Transformers can step up or step down voltages and currents, and allow AC to pass while blocking DC. They consist of primary and secondary windings wound around an iron core, with no electrical connection between windings. The voltage induced in the secondary winding depends on the ratio of turns between the windings. Auto transformers have a single winding used for both primary and secondary, providing no electrical isolation and allowing the full voltage to pass to the load if open circuited. Transformer rectifier units convert AC to DC using a transformer to step down the voltage which is then rectified.

6. Categorise of Transformer Figure 9-2 Set up and Step down Transformers

12. Auto transformers

25. Figure 9-10 Typical TRUs on Aircraft

29. END OF CHAPTER 9