Efficient circuit breakers play a crucial role in the design of on-board and off-board chargers for e-mobility and the RDSon on-state resistance of silicon carbide (SiC) FETs plays an essential role. The lower the resistance of the switch, the lower the heat losses.
The BeFAST evaluation board also provides a ready-to-use development tool for determining all relevant circuit properties in interaction with other essential components such as DC-DC converters, insulators and thermistors.
BeFAST supports the double-pulse testing (DPT) process and the SiC FET are tested in a setup with significantly reduced external influences. This could ultimately lead to a time-to-market benefit of at least 4 weeks.
BeFAST is based on an extremely fast SiC cascode switch from United Silicon’s UF3SC series with the lowest RDSon on-state resistance available to date at less than 9 mOhm at 1200 volts.
The low resistance leads to lower heat losses and thus enables smaller designs. A Murata DC-DC converter integrated in the circuit board combined with a digital isolator from NVE provides a very high pulse strength (CMTI) of over 150 V/ns and an isolation of over 5.2 kV. As an option, the circuit can be extended with sensor components for temperature and current measurement.
The RDSon of less than 9 mOhm at 1200 volts is the lowest value currently available and enables higher switching frequencies than is possible with IGBT, thus enabling smaller designs. Smaller and lighter products are also important when electronics are subject to very high mechanical loads. Compared to large modules, parallel-connection SiC in a TO-247 or as a TO-LL housing offer considerable advantages.
Another benefit is that the reverse recovery charge Qrr of the body diode is virtually temperature independent. The positive temperature coefficient for RDSon is an advantage for parallel connections as the asynchronous load on the switches is minimised. With low leakage and a threshold voltage Vth > 3 V, operation up to a temperature Tj > 200°C (SiC TJMax = 175°C) is possible without the risk of thermal runaway.
For inverters in the field of e-mobility, the very low and virtually temperature-independent switching energies Eon and Eoff of the UF3SC series are ideal, and this is further supported by the excellent recovery characteristics of the body diode.
The SiC FET circuit breakers in BeFast are based on a cascode circuit consisting of a SiC JFET and a Si MOSFET. They can be used in connection with standard gate drivers, making them suitable as a real drop-in replacement for Si IGBTs, Si FETs or SiC MOSFETs. The ISO 15118-20 standard for charging infrastructure means 1200V SiC FETs are also becoming more important for the control of the bidirectional function of charging units, i.e. the control of active power P and reactive power Q.
The main benefit of the evaluation board is to test and characterise the high requirements with regard to aspects such as speed, isolation, pulse strength and efficiency in direct interaction without having to develop a prototype.
The evaluation kit is delivered with detailed documentation such as the precise parts list, design files (layout and Gerber) and application notes.
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