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# UCC3808A-2: PID Implementation in DC/DC converter (PPull), which output voltage measurement is achieved through an isolated amplifier

Part Number: UCC3808A-2

Hello,

I am measuring the output voltage through a little sample of the it (voltage divider), and then a isolated Oamp is connected. I would like to know if what I am doing is right:

The UCC3808A-2 has particularly 2 pins to place the compesation network: FB (Inverting input to the error amplifier) and Comp (Output of the error amplifier and the input of the PWM comparator).

The proportional component of the controller is implemented through a Oamp after the Isolated Oamp (this last has unitary gain). Then I have placed the derivative element, which is achieved with a RC in parallel, and it is connected to the FB pin; the integral component of the compensator is placed between FB and COMP as a RC series network (see Figure).

1. Is the PID well implemented?

2. Does the block diagram in the figure represent the previous mentioned configuration?

Thank you for your help.

Best regards,

David

• Hi David,

Thanks for your interest in UCC3808A. Please allow us to review your post and get back to you early next week.

Best Regards,
Ben Lough
• Hi David,

You block diagram looks correct. I have include a link to a good paper on power supply control loop compensation, www.ti.com/.../slup173.pdf. This paper will give you a useful insight into the control loop theory.

Regards

Peter
• Hi Peter,

Thank you for your help. That paper did help me a lot.

I have a two question related with the block diagram for the Current Mode Control (CMC) presented in that paper:

Taking the FIgure 12 and setting the values of Q1(s), F1(s) and F2(s) to the values for the CMC (given in Figure 22) will result in something like the attached figure.

• Although they are given, how can I define mathematically/analytically Q1(s), F1(s) and F2(s)? I have tried several ways, but I do not get those terms. Could you give me a clue, please?
• Just assuming that those terms are given, I know where does the final G(s)H(s) come from, but I don't know where did (D/LC)(1-gamma/(1-D)  (in red color) term come.  Could you give me an Idea to define it?

Once again,  THANK YOU for your help

Best Regards,

David.

• Hi David,

The answer to your questions require long and detailed explanations.

Please can I suggest the following book. It gives all the details you require presented in a very clear understandable way.

"Fundamentals of Power Electronics" by Robert W. Erickson and Dragan Maksimovic.

Thanks

Joe Leisten