Turns ratio
The ratio n = U1/U2 = N1/N2 between primary and secondary.
Definition
The turns ratio, denoted m or n, is the ratio between a transformer’s primary and secondary voltage. It is set directly by the ratio of the numbers of turns: m = U1/U2 = N1/N2. It is the parameter that defines whether the transformer is step-down (m > 1) or step-up (m < 1).
The turns ratio also relates the currents, but inversely: I2/I1 = N1/N2. A transformer that lowers the voltage raises the current available at the secondary by the same factor (losses aside), in accordance with the conservation of power.
In practice, the ratio is calculated at no load; under load, the internal voltage drop due to impedance slightly lowers the actual secondary voltage.
The ABL tip
Tell us the primary and secondary voltages you want under load: we calculate the number of turns and the necessary compensation to deliver exactly your output voltage in operation, not just at no load.
