Recently I have been studying feedback in switching power converters, and one thing that is still a bit confusing to me is the way the error amplifier is implemented. Here is what the control diagram looks like from what I understand:
The thing that is still confusing me is the error amplifier. From what I understand, that block takes the difference of the + and - terminals, and passes that to the next stage. In terms of things I know, you could use a difference amplifier such as this:
When I look at other designs online though, it seems like this is not typically how this is done, and instead the op-amp is driven open-loop with a reference on the non-inverting terminal, and the inverting terminal connected to the voltage divider, like this:
I guess in a sense, it is doing the same as the other implementation, except the gain here is much greater. Are both of these approaches valid? What are the advantages/disadvantages of each?