Sinrace Power Supply Technology (Shenzhen) Co., Ltd.

Despite the substantial reductions in power system size over the last decade, no single design leap has made this possible. Rather, a combination of small improvements in both design techniques and components technologies have come together to create the end result. Taking power supply from input to output, these are some of the design approaches that are now adopted.

Two-stage input filters use high permeability cores to minimize size while providing high common-mode and differential noise reduction. Smaller footprints can be realized by stacking components vertically. This can also improve cooling through better airflow.

In many power supplies, it has become economical to use silicon carbide (SiC) diodes in power-factor correction (PFC) circuits. These need no snubber circuits, reducing component count and saving space while giving a typical 1% boost to efficiency.

The main converter topology is critical to efficiency. For power supplies in the 100 to 200 W range, a resonant topology is often chosen. This can virtually eliminate switching losses, enabling smaller heat sinks to be used, thus contributing to the dual goals of smaller size and higher efficiency. In some cases, ceramic heat sinks can replace metal ones.

This results in lower noise because the heat sinks are not subject to capacitive coupling with the drain connections of the switching MOSFETS. Simplified filtering can then be used. An additional advantage of ceramic heat sinks is that smaller creepage distances can be used, compared with those needed for conductive metal heat sinks, so further board space savings are achieved.

The falling price of power MOSFETS has meant that they are now becoming more common than diodes in the main rectifier of switching power supplies. Efficiency improvements of more than 40% in this part of the circuit are possible. For example, a 20 A diode with 0.5 V forward voltage dissipates 10 W, whereas a MOSFET with an 'ON' resistance of, say, 14 mΩ at 100° C dissipates just 5.6 W. Once again, ceramic heat sinks can be used to advantage.
Lastly, control circuits have been greatly simplified in recent years, largely through higher integration of semiconductor functions. Application-specific chips are now available that can provide the main converter voltage and a host of automatic protection features. Comprehensive monitoring and control signals are also more easily implemented thanks to more highly integrated power management devices