Explanation

• • The transformer equation E = 4.44(f)(B)(N)(a)

Where,

• • E is the voltage in the winding either primary or secondary,
  • f is the frequency,
  • B is the flux density in the core,
  • N are the number of turns on the winding, and
  • a is the cross area of the core.
  • At higher frequencies the number of winding turns N is reduced.
• This formula follows from the Faraday formula, E = N dθ/dt and θ = B(a).
• This formula is switching power supplies use a much higher frequency (thousands of hertz) than 60 hertz, they use smaller transformers that don’t need as much wire as transformers operating at 60 hertz.