Cloud-server designers demand more board space for processors and FPGAs to handle heavy compute loads, whereas EV designers seek compact inverters for car packing.
FREMONT, CA: Exotic technologies such as silicon carbide (SiC) and gallium nitride (GaN) have become more affordable as energy costs rise. Economies of scale make SiC or GaN transistors and diodes cheaper as markets grow. Power conversion industry power, temperature, and cost requirements need high-efficiency power MOSFETs, rectifier diodes, and IGBTs. As the devices become more common in power circuits, particularly appliance or electric vehicle (EV) motor drivers, designers must consider their effects on passive components like capacitors and how to design them to maximize efficiency gains and reliability.
Diodes and MOSFETs save energy in numerous ways. SiC diodes have a shorter reverse-recovery time than silicon diodes, allowing faster switching. SiC MOSFETs do not have the tail current that characterizes the turn-off behavior of typical silicon IGBTs. They can reduce turn-off loss by up to 90 percent while increasing switching frequency and eliminating the need for additional capacitance for smoothing. The large bandgap of SiC allows high-voltage transistors to be constructed with an exceptionally narrow channel, resulting in low RDS(ON) per unit area and reduced conduction losses than silicon devices in regular power packages.
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High breakdown voltage and low switching and conduction losses allow efficient high-voltage circuits with low distribution currents and I2R losses. In circuits like data center power supply, servers need more power to accommodate rising compute loads due to trends like more subscribers, consumer demand for streaming services, increased use of Cloud analytics and storage, and the emerging Internet of Things (IoT). Wide bandgap devices filter and smooth voltage, and current ripples with lower external capacitance due to increased operating voltage and switching frequencies.
The size of power circuitry is often constrained by extreme factors; capacitors must have high voltage ratings and small case sizes.
Cloud-server designers want to maximize board real estate for processors and FPGAs to handle high compute loads, while EV designers want small inverters to help with vehicle packaging. Components for wide bandgap semiconductors (WGS) must also endure greater ambient temperatures, and SiC or GaN devices run at higher temperatures than silicon devices with comparable reliability. System designers can use this to simplify thermal management and reduce cost and size. Appliance makers can save money with a smaller heatsink, data centers can save on server room air-conditioning, and EV-inverter cooling systems can reduce vehicle weight and cost.
Components like capacitors get closer to hot power semiconductors because wide bandgap devices use higher switching frequencies requiring short wire lengths to minimize inductance. Designers must boost capacitor temperature ratings and stability to achieve enough capacitance at the average steady-state working temperature. Low capacitor ESL and ESR reduce self-heating and high-frequency induced voltages. High operating frequencies require careful circuit layout to minimize inductance in PCB traces and connections.
