The Inversion Does Not Care Which Way You Step
The Inversion Does Not Care Which Way You Step
A buck converter always steps down. A boost converter always steps up. Their names describe the one thing each circuit is committed to. The buck-boost converter, wired with a single inductor, a single switch, and a single diode, is committed to neither. Its output voltage gain is a single continuous formula, D/(1-D), where D is the duty cycle — the fraction of each switching cycle the transistor spends on. Feed D below one half and the circuit steps down, buck-fashion. Feed D above one half and the same circuit, unchanged, steps up, boost-fashion. The crossing at D = 0.5, where gain equals exactly one, is not a seam between two different machines. It is one point on one curve, and the curve does not know it has passed through anything.
But the article is precise about a second fact riding underneath the first, one that does not move when duty cycle moves at all: in the inverting topology, the output polarity is always the opposite of the input's, for every value of D from 0 to 1. Whether the circuit is stepping the magnitude down toward zero or up toward theoretical infinity, the sign flips regardless. Stepping and inverting are two separate facts about the same circuit, governed by two separate mechanisms — one continuous and duty-cycle-dependent, the other fixed and topology-dependent — and the article keeps them apart on purpose. A non-inverting variant exists precisely by breaking only the second fact while keeping the first: swap diodes for a second switch, and the same buck/boost continuum survives with the polarity flip removed.
So "buck-boost" names a spectrum, one number sliding a gain curve through unity. It does not name the inversion. That fact was never on the dial at all.