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I will be using the UC3844 controller IC in combination with TL431 to achieve peak current mode control in a 150W forward converter. After some research, I found this schematic on the internet:

enter image description here

There are two compensation networks present here(shown in red rectangles).

These are the questions that I have:

  1. Can anyone please elaborate which network is used to compensate what?
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The right hand red box is not a compensating circuit; it just uses the TL431 as a voltage comparator and starts putting current into the opto LED as soon as the output target voltage is reached. This type of design is massively commonplace and used all over but, it isn't a compensation network in the sense that I think you mean.

The left hand red box has a bunch of NU components and, NU means not used so, if you remove those from that circuit, you will see that there is just the basic type of compensation required by the UC3844.

Don't let circuit clutter smoke screen the truth: -

enter image description here

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  • \$\begingroup\$ Okay, so does that mean if the original designer would have implemented the compensation using the TL431 itself, he wouldn't have to make the compensation circuit in the green box? And if that's the case, is there any advantage or disadvantage of implementing the compensation on the primary side instead of on the secondary side with TL431? \$\endgroup\$
    – tinkerer
    Commented Nov 5, 2021 at 8:20
  • \$\begingroup\$ All the compensation in your circuit is on the primary side and that is because it's close to the op-amp inside the UC3844. In my opinion that is the best place to compensate. I've never seen anyone perform the whole of the compensation entirely on the TL431 side. In fact, what we see above is normal i.e. compensation entirely on the primary side. \$\endgroup\$
    – Andy aka
    Commented Nov 5, 2021 at 8:24

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