Flyback Converter Turns Ratio
Np/Ns = Vin×D / (Vout×(1−D))
Quick answer
This calculator solves Np/Ns = Vin × D / (Vout × (1 − D)) for Turns Ratio (Np/Ns). With Input Voltage 12 V, Duty Cycle 1.1, Output Voltage 26.4 V, the result is -5. It solves in 4 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
The flyback converter is an isolated switching topology that stores energy in a coupled inductor (flyback transformer) during the switch-on time and delivers it to the secondary during the switch-off time. The turns ratio and duty cycle together determine the voltage conversion ratio. Unlike forward converters, the flyback uses the transformer magnetizing inductance for energy storage rather than transferring energy directly. Flyback converters are popular for low to medium power applications (5-150W) because they require minimal components and provide galvanic isolation.
Variables
- Np/Ns — Primary to secondary turns ratio
- Vin — Input voltage (V)
- D — Duty cycle (0 to 1)
- Vout — Output voltage (V)
Practical Notes
This ideal formula does not account for diode drops, resistive losses, or leakage inductance snubber losses. Practical duty cycles are kept below 0.45-0.5 for continuous conduction mode (CCM) operation. Multiple outputs with different voltages are easily achieved by adding secondary windings. The leakage inductance spike at turn-off requires a snubber circuit (RCD clamp or active clamp) to protect the switch.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| NpNs | Turns Ratio (Np/Ns) | — | — |
| Vin | Input Voltage | V | pV, nV, µV, mV, V, kV |
| D | Duty Cycle | — | —, % |
| Vout | Output Voltage | V | pV, nV, µV, mV, V, kV |
Step by step
- 1. What you know: Input Voltage 12 V, Duty Cycle 1.1, Output Voltage 26.4 V
- 2. The relation: Np/Ns = Vin × D / (Vout × (1 − D))
- 3. Substitute: Vin = 12 V, D = 1.1, Vout = 26.4 V
- 4. Result: Turns Ratio (Np/Ns) = -5
Worked examples
Minimum range
Given: Input Voltage 0.33 V, Duty Cycle 5.5 %, Output Voltage 0.726 V
Result: Turns Ratio (Np/Ns) = 0.02646
Low range
Given: Input Voltage 3.3 V, Duty Cycle 0.55, Output Voltage 7.26 V
Result: Turns Ratio (Np/Ns) = 0.5556
Typical
Given: Input Voltage 12 V, Duty Cycle 1.1, Output Voltage 26.4 V
Result: Turns Ratio (Np/Ns) = -5
High range
Given: Input Voltage 0.23 kV, Duty Cycle 1.76, Output Voltage 0.506 kV
Result: Turns Ratio (Np/Ns) = -1.053
Maximum range
Given: Input Voltage 2.3 kV, Duty Cycle 17.6, Output Voltage 5.06 kV
Result: Turns Ratio (Np/Ns) = -0.4819
Solving for each variable
Solve for Turns Ratio (Np/Ns)
Input Voltage 0.33 V, Duty Cycle 5.5 %, Output Voltage 0.726 V → 0.02646
Solve for Input Voltage
Turns Ratio (Np/Ns) 0.025, Duty Cycle 5.5 %, Output Voltage 0.726 V → 0.3119 V
Solve for Duty Cycle
Turns Ratio (Np/Ns) 0.025, Input Voltage 0.33 V, Output Voltage 0.726 V → 5.213 %
Solve for Output Voltage
Turns Ratio (Np/Ns) 0.025, Input Voltage 0.33 V, Duty Cycle 5.5 % → 0.7683 V
How Turns Ratio (Np/Ns) changes with Input Voltage
| Input Voltage (input) | Turns Ratio (Np/Ns) (result) |
|---|---|
| 1.2 V | -0.5 |
| 3 V | -1.25 |
| 6 V | -2.5 |
| 9 V | -3.75 |
| 12 V | -5 |
| 18 V | -7.5 |
| 24 V | -10 |
| 48 V | -20 |
| 84 V | -35 |
| 120 V | -50 |
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<p><a href="https://vbatpower.com/formulas/flyback-turns/">Flyback Converter Turns Ratio</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Flyback Converter Turns Ratio?
Use Np/Ns = Vin × D / (Vout × (1 − D)). With Input Voltage 12 V, Duty Cycle 1.1, Output Voltage 26.4 V, Turns Ratio (Np/Ns) works out to -5.
What is the formula for Flyback Converter Turns Ratio?
The formula is Np/Ns = Vin × D / (Vout × (1 − D)). The flyback converter is an isolated switching topology that stores energy in a coupled inductor (flyback transformer) during the switch-on time and delivers it to the secondary during the switch-off time.
How do you find Input Voltage when you know the other values?
Rearrange for Input Voltage: with Turns Ratio (Np/Ns) 0.025, Duty Cycle 5.5 %, Output Voltage 0.726 V, Input Voltage is 0.3119 V.
How do you find Duty Cycle when you know the other values?
Rearrange for Duty Cycle: with Turns Ratio (Np/Ns) 0.025, Input Voltage 0.33 V, Output Voltage 0.726 V, Duty Cycle is 5.213 %.
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