Autotransformer is basically huge inductor with sliding contact to get output voltage. This circuit contains 5 inductor of 1 H. Voltage at topmost point is direct input voltage. At 2nd point is 4/5th of Vin, at 3rd point is 3/5th and so on. Sliding contact should be taken care of and should be never open circuited because dangerously high voltage may develop across it. It is because it is never electrically isolated from input like normal 2 winding transformer.
