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# LM324: gain margin/phase margin circuit build

Part Number: LM324
Other Parts Discussed in Thread: TINA-TI

Tool/software:

dear：

can you help me。LM324PWR application circuit is shown in the figure above。

we want to simulation its gain margin/phase margin。

how to build simulation circuit。

• Hello,

We have videos series under TI Precision labs to help guide on stability simulation. The videos specifically show how to set up and post-process in TINA-TI.

https://ti.com/video/4080288067001

https://ti.com/video/6341906518112

Please let me know if you have further questions.
Thank you!

Regards,
Ashley

• dear Ashley

I have watched the video，but i have a question。

Why disconnect the loop? The actual loop is closed loop, is it not more suitable to simulate the actual loop directly。

• Hello user6483709,

The reason we run open loop analysis is due to the mathematical definition of what causes instability.

Acl = Closed loop Gain

B = Feedback factor

Aol = open loop gain

Aol*B = loop gain.

The relationship between the closed loop gain and the open loop gain is such:

Acl = Aol/(1+Aol*B)

So going back to what causes instability, if Aol*B = -1 then  Acl would be undefined as the denominator would be zero. So when we run stability analysis we are looking for when Aol*B = -1. The two parameters left are Aol and B, hence why we want to open the loop to see Aol.

This is covered in more detail in the Stability - 2 video

Hope this helps!

Best Regards,

Robert Clifton