I did something similar to this a while back to power an old military
artificial horizon. I don't think I ever actually drew out a schematic - too
simple; I just wired it up on a perf board.

Vcc was 5 volts, regulated by a 7805, from 12 volts in my case, but 24 volts
should work too. I used a 555 to generate the clock, which was 400 Hz *
9=3600 Hz. That clock was fed to a 4 bit counter. The output of that counter
was fed to the input lines of a 74154 decoder.


http://www.datasheet.in/datasheet-ht...uctor.pdf.html
http://www.datasheet.in/datasheet-ht...ilips.pdf.html
http://www.datasheet.in/datasheet-ht...ments.pdf.html
http://www.datasheet.in/datasheet-ht...uctor.pdf.html



On the output side of the decoder, 3 bits each were used for each phase.
Phase A was y0, y1 and y2 fed through 1n914 diodes as a "wired or" circuit.
Phase B was y3, y4, and y5. Phase C was y6, y7 and y8. Y9 went to reset on
the counter.

Now we have 3 phases of square waves at 5 volts. feed those phases backwards
through 3 small 120v to 5v transformers. Total cost - $10 or so at Radio
Shack.

The fact that they are square waves, not sine waves has no effect at all as
far as I could see. You are just running a tiny 3 phase synchronous motor.

3 phase, 400 cycle military instruments are super cheap on ebay. You can
mostly set up a complete IFR panel for really cheap!





"karel" wrote in message
...

"Robert Bonomi" wrote in message
...
In article . com,
wrote:
I've got an ARU 44 gyro and I'd like to power it off my 24VDC system.
It needs 115VAC 3 phase, and about 75W to 100W. Is there an off the
shelf unit that can do this, or maybe someone knows of a schematic to
build my own? I'm an electronics engineer so I can do this, but
inverters are not my specialty so any guidance would be greatly
appreciated.


WAG says it's probably 400 cycle, as well. not 60Hz.

Design can be fairly simple, particularly if you use a micro-controller
for the 'logic' of phase generation.

start with a clock that is 2 X phases X frequency,
Feed it into a counter, that counts from 0 to (phases-1).
Hang a number of comparators on the counter outputs, one that
triggers for each value.
Send each comparator output through a flip-flop.
(this gives you a 50% duty-cycle output for each phase,
and at the right frequency.)

[now for the "analog stuff

low-pass filter to sine-wave.

Amplify to get the needed voltage/current levels.

Voila!

And how does this manage to produce 110 volts from 24?
Some kind of transformer wil be required.
Step-up rectifying might be an option
but will be hard at these power levels,
i.e. require huge condensers.

But I'm afraid I am no more able than you
to really fill O/P's request for a schematic

PS does anyone know how important the true
sine wave is for this kind of equipment?