Using SiC Power Semiconductors to Increase the Efficiency of High-performance Switching Converters

Silicon carbide (SiC) power devices promise to lower costs and improve efficiency compared to well-established silicon (Si) components. Yet, some designers may still perceive SiC semiconductors to be quite expensive and complicated to control.

Using example SiC devices from Microchip Technology, let’s put those concerns to rest, starting by outlining the fundamental advantages of SiC technology. We’ll then discuss SiC power semiconductors and show the simulation tools, configurable digital gate drivers, and reference designs that can make the development process more manageable.

Small, light, efficient, and cost effective

Many high-performance electrical applications in industrial plants, electric vehicles (EVs), or renewable energy must continuously improve energy conversion efficiency, conserve resources, and lower costs. SiC MOSFETs offer some outstanding advantages for system voltages up to 2000 volts and power levels above 3 kilowatts (kW) compared to the proven Si insulated gate bipolar transistors (IGBTs).

Characterized by steep switching edges and less overshoot, SiC semiconductors achieve extremely low switching losses, up to 70% lower at a switching frequency of 30 kilohertz (kHz) compared to IGBTs (Figure 1). This increases system efficiency and results in lower electromagnetic interference (EMI), minimizing the need for power factor correction (PFC) and line filters.

Figure 1: Compared to IGBTs (top), SiC MOSFETs (bottom) reduce switching losses by more than 70% at a switching frequency of 30 kHz. (Image source: Microchip Technology)

Operating at high switching frequencies, high voltages, and lower currents results in smaller inductive and capacitive components. This reduces weight, wire sizes, and BOM costs. Compared to Si transistors, SiC semiconductors are more stable at higher temperatures and have better heat dissipation, enabling smaller heatsinks to minimize volume.

Due to their high avalanche energy, SiC MOSFETs are robust in unclamped inductive switching (UIS) use cases. SiC MOSFETs are generally very reliable, achieving high power density and tolerating transient short circuits.

Fast, low-loss SiC Schottky barrier diodes

Microchip Technology's SiC semiconductors offer an innovative option for designers seeking improved system efficiency, a smaller form factor, and higher operating temperature for applications such as photovoltaic inverters, battery charging, energy storage, motor drives, uninterruptible power supplies (UPSs), auxiliary power supplies, and switched mode power supplies (SMPS).

Microchip's SiC Schottky barrier diodes (SBDs) are designed with balanced values for surge current, forward voltage, thermal resistance, thermal capacitance, low reverse current, and low switching losses.

SBDs are available in discrete designs, such as the MSC050SDA070BCT dual SBD with a common cathode and TO-247-3 package, which can handle a repetitive reverse recovery voltage (V_RRM) of 700 volts and a forward current (I_F) of 88 amperes (A). The MSC50DC70HJ full-bridge module has screw terminals and can handle 700 volts and 50 A, while the MSCDC50X1201AG three-phase bridge module is designed for through-hole soldering.

High voltage, high current rugged SiC MOSFETs

Newer SiC MOSFETs offer a high UIS capability of approximately 10 to 25 joules per square centimeter (J/cm²). A typical N-channel single transistor like the MSC080SMA120B4 comes in a TO-247-4 package, switches 37 A at a maximum of 1200 volts, and has a separate Kelvin source connection for interference-free gate control.

SiC MOSFET power modules are ideal for switching converter applications in the double and triple-digit kilowatt range. For example, the MSCSM120AM02CT6LIAG half-bridge module features screw terminals and a very low leakage inductance. It contains two N-channel MOSFETs that can safely switch load circuit voltages up to 1200 volts and continuous currents up to 947 A.

The MSCSM120TAM31CT3AG 3-phase half-bridge can handle drain-to-source voltages (V_DSS) up to 1200 volts, switching currents (I_D) up to 89 A, and a maximum power dissipation (P_D) of 395 watts. The integrated SBD freewheeling diodes feature zero reverse recovery, zero forward recovery, and temperature-independent switching.

Digital programmable gate driver

All hardware and software components necessary to operate the low-inductance SiC modules are included in Microchip's Accelerated SiC Development Kit (ASDAK-MSCSM120AM02CT6LIAG-01). The kit includes a ready-to-use digital dual-channel SiC gate driver plug-in board designed to control 1200 volt SiC modules. The gate driver can be programmed for optimum performance using Microchip’s Intelligent Configuration Tool (ICT) and a programming adapter.

The driver board is plugged directly into the SiC module using a suitable adapter card to form a compact half-bridge unit for multi-level on/off operation (Figure 2). The gate drivers support advanced switching control, have robust short-circuit protection, and are entirely software configurable, including +/- V_gs gate voltages.

Figure 2: In the ASDAK-MSCSM120AM02CT6LIAG-01, an adapter card connects a SiC power module to a gate driver board, forming a compact half-bridge power unit. (Image source: Microchip Technology)

Develop quickly and successfully

Another way to easily, quickly, and reliably design SiC semiconductors for your application is to use Microchip's MPLAB SiC Power Simulator. Based on Piecewise Linear Electrical Circuit Simulation (PLECS), the circuit simulator helps designers evaluate SiC devices before building a prototype. It calculates the power losses and estimates junction temperatures for SiC devices using lab test data for common power converter topologies such as DC/AC, AC/DC, and DC/DC applications.

The online MPLAB SiC Power Simulator provides circuit topologies for selection, guides you through component selection, defines operating parameters, and simulates signal curves for voltage, current, power dissipation, and temperature (Figure 3).

Figure 3: The online MPLAB SiC Power Simulator shows the circuit and system parameters on the left and the simulated signal curves on the right. The voltage and current curves of the Vienna 3-phase bridge circuit are shown here. (Image source: Microchip Technology)

Microchip offers many documented SiC-based reference designs, including design files, to help engineers get started quickly. These include power supplies, chargers, and electrical energy storage systems for e-mobility and industrial applications:

• 11 kilowatt (kW) bidirectional DC/DC bridge for EV charging
• 30 kW Vienna 3-phase PFC
• 150 kilovolt-ampere (VA) 3-phase SiC power stack reference design

Conclusion

Microchip’s SiC power semiconductors deliver high system performance in double and triple-digit kilowatt switching converter applications and enable compact, high-power-density designs. In addition, designers benefit from coordinated simulation tools, configurable digital gate drivers, and extensive reference designs to succeed faster with their own circuit designs.