Turns ratio

Chapter Turns ratio

Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • inductances of the primary and secondary depend on the frequency of operation, andalso on the resistive part of the impedance in the circuit. As the frequency increases,the needed inductance decreases. At high-resistive impedances, more inductance isgenerally needed than at low-resistive impedances328 Transformers and impedance matching18-1Magnetic flux between two coils of wire.Turns ratioThe turns ratio in a transformer is the ratio of the number of turns in the primary, Tpri,to the number of turns in the secondary, Tsec. This ratio is written Tpri:Tsec or Tpri/Tsec.In a transformer with excellent primary-to-secondary coupling, the following rela-tionship always holds:Epri/Esec= Tpri/TsecThat is, the primary-to-secondary voltage ratio is always equal to the primary-to-sec-ondary turns ratio (Fig. 18-2).18-2Primary and secondaryturns and voltages in atransformer. See text fordiscussion.Problem 18-1A transformer has a primary-to-secondary turns ratio of exactly 9:1. The voltage at theprimary is 117 V. What is the voltage at the secondary?This is a step-down transformer. Simply plug in the numbers in the above equationand solve for Esec: