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The problem is as below.

Input DC voltage is at 12V, transformer inductances are: Lp = 60uH, Ls = 240uH, switching behaviour is controlled by a single NMOS with switching frequency at 60kHz.

For ideal case, is it correct that power at primary winding is equal to the power at secondary winding, and that is the equation for this power.

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  • \$\begingroup\$ Yes, and in terms of basics, you need Lenz's Law to help find the power. \$\endgroup\$ – Brian Drummond Oct 30 '18 at 7:56
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For ideal case, is it correct that power at primary winding is equal to the power at secondary winding, and that is the equation for this power.

With ideal switches and diodes, zero transformer losses and switching losses and 100% transformer coupling, yes, all of the net energy taken by the primary winding is transferred to the secondary winding in the 2nd part of the switching cycle and that net energy multiplied by the switching frequency equals the power transferred.

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  • \$\begingroup\$ Sorry, I hit enter before finishing the comment. I've found on the internet for these equations as follow: Pin = 0.5*LpIp_peak^2*fsw = 0.5*Vin^2*D^2/(Lpfsw) (D is duty cycle, fsw is FET switching frequency, and Ip_peak is the peak winding current). Are these equations correct. \$\endgroup\$ – Electronics newbie Oct 30 '18 at 8:04
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    \$\begingroup\$ @Electronicsnewbie stades.co.uk/Flyback/flyback%20DCM2.html \$\endgroup\$ – JonRB Oct 30 '18 at 9:45
  • \$\begingroup\$ @Electronicsnewbie Power = energy x frequency and \$0.5\cdot L_P\cdot I_P^2\$ is the stored energy in the inductor. So, if all that energy is transferred to the secondary then so is all that power (assuming zero losses.) \$\endgroup\$ – Andy aka Oct 30 '18 at 11:39
  • \$\begingroup\$ Follow JonRB's link to the section called "VBUS to VOUT transfer ratio" and you'll see that your 2nd formula should be \$F_{SW}^2\$ in the denominator. \$\endgroup\$ – Andy aka Oct 30 '18 at 11:45

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