As you look at the schematics, you'll see that many are a variation on one theme - a centertapped primary with the tap connected to the + DC source, and two power transistors driven out of phase pulling each end of the primary to ground. This produces either a squarewave or modified squarewave output, very common in low cost inverters. Note that only half of the primary is driven at any time, and this changes the required turns ratio.
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