Science & engineering
Ideal transformer ratios
Relate winding turns, RMS voltages, currents and reflected resistance.
A clear answer. Here’s how.
For an ideal transformer, Vs/Vp=Ns/Np, Is=Vs/Rload and Ip=Is×Ns/Np. The load reflected into the primary is Rload×(Np/Ns)². Ideal input/output real powers match for this resistive load. RMS sinusoidal values are magnitudes; winding phase, losses, magnetising current, frequency limits, insulation and ratings are excluded.
See a worked example
Worked example
A fixed demonstration, separate from the values you enter above.
- Primary turns
- 1000
- Secondary turns
- 100
- Primary RMS voltage (V)
- 12
- Secondary resistive load (Ω)
- 10
Example result
- Secondary / primary turns ratio
- 0.1
- Secondary RMS voltage
- 1.2 V
- Secondary RMS current
- 0.12 A
- Primary load RMS current
- 0.012 A
- Reflected primary resistance
- 1,000 Ω
- Ideal load / input real power
- 0.144 W