Calculating Inductance for 5kV Flyback Converter in 1mS

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Discussion Overview

The discussion revolves around calculating the inductance required for a flyback inductor in a boost converter to achieve 5kV across the inductor in 1ms with a current of 10mA. Participants explore the relevant formulas and considerations for high voltage applications.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant inquires about the inductance needed using the formula V=L di/dt, expressing uncertainty in rearranging it for the correct answer.
  • Another participant reiterates the same question and suggests that di/dt can be defined as 10A/sec, prompting a calculation for inductance in Henries.
  • A third participant provides a reference to the definition of the Henry unit, indicating a formula related to inductance.
  • One participant argues that the flyback boost voltage does not depend on the primary inductance, emphasizing that primary inductance and peak current determine the energy transferred rather than voltage.
  • This participant also notes that when the main switch opens, the L di/dt can be very large and mentions the importance of managing secondary voltage to prevent damage to the switch.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between inductance and voltage in flyback converters, indicating that multiple competing perspectives remain without a consensus on the calculations or principles involved.

Contextual Notes

Participants highlight the need for caution in high voltage applications, mentioning safety hazards and the requirement for specialized expertise in building high voltage inductors.

hobbs125
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I am wondering, In a flyback inductor used for a boost converter, what inductance would be required to produce 5kV across the flyback inductor in 1mS with a current of 10mA?


I know the formula would probably be V=L di/dt but I'm not sure how to rearrange it to get the correct answer.
 
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hobbs125 said:
I am wondering, In a flyback inductor used for a boost converter, what inductance would be required to produce 5kV across the flyback inductor in 1mS with a current of 10mA?I know the formula would probably be V=L di/dt but I'm not sure how to rearrange it to get the correct answer.
di/dt is simply the rate of change of current which you defined as 10A/sec. Solve for the inductance L in Henries.

Please exercise caution if this is other than an academic exercise. And, aside from the obvious safety hazards, building high voltage inductors requires other expertise - special insulating materials, placement, etc.
 
H=V.s/A refer this
http://en.wikipedia.org/wiki/Henry_(unit )
 
Last edited by a moderator:
The Flyback boost voltage doesn't really depend on the primary inductance.

The primary inductance together with the peak current defines the amount of energy (not voltage) that the coil can transfer on each cycle.

When the main switch opens, you can treat that as instantaneous. L di/dt can be huge. In a real Flyback, you allow the secondary voltage to go up to some particular voltage by connecting the secondary to a capacitor.

If for some insane reason you want the secondary voltage to go really high, you have to take steps to make sure that voltage isn't transformed back to the primary side where it will probably destroy the switch.
 

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