3phase sine wave generator

Thread Starter

jayanthyk192

Joined Jan 23, 2010
80
hi,
i'm trying to build a 3 phase sine wave generator.i found one on google.(file attached).can anyone briefly explain the circuit or give a link where i can study about them.can anyone tell me how to change the frequency of the waves.all i could understand was,at each opamp the sine wave gets a phase change of 120 degrees from the original.i could'nt figure out how the first sine wave is generated.

please help.

please give me a better circuit if any.

thank you.
 

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SgtWookie

Joined Jul 17, 2007
22,227
I threw that circuit together a couple of years ago, I think.

It's just a ring oscillator. You can connect any odd number of inverting amplifiers together that have a gain greater than 1, and you wind up with a ring oscillator.

Have a look at the attached .PDF file; scroll down to the 4th page, and read the article entitled "Inverters form three-phase VCO". It's a bit more simple that the circuit you found, and you can control it by controlling the current into the U04 IC.
 

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Thread Starter

jayanthyk192

Joined Jan 23, 2010
80
I threw that circuit together a couple of years ago, I think.

It's just a ring oscillator. You can connect any odd number of inverting amplifiers together that have a gain greater than 1, and you wind up with a ring oscillator.

Have a look at the attached .PDF file; scroll down to the 4th page, and read the article entitled "Inverters form three-phase VCO". It's a bit more simple that the circuit you found, and you can control it by controlling the current into the U04 IC.
yes the circuit was made by you. traced the file and found it the forum itself.:)

i found the datasheet of U04 and found they were 'not gate' IC.but according to the pdf you gave the output is very low.how to increase the voltage?can i be using an L293d,i thought i could'nt because the logive voltage should be higher.

can you please briefly explain the circuit?the explanation in the pdf was a bit complex.
can you please tell me how to increase the freqency in your circuit,because i already built the circuit?

thank you.
 

SgtWookie

Joined Jul 17, 2007
22,227
i found the datasheet of U04 and found they were 'not gate' IC. but according to the pdf you gave the output is very low. how to increase the voltage?
"NOT gate" is a rather archaic term. "Inverter" is preferred.

Yes, the output is rather low. You could use op amps to increase the voltage output in each phase. What op amps to use would depend on what frequency range and voltage you need.

can i be using an L293d,i thought i could'nt because the logive voltage should be higher.
I don't know what you are trying to use an L293D for.

can you please briefly explain the circuit?the explanation in the pdf was a bit complex.
Here's a tutorial on ring oscillators:
http://www.odyseus.nildram.co.uk/RFIC_Circuits_Files/Ring_Oscillator.pdf
Another:
http://www.asic.uwaterloo.ca/files/vcotut.pdf
can you please tell me how to increase the freqency in your circuit,because i already built the circuit?
The LM324 opamp is a very slow opamp. Using real world parts, it will be doing well if it gets to 8kHz. You would have to start off using a much better opamp to obtain higher frequencies.

However, 74ACU04 or 74HCU04 or 74VHCU04 ICs' are really quite inexpensive, and available from multiple suppliers.

Why don't you explain the range of frequencies that you require, and what your output voltage requirements are?
 

kingdano

Joined Apr 14, 2010
377
just to inform the masses:

in college a professor of mine created a 3-phase sine wave signal in an FPGA/CPLD (i forget which).

i have no schematics or anything - but it is possible.
 

Thread Starter

jayanthyk192

Joined Jan 23, 2010
80
"NOT gate" is a rather archaic term. "Inverter" is preferred.


The LM324 opamp is a very slow opamp. Using real world parts, it will be doing well if it gets to 8kHz. You would have to start off using a much better opamp to obtain higher frequencies.

Why don't you explain the range of frequencies that you require, and what your output voltage requirements are?
the output required is 5v.the frequency range that i want is from 0-5/6KHz.i.e i want to tune the frequency from o Hz to 6KHz.

and can you please suggest a method by which i can tell if an output is varying or is it steady.because in your circuit i connected 3 led's without changing frequency and i could'nt see it blink.the output at each phase measured around 3.24(the input voltage i gave was 5V)which is the RMS value of input.i tried connecting a speaker to it but it didn't make any kind of sqealing sound,i thought it made ultrasound.so please suggest a proper method by which i can check if the output is ac or dc.
 

SgtWookie

Joined Jul 17, 2007
22,227
You won't be able to get an oscillator down to 0 Hz, unless you turn the power off.

You are putting too much of a load on the LM324 ring oscillator by using LEDs or a speaker. Also, that circuit as shown was oscillating in the neighborhood of 17kHz, which would be far too fast to see flashing. You would need to use an oscilloscope to see the outputs.
 

SgtWookie

Joined Jul 17, 2007
22,227
What is the range of frequencies that you need to have?

Be realistic.

The narrower the range, the easier the circuit will be to construct.
 

Thread Starter

jayanthyk192

Joined Jan 23, 2010
80
in that case the freq range can be from least to 1KHz or atleast to 500Hz so that i can test my circuit.any range from the least possible to highest possible would be an ideal case.i need the output voltage to be 5V.
 
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Thread Starter

jayanthyk192

Joined Jan 23, 2010
80
in that case the freq range can be from least to 1KHz or atleast to 500Hz so that i can test my circuit.any range from the least possible to highest possible would be an ideal case.i need the output voltage to be 5V.please reply as soon as possible.
 

retched

Joined Dec 5, 2009
5,208
You have to decide. The lowest possible to the highest possible doesn't help.

You say please reply as soon as possible. Reply to what?

YOU have to answer the question first. Its up to you.

When you say things like "Highest possible would be ideal" you are not answering anything.

We can guess at what you want...

here is a .1Hz to 20MHz frequency generator that outputs sine waves and can do square and triangle with a simple switch.

http://www.simplecircuitdiagram.com/2009/06/16/high-frequency-function-generator-using-max038/
 

Thread Starter

jayanthyk192

Joined Jan 23, 2010
80
well this is almost what i wanted.i actually wanted to add a pot in the circuit itself.but this should do.can you plese tell me how to connect the output to the circuit i alredy posted at the beginning of the thread(also attached below)so that i get the 3 phase output i want?
 

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SgtWookie

Joined Jul 17, 2007
22,227
See the attached.

Most values needed to be changed in order to get a halfway decent looking sine wave at the lower frequency.

As shown, the three-phase output will be in the vicinity of 500Hz. To get higher frequencies, decrease C1 through C3. 4.7uF will give you around 900Hz. All three capacitors must have the same value, or you will not get 120° between the phases.

The voltage reference was changed from a pot to a TL431, which is a shunt regulator aka "adjustable Zener". Wired as shown, a TL431 will have a nominal 2.5v from cathode to anode. A 10uF cap is required to keep the TL431 in the stable region.

If you don't happen to have a TL431, you could use a regulator such as an LM317 wired to output 2.5v.

Vcc is 6.5v; this is because the opamp used cannot reach to the positive supply rail, and you need 0v-5v out. This circuit will output from around 100mV to about 4.8v. If you increase Vcc to 6.7v, it should reach 5v with a light load on the output of the opamps.

I don't know what you are planning on driving with this circuit. However, if you put a low-impedance load (below around 10k Ohms) on any of the outputs, it will stop oscillating.

If you want to drive something that has a lower input impedance, you will need to buffer the outputs. You can create a high-impedance voltage follower by using an opamp with it's output wired to the inverting input, and the input signal to the noninverting input. The output will be a mirror of the input signal, but with more current drive capability.
 

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