Oscillator Design in Pspice/ Multisim

[kunene]

Hi friends

I would like your help in designing the circuit attached in Pspice/Multisim.

I have little experience in those softwares, so your help is much appreciated.

If you can draw them and share the file so I can also open in those softwares. thanks in advance.

 

[ericgibbs]

hi,
This is the circuit running in LTspice, it may help you to convert to PSpice.

The trim potentiometers are very sensitive in setting.

 

[kunene]

thank you so much.

I have one question though. Why the choice of potentiometes in the circuit, why not fixed resistor?
any idea of the purpose of the potentiometers in this circuit?

thanks in advance.

 

[ericgibbs]

thank you so much.

I have one question though. Why the choice of potentiometes in the circuit, why not fixed resistor?
any idea of the purpose of the potentiometers in this circuit?

thanks in advance.

Without those pots its not possible to set the OPA into oscillation, also the pots are needed to stop the clipping of the sine wave output

 

[audioguru]

any idea of the purpose of the potentiometers in this circuit?

Both potentiometers set the output frequency. They should be the same value if the 1nF capacitors are the same value.
Of course the potentiometers can be fixed resistors but then the frequency will be fixed.

 

[kunene]

Of course the potentiometers can be fixed resistors but then the frequency will be fixed.

So then I can use a 5k fixed resistors for both R4 and R5 and still get oscillations?

 

[audioguru]

So then I can use a 5k fixed resistors for both R4 and R5 and still get oscillations?

Yes but nobody makes a 5k fixed resistor.
If the resistors are both 5.1k ohms and the capacitors are both exactly 1nF then the frequency will be about 31.3kHz.

Don't you want 40khz? If the resistors are 3.9k ohms then the frequency will be about 41kHz.

 

[kunene]

If the resistors are both 5.1k ohms and the capacitors are both exactly 1nF then the frequency will be about 31.3kHz.
Don't you want 40khz? If the resistors are 3.9k ohms then the frequency will be about 41kHz.

Understood. By the way, theres this thing I have been meaning to ask, how do you calculate the frequency (meaning the exact formula for this circuit, and i take it it uses R4, R5, C5 and C6)?

 

[kunene]

well, I was able to find out that for the frequency we use the formula: fo = 1/(2πRC).

But could I know for the gain in this case, which resistors we use for the gain, is it R1 and R2 or R1 and R3 (form my first attachment)?

Appreciate any help. thanks

 

[kunene]

hi,
This is the circuit running in LTspice, it may help you to convert to PSpice.

The trim potentiometers are very sensitive in setting.

Hi ericgibbs. I installed LTspice so that I could run the schematic you provided, but I get this message: "Couldn't find symbol(s): potentiometer 2"

Any idea of what I might be missing and need to do? Btw, when the schematic opens, the two potentiometers are not displayed.

thanks in advance.

 

[audioguru]

But could I know for the gain in this case, which resistors we use for the gain, is it R1 and R2 or R1 and R3 (form my first attachment)?

The amplifier is a non-inverting type with its gain (Rf/R3) + 1 but Rf is R1 plus R2. R1 is paralleled by 2 diodes to set the output level.

The gain for a Wien Bridge oscillator needs to be a little more than 3. The gain without the diodes is (1k + 3.9K)/2.2k + 1= 3.23 and the diodes reduce the gain a little if the output tries to become too high.

 

[ericgibbs]

Hi ericgibbs. I installed LTspice so that I could run the schematic you provided, but I get this message: "Couldn't find symbol(s): potentiometer 2"

Any idea of what I might be missing and need to do? Btw, when the schematic opens, the two potentiometers are not displayed.

thanks in advance.

Hi,
I Googled for. pspice potentimometer model

https://ee446.blogspot.co.uk/2008/01/ee446-report-to-j_16.html

I guess you know that two 10K resistors in parallel will give a 5K value.

 

[kunene]

Hi,
I Googled for. pspice potentimometer model

https://ee446.blogspot.co.uk/2008/01/ee446-report-to-j_16.html

I guess you know that two 10K resistors in parallel will give a 5K value.

Thanks, I will try that one.

 

[kunene]

If the didodes are to set the output level, what about the buffer stage (showed in the first attachment), what is its purpose in the circuit?

 

[ericgibbs]

If the didodes are to set the output level, what about the buffer stage (showed in the first attachment), what is its purpose in the circuit?

The buffer is prevent the Wein OPA being loaded by what ever its driving, which could stop it from oscillating or pull the frequency off

 

[kunene]

hi,
This is the circuit running in LTspice, it may help you to convert to PSpice.

The trim potentiometers are very sensitive in setting.

Hi Eric...I actually decided to download LTSPICE and work with it. It is really more interesting than PSPICE from my point of view.

The potentiometer and the opamp, I was able to add from help of one of your other thread. But I have a question concerning the opamp value, it is given by R value and wiper value. what is the wiper value for? and how do we choose it? why should we have the wiper value? how did you choose the wiper value for the schematic you provided?

Hope it is not too much question, but I just want to understand the wiper thing.

Thanks in advance.

 

[ericgibbs]

hi,
The value of the pot in that example is 10K , the wiper value can be set from 0 to 1.

The wiper value indicates the position of the wiper of the pot ie: wp= 0.5 would mean its set to 50%,, 0.1 would be 10% of its rotation.

EDIT:
Simple example showing the pot.

 

[3v0]

test

OP says he can not repley...

 

[kunene]

oh thanks. Can you share GP5V0.sub and asy if you can please. And for the first schematic you shared, is it 10k pot or 5k pot? coz all i see is two 5k pots with different wiper values. sorry for asking too many questions, im just not too familiar with pots.

 

[ericgibbs]

oh thanks. Can you share GP5V0.sub and asy if you can please. And for the first schematic you shared, is it 10k pot or 5k pot? coz all i see is two 5k pots with different wiper values. sorry for asking too many questions, im just not too familiar with pots.

hi,
Rtot is the value as shown ie: 10k

Right click on the Zener diode symbol and select a zener from the pop up box.