Magnetizing inductance and Flyback converter

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SUMMARY

The discussion focuses on the representation of magnetizing inductance in flyback converters, specifically its placement in parallel with actual inductance rather than in series with leakage inductance. Participants clarify that the secondary voltage in flyback converters is reflected to the primary side due to the behavior of the output diode and the characteristics of the flyback transformer circuit. The conversation also references a specific PDF document (AN-4147) that illustrates these concepts, emphasizing the importance of understanding the equivalent circuit model of flyback inductors.

PREREQUISITES
  • Understanding of flyback converter topology
  • Familiarity with magnetizing and leakage inductance
  • Knowledge of transformer equivalent circuits
  • Basic principles of diode operation in power electronics
NEXT STEPS
  • Study the equivalent circuit of flyback transformers as detailed in AN-4147
  • Learn about the role of magnetizing inductance in power converter design
  • Investigate the behavior of output diodes in flyback converter applications
  • Explore waveform analysis in flyback converter operation
USEFUL FOR

Electrical engineers, power electronics designers, and students studying converter topologies will benefit from this discussion, particularly those focusing on flyback converter design and analysis.

likephysics
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In the flyback inductor equivalent circuit and also in general, why is magnetizing inductance represented in parallel to the actual inductance?
We can have just the Magnetizing inductance in series with the leakage inductance.

Also, in flyback converters why does the secondary voltage get reflected to the primary side?
 
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likephysics said:
In the flyback inductor equivalent circuit and also in general, why is magnetizing inductance represented in parallel to the actual inductance?
We can have just the Magnetizing inductance in series with the leakage inductance.

Also, in flyback converters why does the secondary voltage get reflected to the primary side?

What's a "flyback inductor"?

Can you post a drawing of the particular circuit you are asking about? Or give a pointer to a typical flyback transformer circuit...
 
berkeman said:
What's a "flyback inductor"?

Can you post a drawing of the particular circuit you are asking about? Or give a pointer to a typical flyback transformer circuit...

See Fig.a in this pdf.
 
likephysics said:
See Fig.a in this pdf.

I'm on it!

Oops, what PDF? :-p
 
likephysics said:
In the flyback inductor equivalent circuit and also in general, why is magnetizing inductance represented in parallel to the actual inductance?
We can have just the Magnetizing inductance in series with the leakage inductance.

Also, in flyback converters why does the secondary voltage get reflected to the primary side?

likephysics said:
See Fig.a in this pdf.

The Lm is in parallel with an ideal transformer, not any other "inductance". And the Lk is in series, as it is usually modeled.

The secondary voltage is "mirrored" or sensed because of the output diode. When the output winding's voltage is below the output voltage plus a diode drop, there is no current flowing in the output.
 
berkeman said:
The Lm is in parallel with an ideal transformer, not any other "inductance". And the Lk is in series, as it is usually modeled.

The secondary voltage is "mirrored" or sensed because of the output diode. When the output winding's voltage is below the output voltage plus a diode drop, there is no current flowing in the output.

The secondary voltage gets reflected to primary because it has no where else to go?
But wouldn't it take some time to get reflected to the primary side?

When the switch (mosfet) goes off, the Drain voltage is at Vdc(or Vin). After some small time when the voltage at secondary is less than output voltage plus diode drop, the voltage is reflected back to primary.
But the waveforms don't show it this way. All the waveforms I have seen show the Drain voltage is Vin+nVo at the instant the switch goes off.
Am I interpreting this right?
 
Last edited:

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