Synchronous vs Asynchronous Buck: What’s the Difference?

When a MOSFET replaces the freewheeling diode, efficiency rises — here is how synchronous rectification works and when it pays off.

The freewheeling element is what separates the two classic buck converter designs. In an asynchronous (non-synchronous) buck, a Schottky diode carries current during the off phase. In a synchronous buck, that diode is replaced by a second MOSFET that is switched in anti-phase with the main switch.

Why synchronous wins on efficiency

  • A diode has a fixed forward voltage drop (0.3–0.5V), which becomes a meaningful loss at high current.
  • A MOSFET’s on-resistance (RDS(on)) produces a much smaller, current-scaled loss.
  • Lower conduction loss means less heat, smaller heatsinks and higher overall efficiency.

When asynchronous still makes sense

Non-synchronous designs are simpler, cheaper and perfectly adequate at low current or where cost matters most. That is why we offer both.

EVEVSPOWER boost converters benefit too

The same synchronous-rectification technique pushes our boost converters to efficiencies up to 98%, with a bypass pass-through function when the input already exceeds the target output. Browse the boost family or ask for a comparison.