Silicon carbide (SiC) MOSFET has become a potential substitute for silicon (Si) IGBT and is widely used in photovoltaic inverters, on-board and off-board battery chargers, traction inverters, etc. Compared with Si IGBT, SiC MOSFET has more stringent requirements for short-circuit protection.

MicroBi Semiconductor's SiC MOSFET has unique advantages in short-circuit protection solutions, which can help design engineers achieve more efficient and reliable power electronic systems. By rationally selecting and applying short-circuit protection solutions, combined with the excellent characteristics of SiC MOSFET, it can ensure the maximization of system robustness and device efficiency, and promote further development and innovation in the field of power electronics.

This article will explore the differences between SiC MOSFET and Si IGBT, describe and compare three short-circuit protection methods in detail, and summarize the special requirements of SiC MOSFET in short-circuit protection.

Short-circuit protection is very important to ensure the system is robust and fully utilizes the device. A qualified short-circuit protection circuit should be able to quickly detect and shut down the device without false triggering. We will analyze and compare the three commonly used short-circuit protection schemes, including desaturation detection, shunt resistor detection, and senseFET current detection.

Desaturation Detection Scheme

Figure 1 shows the construction of a desaturation detection circuit.

 The circuit consists of a resistor, a blanking capacitor, and a diode.

When the device is turned on, the current source is used to charge the blanking capacitor and turn on the diode. Under normal operating conditions, the capacitor voltage is fixed at the forward voltage of the device. When a short circuit occurs, the capacitor voltage quickly charges to the threshold voltage, triggering the device to turn off.

For IGBTs, the desaturation threshold voltage is usually set near the switching voltage to ensure that the current is limited after this, allowing the IGBT to withstand longer. However, designing the desaturation circuit for SiC MOSFETs requires more attention. Since the switching voltage of SiC MOSFETs is usually high and cannot limit the current, the desaturation threshold voltage needs to be set to a lower value when the recommended short-circuit turn-off time is less than 2μs. In addition, the fast switching speed of SiC MOSFETs may generate noise during the turn-on transition, so the short-circuit detection time should be designed to be long enough to avoid false triggering, which brings challenges to the desaturation circuit design of SiC MOSFETs.

Shunt Resistor Detection Solution

Figure 2 shows a shunt resistor sensing scheme that senses current by placing a small resistor in series with the power loop.

 This solution is straightforward and can be flexibly applied in various systems. However, to ensure signal accuracy and detection time, high-precision resistors and fast ADCs are required.

The disadvantage of this method is power loss . In high-power systems, large currents will cause large power losses in the shunt resistor; while in low-power systems, larger resistors are required to ensure signal accuracy, which will also lead to losses and reduced efficiency in low-power applications.

senseFET current detection solution

Figure 3 shows a senseFET current sensing solution. Usually, the senseFET is integrated into the power module and connected in parallel with the main device to reduce the device current.

The reduced current is then measured using a precision shunt resistor. This approach effectively reduces device current and provides accurate current sensing, making it a widely used method in modern systems.

 As a high-performance, high-efficiency option, SiC (Silicon Carbide) devices are gaining more and more attention. MicroBi Semiconductor's SiC MOSFET has some unique advantages and application value in short-circuit protection solutions.

High-speed switching characteristics: SiC MOSFET has faster switching speed and lower conduction loss than traditional Si (silicon) devices. This allows SiC MOSFET to respond faster and cut off current when a short circuit occurs, reducing system losses and the risk of device damage.

High temperature performance: SiC devices have better high temperature characteristics and can operate at higher temperatures without losing performance. This is especially important for short-circuit protection, because under high load and high temperature environments, SiC MOSFET can work more stably to ensure system reliability.

Low switching losses: The low conduction and switching losses of SiC MOSFETs mean that the system is more efficient under normal operating conditions. When short-circuit protection is triggered, the fast switching characteristics can quickly cut off the current and reduce system energy loss.

High integration: MicroBi Semiconductor's SiC MOSFET can be integrated with other protection circuits and control circuits to provide a more comprehensive short-circuit protection solution. This level of integration can simplify system design, reduce system size, and improve overall system performance.

 In summary, choosing a suitable short-circuit protection solution is crucial to ensure the safe operation of the system and the long-term robustness of the device. Each solution has its advantages and limitations, so in actual design, it is necessary to comprehensively consider system requirements and device characteristics to find the best solution.