2-Transistor Forward Converter

Used for: Isolated supplies where switch voltage must be limited and where 50% duty cycle max is acceptable


  • Switch voltage stress is clamped to Vcc
  • Leakage inductance energy is returned to the supply
  • No snubber needed
  • Transformer primary connections swing symmetrically - can can cancel EMI if mechanical layout considered


  • Two switches needed
  • High-side gate drive needed
  • Duty cycle limited to 50%


  • Same as forward converter except two transistors switch the transformer primary
  • Each end of the transformer pri alternately goes to supply and 0V
  • This means each transistor has voltage limited to supply rail max
  • This in turn limits reset voltage to supply
  • This in turn limits duty cycle to 50%
  • V0 = VinD . Nsec/Npri