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I want to understand how LM2574 step-down regulator works and I can not find the logic of the comparator in the following picture: Can anyone explain ? enter image description here

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The usual method is to use the comparator with a triangle clock generator with the linear error converted to PWM (pulse width modulation) to control the buck regulator. I show my example below as a simplified version of this IC. (not optimized)

enter image description here Here a simple Schmitt astable clock can be integrated by some RC inside to create a fairly linear triangle at the right amplitude. (<~1/3) but must exceed the range of the linear error. It will not be implemented as shown here but with discrete transistors.

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