LF411: TINA: LF411: Operating point not found

Hello Avi,

Could you please attach your TINA circuit to assist in troubleshooting your issue?

Best,
Jerry

Hi Avi,

In addition to Jerry's comment, I've noticed that one of your loops is completely floating.  If you trace a path from C1 to R1, then around the feedback components of the first stage, through to C2 and R3, and on through the rest of the feedback section, at no point is any node tied to GND or a voltage source.  So, the circuit has no voltage reference to help if find an operating point.  In other words, that whole part of the network may be floating and that may be the cause of the issue.

If you could share your TINA-TI file with Jerry so he can take a look at it, then this theory could be confirmed or thrown out.

Regards,
Daniel

3phase - autosave 20-10-12 20_31.TSC

Thank you for your reply, Jerry.

Thank you Daniel for your reply, I have tried to put ground at feedback but it is giving me the same error, Btw when I have tried to run before changing anything on Transient--> Calculate on the operating point, it runs from 0% to 100% in 2 seconds and one blank graph appears, no result I can see in that graph. I have shared the file have a look at the comment.

Avi

Hey Daniel, I got the graph for "Transient --> Calculate on the operating point" I solved that issue but still not getting the results for "zero initial value"

Thanks

Avi

Hi Avi,

I see that the output of the circuit is connected to the input. What is the purpose of this circuit? Shall this become an oscillator?

Kai

Hello Avi,

Did you try to use Jerry's latest file referenced above?  I was able to run a transient simulation with the "Calculate operating point" option.

If you can tell us the purpose of your circuit, somewhat, then we might be able to help some more.  Since there is no input, I wonder if this is an oscillator, as Kai has mentioned.  Would that be correct?

Regards,
Daniel

Yes, it is RC phase shift oscillator.

Avi

Hi Avi,

change the "Analysis Parameters":

Kai

Hello Jerry

Thank you for resolving my issue but the output I see, its not oscillate, It should oscillate, Can you please help me out?

Avi 

Hello Avi,

In addition to help you may receive from Kai or Jerry, I'd like to point out a couple of resources.  Balancing the component values for this type of circuit can be very tricky.

Sine-Wave Oscillator

Design of Op Amp Sine Wave Oscillators

Regards,
Daniel

Hey Avi,

Did you follow Kai's advice on changing the "Analysis Parameters" (Analysis-> Set Analysis Parameters, Then click the hand pointing to the right, select "Open", scroll to Oscillators.PRM and select that)

Once I performed a transient analysis it did oscillate (screenshot below)

Best,
Jerry

Hey Jerry

Thank you I got the oscillation now but the frequency I see it in Mhz, which is not possible, Its should be near 400 Hz only. Can you check at your end are you getting the same frequency as mine?

Appreciated

Avi

Thank you so much Kai, Yes it's working but as I said it should work at 400 Hz frequency but it's working on Mhz..

Woohhh Much appreciated for the great resource.

Thanks much Daniel

Avi

Hi Avi,

the oscillation criterium (360° and a gain > 0dB) is not fullfilled at 400Hz, but rather at 400...500kHz:

Kai

Hello Avi,

I am having the same results.  Can you share with us where you found this circuit design?  If you take a look at the design resources I have shared, they will explain how you can pick a low frequency oscillation frequency using the RC components.

Regards,
Daniel

Thank you so much, Kai.

You are welcome :-)

Kai