in this video we will be discussing the autotransformer within the x-ray circuitry system and auto transformers a special type of transformer that is used when a small change in voltage is desired it is different than a traditional transformer in that it only has one coil and that functions is both primary and secondary coils this is accomplished through self induction and the primary aspect of the coil acts as the primary coil and the secondary aspect of the coil acts as a secondary coil the number of terms of the transformer can be controlled and changed as the radiographer makes kVp and MA selections on the control panel taps are slid up and down the coil to select the coils included in the primary and secondary aspects of the coil the specific number of coils included within the primary or secondary aspect determine if the tirado transformer is functioning as a step up or step down transformer determining the turns ratio and resulting voltage of the auto transformer can be accomplished by applying the same equations you learned for transformers the primary turns or NP is the number of terms included within the taps on the primary side of the coil the secondary turns or NS is determined by the turns included in the secondary side of the auto transformer coil in this simple diagram we can see that the auto transformer supplies the current to the high-voltage step-up transformer as well as the filament step-down transformer as mentioned earlier the auto transformer provides the change in voltage needed to create an x-ray image this process starts with 220 volts coming in from the line compensator which ensures an accurate incoming voltage to the auto transformer the technologist makes the appropriate kVp selection on the control panel and as a result the taps on the auto transformer are adjusted to provide the proper voltage to the high voltage transformer for example if the kv p selected was 76 kv p the auto transformer would adjust the 220 volts to 76 volts by functioning as a step-down transformer from here the current of 76 volts is pushed to the step-up transformer with turns ratio of approximately 1,000 to one that will convert the 76 volts to 76,000 volts or 76 kilovolts which is now adequate voltage to create the x-ray image the auto transformer also controls the MA based on selections the radiographer has made on the console the voltage coming in is still 220 volts this moves through the circuit to the auto transformer where the voltage is decreased and the amperage is increased from here the current travels to the step-down filament transformer where the voltage will be further decreased and the amperage increased the high amperage supplied to the filament generates increased friction resulting in more heat which then boils off electrons in what is known as thermionic emission these boiled off electrons are what will be pushed across the x-ray tube when the voltage of the high voltage transformer is applied so what you need to know about the auto transformer you should know that the incoming current to the auto transformer is 220 volts AC or alternating current you should also know that the auto transformer has only one coil but that coil has two sides the primary and the secondary sides you should also know that the auto transformer is used only when a small step up or step down and voltage is required and that it operates on the principle of self induction also note that the auto transformer provides a specific voltage to the high voltage transformer and a specific amperage to the filament transformer both transformers have set turns ratios and so the voltage and amperage coming from the auto transformer will determine the resulting kV and ma used in the creation of the x-ray image lastly make sure to understand the application of the transformer law equation and how to determine the turns ratio you are likely to see these again I hope you found this presentation helpful and you learn something new about Auto transformers in the x-ray circuit