UCC38C45: Open loop Gain value calculation for DCM Flyback

Sudhanva Gokhale

Part Number: UCC38C45
Other Parts Discussed in Thread: TL431,

Tool/software:

I am using UCC38C45 to design a DCM Flyback converter. As you might be aware there is one pole and one zero in the Open Loop TF of DCM flyback (without TL431 and Opto-coupler). I need the analytical formula for the OPEN LOOP GAIN for the control to output TF so I can adjust the gain of my TL431 and Opto-coupler in the CLOSED LOOP.
I was able to calculate the Open Loop pole and zero but could not find the open loop gain of the DCM flyback with the UCC38C45 datasheet or application notes.
Any help would be appreciated.
Thanks.

1 month ago

0 Pratik Adibatla 1 month ago

TI__Expert 7473 points

Hi There,

We have the below info in datasheet.

You can also use the below app note:

https://www.ti.com/lit/an/snva555/snva555.pdf?ts=1754339421041&ref_url=https%253A%252F%252Fwww.google.com%252F

Hope this helps.

Best,

Pratik A.

0 Sudhanva Gokhale 1 month ago

Prodigy 30 points

The Gplant term for DCM that you mention is specifically used because of a certain IC that is not from TI, the 50*10^3 term in the denominator for DCM. Is this accurate? or will the gain equation be the same for the UCC38C45 IC?

0 Pratik Adibatla 1 month ago in reply to Sudhanva Gokhale

TI__Expert 7473 points

Hello,

That is correct, I found the article on web, I have removed it. You can refer to the app note and the formula given for CCM and convert it for DCM.

0 Sudhanva Gokhale 1 month ago in reply to Pratik Adibatla

Prodigy 30 points

I have seen on the UCC38C45 IC page on TI and it provides an 'Unencrypted Pspice Model', does this model work in LTspice? Please inform.

0 Pratik Adibatla 1 month ago in reply to Sudhanva Gokhale

TI__Expert 7473 points

Yes, an unencrypted Pspice model should generally work in LTSpice. LTspice is designed to be compatible with standard SPICE models, including those written for PSpice. However, some adjustments might be needed due to syntax differences or if the model utilizes specific PSpice features not available in LTspice.

0 Sudhanva Gokhale 1 month ago in reply to Pratik Adibatla

Prodigy 30 points

Sure, I will check it out and let you know the details. Thank you for the help.

0 Pratik Adibatla 1 month ago in reply to Sudhanva Gokhale

TI__Expert 7473 points

Happy to help!

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UCC38C45: Open loop Gain value calculation for DCM Flyback