What is the difference between asynchronous and synchronous buck converters?
The difference between asynchronous and synchronous buck converters lies in the device that carries inductor current when the main switch is off. An asynchronous design uses a freewheeling diode. A synchronous design replaces that diode with a second controlled MOSFET.
How does an asynchronous buck converter work?
An asynchronous buck converter uses a Schottky or equivalent freewheeling diode, which gives simple control and robust behavior. Its forward voltage creates conduction loss every switching cycle. At low current this penalty is small, so the simpler design can be the better economic choice.
How does a synchronous buck converter work?
A synchronous buck converter uses a synchronous MOSFET that conducts with low resistance instead of a fixed diode drop. At higher output current, this materially reduces loss and heat. The controller must prevent both MOSFETs conducting simultaneously and manage light-load behavior.
Which factors should you compare when selecting between the two topologies?
Selection involves comparing output current, complexity, thermal load, and cost between the two topologies. The table below summarizes these factors:
| Factor | Asynchronous | Synchronous |
|---|---|---|
| Output current | Often economical at lower current | Advantage grows with current |
| Complexity | Simpler drive | Anti-phase control and protection required |
| Thermal load | Diode loss | Lower conduction loss |
| Cost | Lower component count | Can justify cost through efficiency |
At lower output current, the asynchronous design is often the more economical option, while the synchronous advantage grows with current. The asynchronous drive is simpler, whereas the synchronous approach requires anti-phase control and protection. Thermally, the asynchronous design suffers diode loss, and the synchronous design offers lower conduction loss at a higher component count that efficiency gains can justify.
How should you validate your buck converter choice?
Validate your choice by comparing efficiency at your actual input voltage and load, not only the peak curve. Test startup, transient response and case temperature inside the product enclosure. For application help, contact EVEVSPOWER engineering through the inquiry form.