Low Cost, 28 Watt PWM Flyback Converter

Via- 18 to 36 VDC required operational range +24 VDC nominal input line voltage 

This indicates that a 18 AWG wire or equivalent should be used on the primary winding of the transformer. 

Select the frequency of operation of the power supply to be 40 kHz (or Poiymax) = 12.5 uS). 

I will use an MPP toroid core. The core sizing procedure is contained in Section 3.5.5. Estimate the core size required  

The number of secondary turns on the lowest voltage (-1-5 V) output (assuming a Schottky rectifier) is 

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