The ideal diode, with low VF and negligible switching losses, has a Schottky structure.
However, such a diode is limited to voltages below 200V with silicon substrates.
Alternatively silicon carbide (SiC) wafers enable higher voltage ratings of up to 1200V to be reached.
The produced device exhibits negligible switching losses, resulting in higher efficiency and lower radiated & conducted noise in the application. |
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Improved recovery and forward voltage drop
Silicon carbide structured diodes exhibit a tiny dynamic reverse recovery current, only linked to the junction capacitance. Furthermore, this current remains stable when the junction temperature varies. In bipolar silicon diodes, the main physical effect is due to the minority carriers, which significantly increase both reverse recovery current (IRM) and charges (Qrr). For this type of diode, the value of the IRM is doubled, and Qrr is multiplied by a factor four when the diode heats up from an operating junction temperature of 25°C to 125°C.
Besides the clear improvement in dynamic characteristics, the forward voltage drop at high temperature and nominal forward current of a SiC diode is 10% lower than that of the Tandem diode STTH806DTI, its closest silicon bipolar competitor on the market.
The combination of a better static characteristic on the VF, and better dynamic characteristics with the Qrr (called Qc for SiC, since it is limited to a capacitive current), bring improved efficiency and thermal performance to their applications.
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Benefits Applications
The converter efficiency is the first improvement factor for the application. Trials have shown improvements in the order of 0.5% to 1%, especially at low load and high frequency.
The second direct improvement is the power density allowed by the SiC diode, for two reasons:
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Its dynamic characteristics allow the switching frequency to be doubled without degrading the switching losses. The inductors will be reduced in consequence.
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The EMI, due to the soft behaviour of the SiC diode on to off state, are reduced. So are the mains filter and snubber circuits that are usually dimensioned to reduce the EMI.
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