Magnetizing inductance and Flyback converter

In summary: 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.
  • #1
likephysics
636
2
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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  • #2
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...
 
  • #3
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.
 
  • #4
likephysics said:
See Fig.a in this pdf.

I'm on it!

Oops, what PDF? :tongue2:
 
  • #6
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.
 
  • #7
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:

1. What is magnetizing inductance?

Magnetizing inductance is the property of an inductor that causes it to produce a magnetic field when current flows through it. This magnetic field stores energy in the form of magnetic flux, which can then be released when the current changes.

2. How does magnetizing inductance affect the operation of a flyback converter?

In a flyback converter, the magnetizing inductance is responsible for storing energy during the "on" time of the switching transistor and releasing it during the "off" time. This allows for the conversion of DC to AC voltage and the isolation of the input and output circuits.

3. What factors affect the value of magnetizing inductance in a flyback converter?

The value of magnetizing inductance in a flyback converter is affected by the number of turns in the inductor, the core material, and the operating frequency. A higher number of turns and a higher frequency will result in a higher inductance value.

4. How is magnetizing inductance calculated in a flyback converter?

Magnetizing inductance in a flyback converter can be calculated by measuring the inductance of the inductor with an LCR meter, or by using the equation L = N^2 * μ * A / l, where L is inductance, N is the number of turns, μ is the permeability of the core material, A is the cross-sectional area, and l is the length of the core.

5. What are some common applications of flyback converters?

Flyback converters are commonly used in electronic devices that require isolation between the input and output circuits, such as power adapters, battery chargers, and LED drivers. They are also used in switch-mode power supplies and can be found in many household appliances and automotive electronics.

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