Synchronous Rectification Advantages

So what advantages can synchronous rectification bring? The energy loss of synchronous rectification mainly comes from the conduction loss of MosFET, and the conduction loss of MosFET is basically determined by its internal resistance. Generally, MosFETs suitable for synchronous rectification have extremely low internal resistance, most of which are only about 5mΩ, so the output current is also 10A. Schottky rectification may bring about 4W loss, while synchronous rectification is based on P=I2R The formula can calculate the loss as 10A10A0.005Ω=0.5W, and the loss under the same output is only one-eighth of Schottky rectification, so the conversion efficiency of synchronous rectification is much higher than that of Schottky rectification. It can reach the level of 90% or even 95%.

Most synchronous rectified MosFETs have only 4mΩ to 5mΩ internal resistance.

Compared with Schottky rectification, the difficulty of adjusting synchronous rectification lies in the adjustment of its driving circuit. Therefore, in the early development of PC power supply, synchronous rectification is generally only used in high-end products, as a means to demonstrate the strength of manufacturers. Most mainstream products use Schottky rectification with a simple circuit structure. In recent years, the driver IC of synchronous rectification has made great progress, making the control of synchronous rectification no longer a difficult task, so now synchronous rectification has gradually advanced from the high-end to the mainstream market.

In addition, synchronous rectification has another advantage over Schottky rectification, that is, in the case of light-load output, due to the unidirectional conduction of the diode, the output of Schottky rectification will enter the discontinuous mode, the current waveform is intermittent, and the voltage It will generate ringing and release high-frequency harmonics; and the transistor used in synchronous rectification allows the current to pass in the reverse direction, so the current waveform is continuous, and the circuit can always work in a continuous state, but because the reverse current is output by the capacitor, it is light. The synchronous rectification circuit under load does not have obvious advantages over Schottky rectification in terms of conversion efficiency, but compared with the latter's disadvantage of releasing high-frequency harmonics, the "defect" of the synchronous rectification circuit under light load is almost negligible. Does not count.