To achieve the buck/Increase function, everything is needed is 2 individual switches so the AC input might be connected to one of many two primary taps, when the load is linked to one other, Hence utilizing the most important transformer's primary windings being an autotransformer. Case in point #7 - https://andrecfdbz.luwebs.com/34469514/uninterruptible-power-supply-system-an-overview