Lately, a lot consideration has been centered on Silicon carbide (SiC) and its potential use in energy electronics, however this has additionally generated some misconceptions. Listed below are a few of the commonest misconceptions─and the truths─ so engineers might be extra assured about utilizing Silicon carbide units sooner or later.
Purposes
A few of the confusion surrounding Silicon carbide relate to the purposes the place it may be used. For instance, some designers imagine that Silicon carbide MOSFETs needs to be used to exchange IGBTs, whereas gallium nitride (GaN) units ought to exchange silicon MOSFETs. Nevertheless, 650 V-rated Silicon carbide MOSFETs supply glorious efficiency with a aggressive RDS(ON)*Qg figure-of-merit and minimal reverse restoration cost. This makes Silicon carbide a great various to silicon MOSFETs in laborious switching purposes like totem pole energy issue correction (TPPFC) or a synchronous increase.
Some engineers imagine that Silicon carbide isn’t effectively suited to increased frequency purposes and that GaN needs to be used as an alternative for quick switching. Nevertheless, current technological advances have diminished Silicon carbide die space, additional growing its suitability for high-frequency (>100 kHz) operation. Because of this, Silicon carbide units are actually getting used efficiently in purposes like TPPFC at 100 kHz and soft-switching LLC at frequencies between 200 and 300 kHz.
Moreover, rising applied sciences like trench and Cascoded Silicon carbide MOSFETs will improve its high-frequency efficiency much more. Lastly, different engineers imagine that Silicon carbide is a distinct segment know-how based mostly on its success in EV traction inverters. Nevertheless, the requirement for elevated energy density and environment friendly operation throughout virtually all sectors signifies that the advantages of Silicon carbide may also profit a broad vary of much less complicated designs like EV onboard chargers (OBC), photo voltaic photovoltaic (PV) modules and renewables, in addition to cloud computing.
Fig. 1. Silicon carbide wafers.
Machine Choice and Operation
Many designers use a unfavorable turn-off gate voltage to forestall SiC units from ‘bouncing’ or inadvertently turning again on attributable to switching transients, however this isn’t a strict requirement. Many examples of profitable SiC designs wouldn’t have a unfavorable gate voltage drive. Nevertheless, as with all designs, good practices needs to be adopted, such a decent structure that minimizes parasitic results. Additional, the gate driver ought to be capable to sink adequate present to carry the system off firmly. A junction-isolated gate driver could also be acceptable in a restricted variety of purposes, corresponding to TPPFC. Nevertheless, it’s value noting that galvanically remoted gate drivers supply enhanced noise immunity and might higher deal with swap node dv/dt transients, stopping false tripping.
As SiC MOSFETs swap quickly and have decrease gate cost (Qg) than equal silicon units, a galvanically remoted gate driver makes for a extra strong design – even in purposes that don’t strictly require one. In the present day, many devoted SiC drivers supply handy options like unfavorable gate drive, DESAT, OCP, OTP and different protections. Choosing the best gate driver makes driving a SiC system no tougher than driving a silicon MOSFET.
The place the Prices Are
There’s a misperception that SiC options are costly. In comparison with silicon MOSFET, there’s a small value premium for a SiC system; nevertheless, contemplate a typical silicon-based 30 kW energy answer. Right here, 90% of the general value is discovered within the inductors and capacitors (60% and 30%, respectively), with the semiconductor units representing solely 10% of the general invoice of supplies (BOM) value. Suppose the silicon MOSFETs are changed with SiC switches. In that case, capacitance and inductance dimension might be diminished by 75%, which delivers a major value discount (in addition to dimension discount), outweighing the fee improve within the switching elements. Moreover, silicon units supply decrease effectivity than SiC, requiring costly and ponderous warmth sink options. Because of this, the full BOM value of a SiC answer is decrease than a silicon equal.
The SiC ecosystem is evolving quickly as know-how enters the mainstream. There’s now a large alternative of commercially obtainable SiC units and related gate drivers in a number of packaging types to swimsuit a number of purposes. The information base for SiC is growing all through the trade as producers improve their help via purposes engineering groups, reference designs, software notes, simulation fashions and instruments. Element availability (not simply SiC) has lately been a difficulty for some sectors.
Nevertheless, following the current acquisition of GTAT, onsemi’s provide chain is way n functionality, together with quantity boule development, substrate, epitaxy, system fabrication, best-in-class built-in modules and discrete bundle options. To help the anticipated development in SiC over the subsequent few years, onsemi plans to extend the capability of substrate operations fivefold and make substantial investments in increasing the corporate’s system and module capability to double it throughout all websites by 2023. That might be adopted by practically doubling capability by 2024, with the power to develop once more as required.
Fig. 2. onsemi’s end-to-end provide chain for silicon carbide.
Robustness at Excessive Temps and Voltages
The large bandgap (WBG) of SiC materials supplies it with higher avalanche ruggedness inside SiC MOSFETs, because the thermally generated service focus is way smaller than that of silicon units. Whereas it’s true that SiC units have smaller geometries, so their quick circuit stand up to time is decrease than that of an IGBT, nevertheless, utilizing an acceptable SiC gate driver ensures that the fault is detected and system is turned-off with loads of margin to spare, to allow them to be used with confidence in purposes the place robustness is required. The battery voltage on many EVs is transferring from 400 V to 800 V or 1,000 V. Inside photo voltaic photovoltaic (PV) programs, the enter voltage is growing from 600 V to 1500 V.
To fulfill this requirement for units with increased breakdown voltages, onsemi has developed a variety of 1700V M1 planar EliteSiC MOSFET units optimized for quick switching purposes. Alongside these MOSFETs, it has additionally launched a variety of 1700 V SiC Schottky diodes.
Fig. 3. 1700V M1 planar EliteSiC MOSFET
The Backside Line
Having checked out silicon and silicon carbide units throughout numerous metrics, it’s clear many widespread misconceptions don’t have any factual foundation, and engineers needs to be assured about choosing and making use of this versatile know-how of their designs.
