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Ideal Transformer Turns, Voltage & Current Ratio

Explore ideal transformer voltage and load-current magnitudes from a positive turns ratio.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

With 100 primary turns and 50 secondary turns, 12 V primary gives 6 V secondary. A 2 A primary load current corresponds to 4 A secondary in the ideal model.

Vs/Vp = Ns/Np; Is/Ip = Np/Ns

Worked example

Enter these known values and leave the other values blank.

Primary effective turns
100
Secondary effective turns
50
Primary voltage magnitude
12 V
Primary load-current magnitude
2 A
Secondary voltage magnitude
6 V
Secondary load-current magnitude
4 A

Assumptions and limitations

  • This is a lossless ideal transformer under AC excitation. Voltage and current are nonnegative magnitudes, and both effective turns values must be positive.
  • Use a consistent amplitude convention on both sides; RMS magnitudes are appropriate for sinusoidal steady-state power comparison. Phase and winding-dot polarity are not represented.
  • The model omits magnetizing current, leakage, saturation, resistance, losses and loading limits. It does not describe a real transformer connected to steady DC.
  • Fractional effective turns can represent an ideal ratio algebraically; they do not specify a directly manufacturable whole-turn winding. Zero voltage/current cases do not uniquely determine every inverse ratio.

Common questions

Does stepping voltage down also step current down?

In the ideal load-current relationship, current changes inversely with voltage so that input and output real power remain equal under the same load power factor.

Does the calculation determine an actual transformer rating?

No. Ratings depend on core, winding, insulation, frequency, cooling and other design limits omitted by this model.

References

Bookify treats transformer voltage and current inputs as nonnegative magnitudes; positive turns ratios are retained.

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