• Is this Method applicable to calculate?
  • My confusion is mainly regarding with Load current.
  • My knowledge is, that load current is nothing to do with saturation of transformer.
  • 1
    \$\begingroup\$ Clarify, do you mean a normal power trnasformer, where Isat is not specified, or a flyback transformer, where Isat is specified? They are intended to work in different ways. Don't use one where the application requires the other. If the former, don't bother. If the latter, calaculate as for the primary inductance. \$\endgroup\$ – Neil_UK May 28 '19 at 8:09
  • \$\begingroup\$ I mean a Power Transformer. \$\endgroup\$ – Israr May 28 '19 at 8:12
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    \$\begingroup\$ As in 50/60 Hz transformer? They don't saturate due to current. Voltage-time-area is what saturates the core according to Vt=NAB or Urms=4.44fNAB. \$\endgroup\$ – winny May 28 '19 at 8:14
  • \$\begingroup\$ My Transformer is a Pulse Trasnformer [Turn Ratio 1:1] used to drive Mosfets.Frequency is 400KHz.Max Load current will be 1.5A. \$\endgroup\$ – Israr May 28 '19 at 8:16
  • \$\begingroup\$ Right. Then it's Vt=NAB and there is no saturation due to current. It's voltage-time area which will saturate it. How do you reset it? Show schematic. \$\endgroup\$ – winny May 28 '19 at 8:45

There are two types of transformer

1) High (ideally infinite) permeability, used as power transformers
2) Low permeability, used as flyback transformers, where \$I_{sat}\$ is a key specification

The difference is that a power transformer is not intended to store energy in the core, that's minimised in the design. While it does have a net current that will saturate it, that current is very small compared to the load current, and we don't control that current directly, as it's the algebraic total current flowing in all the windings. This total current is called the magnetising current. The load current by itself is irrelevant.

In a power transformer, we control the magnetising current by controlling the voltage and time of the input waveform. Each core has a \$Vs\$, a volt.second product, that it can support before core saturation. Increase the input frequency, and you can increase the voltage.

You can calculate the Vs product from the cross section of the core, and knowledge of the maximum field before saturation. Vs = flux (Webers) = core area (m2) * field (Tesla).

In a power transformer, you usually swing from -ve flux to +ve flux, so would use 2x the maximum field. In a pulse transformer, you may be gong from zero field to max, so would only use 1x maximum field. Take care to reset the flux back to zero before the next pulse of the same polarity.

  • \$\begingroup\$ It will work in a bridge like setup.So definitely flux will be reset in negative half. \$\endgroup\$ – Israr May 28 '19 at 15:44
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    \$\begingroup\$ Is the output of the bridge mean zero DC, so 50% fixed duty cycle, or does the duty cycle vary for control reasons? If you put a capacitor in series with the primary, that will guarrantee zero DC at the transformer. \$\endgroup\$ – Neil_UK May 28 '19 at 15:50
  • \$\begingroup\$ Zero DC, there will be a Cap in series with primary.Duty Cycle is 50% fixed. \$\endgroup\$ – Israr May 28 '19 at 19:57

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