Calculate step-down voltage for transformer, divider, and buck converter circuits, including turns ratio, Vout, duty cycle, and component values.

Ideal circuit estimates. Transformer voltages are AC RMS; load power assumes unity power factor. Divider and buck modes use DC. These estimates do not establish safe component ratings.

Optional settings

Leave blank if unknown. If power is also entered, it must agree with this load.

Leave blank if unknown; used to estimate currents.

100% assumes an ideal transformer. Adjust to estimate input power and current.

Step-Down Voltage Formula

The transformer formula below assumes an ideal AC transformer. Ns must be less than Np for a step-down ratio. Currents and load power use RMS voltage and unity power factor. Divider mode includes an optional parallel load; buck mode provides ideal steady-state continuous-conduction estimates, not final component selections.

SDV = Ns / Np ร— Vp
  • Where SDV is the Step-Down Voltage (volts)
  • Ns is the number of turns in the secondary 
  • Np is the number of turns in the primary 
  • Vp is the voltage in the primary (volts) 

To calculate the step-down voltage, divide the number of turns in the secondary by the number of turns in the primary, then multiply by the primary voltage.

How to Calculate Step-Down Voltage?

The following example problems outline how to calculate Step-Down Voltage.

Example Problem #1

  1. First, determine the number of turns in the secondary. In this example, the number of turns in the secondary is determined to be 14.
  2. Next, determine the number of turns in the primary. For this problem, the number of turns in the primary is measured to be 34.
  3. Next, determine the voltage in the primary (volts). In this case, the voltage in the primary (volts) is found to be 23.
  4. Finally, calculate the Step-Down Voltage using the formula above: 

SDV = Ns/Np * Vp

Inserting the values from above and solving the equation yields: 

SDV = 14/34 * 23 โ‰ˆ 9.470588 (volts)

Example Problem #2

Using the same method as above, determine the variables required by the equation. For this example problem, these are:

number of turns in the secondary = 3

number of turns in the primary = 6

voltage in the primary (volts) = 200

Entering these given values into the calculator or the formula above yields: 

SDV = 3/6 * 200= 100 (volts)