Flyback Converter Design (NEW)

• Needs:

  • 50-600V to 12V DC step-down
  • Max current of ~1A

• Optional:

  • direct 5V rail

• DCM vs CCM

• Want lower losses, thus CCM > DCM

• CCM more complicated but should fit needs

  • Larger transformer required
  • Smaller V_out (i.e. gain), ok since we only want 12V
  • Transfer function is much more complicated than LC tank (DCM)

• Misc flyback math articles

  How to Design a Flyback Converter in Seven Steps

  Designing Isolated Flyback Converter Circuits: Transformer Design (Calculating numerical values) | Basic Knowledge | ROHM TECH WEB

Parameter Calculations

• Choose $D=0.5$ duty cycle of 50%

  • Equal load on MOSFET and diode

• $V_{out}=12V$

• $V_{in}=[400V,600V]$

• $I_{out}=1A$

• Operation mode desired: CCM

• Relation between windings and voltage for a transformer

  • p=primary (input), s=secondary (output)
  • N=# of windings
  • V=voltage

• In this case, $V_p=V_{in}$ but $V_s \ne V_{out}$, instead $V_s=V_f+V_{out}$ where $V_f$ is the forward voltage across the diode

  $$ \frac{N_p}{N_s}=\frac{V_p}{V_s} $$

$$ \frac{N_p}{N_s}=\frac{V_p}{V_s}=\frac{V_{in}}{V_f+V_{out}} $$

Design