sine wave generation using LM 741 in proteus

[hery]

hi, everyone..

I'm newbie here,

would you like to help me how to simulate wein bridge oscilator using LM 741 in proteus?
I have made it.. but it doesn't work..

there is any mistake with my circuit?
the output is square waveform, not sine wave.

 

[duffy]

Looks like you have C2 and R4 connected on the wrong side of R3.

 

[hery]

thanks mr. duffy,
so how i have to placed C2 and R2?

 

[Winterstone]

Looks like you have C2 and R4 connected on the wrong side of R3.

Hery, as mentioned by duffy: Connect C2||R4 to the non-inv. opamp terminal.

 

[hery]

OK, I have done your suggestion, thank you very much

 

[WTP Pepper]

You need some form of AGC on a WEIN oscillator with a minimum gain of 3 (as that's required if you do the sums).
Although your osc on paper has a gain of 3, it won't be enough due to real world components. Increase the gain to 4 but clamp the gain using diodes across the feedback components.

 

[hery]

ok, thank you

 

[Winterstone]

.........Increase the gain to 4 but clamp the gain using diodes across the feedback components.

My suggestion is NOT to increase the gain as high as "4". This design leads to an output signal that is more distorted (due to the diode action) as necessary. The nominal gain must be larger than "3" only by a small amout to cope for resistor tolerances.
Thus a nominal gain of 3.1....3.2 is sufficient and leads to a "soft" opening of the diodes only.

 

[harold777]

This cct needs a gain-limiter, typically a FET or one of those troublesome R53 thermistor (in a vacuum tube!) - but more simply a tiny filament lamp (eg 12v 50mA).

The cucuit diagram is beautifully drawn, but I wonder how come the NFB was omitted . . . or was that deliberate to test Students' understanding....?

 

[Winterstone]

The cucuit diagram is beautifully drawn, but I wonder how come the NFB was omitted . . . or was that deliberate to test Students' understanding....?

If NFB means "negative feedbck" I think it is not omitted. The opamp is designed for a gain of 3.

 

[harold777]

I don't recall a Wien Bridge Osc circuit that doesn't include a non-linear element, seems the gain needs to be adjusted rather finer than a fixed setting.....that's all.
- The trouble with the non-linear elements I mentioned is that they tend to create "bounce" when the frequency is low, (say below 40Hz), since the circuit can "follow" the output amplitude. This causes distortion and makes such circuits unusable below 30Hz (and some may regard 100Hz as the minimum).