Flyback Transformer Calculations

• V_in(min) - Minimum input voltage DC.
• V_in(max) - Maximum input voltage DC.
• V_fb - Flyback voltage
• N_p - Number of primary turns
• N_s - Number of secondary turns
• V_F - Forward voltage drop of diode
• V_out - Output voltage
• t_on - Switch (MOSFET) ON time
• t_off - Switch (MOSFET) OFF time
• P_out - Maximum output power
• L_p - Primary inductance
• I_pp - Primary peak current
• f - Frequency
• D_max - Maximum duty cycle

$$V_{fb} = V_{out} \cdot \frac{N_p}{N_s} = \frac{t_{on}}{t_{off}} \cdot V_{in}$$ https://techweb.rohm.com/knowledge/acdc/acdc_pwm/acdc_pwm01/940/

For Discontinuous Mode

$$P_{out} = \frac{1}{2} \cdot L_p \cdot I_{pp} \cdot f$$

$$I_{pp} = \frac{2 \cdot P_{out}}{V_{in(min)} \cdot D_{max}}$$

$$D_{min} = \frac{ D_{max} }{ (1 - D_{max}) \cdot \frac{V_{in(max)}}{V_{in(min)}} + D_{max} }$$

$$L_p = \frac{ V_{in(min)} \cdot D_{max} }{ I_{pp} \cdot f}$$

https://www.edn.com/flyback-transformer-tutorial-function-and-design/