wrote:


He never knows what he means.


--
Greed is the root of all eBay.