Both circuits are obviously unauthorized copies from a National Semiconductor application note. See the original document for an explanation
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respectively (seems to be the source of the said circuits, there's one different drawing detail), but this one without explaining text
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I would like to ask the question this way: Which books can help you to become a good designer? Apart from profound text books (e.g. Gray...Meyer), good manufacturer literature (as the said National AN, first released in the 70th, or others from ADI, TI) is instructive in my opinion. I agree, that you are able to design most circuits on your own, just from the basic feedback theory, but sometimes, there's a trick or a special idea...