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Silicon Carbide FETs Shine in SMPS Applications

Silicon Carbide (SiC) FETs are starting to gain traction in markets where the inherent efficiency of PWM (pulse width modulation) and SMPS (switch mode power supply) systems is already an advantage. Some of the key players in this new technology showcase power systems that are significantly more efficient than preceding IGBT and conventional MOSFET designs. In locations like Hawaii where electricity can cost more than $0.35/kWh, this becomes important. There are similar high power-costs to deal with in locations in Europe and Asia. It's also important for anyone living off of the grid.

Power systems that use SiC devices as the switching element can be up to 6 percent more efficient. They can generally withstand higher junction temperatures than conventional power systems.

SiC FETs are different in their gate drive performance requirements than conventional IGBT and MOSFET solutions. The SiC devices can require a greater than 20 V positive bias to fully enhance (turn on) the conduction channel. They also usually need a negative bias to fully deplete (shut off) if they are operating at high temperatures. In this way, they are neither simply enhancement-mode nor depletion-mode devices. Instead, they are a bit of both.

Beyond the gate-biasing considerations, SiC FETS offer advantages in spite of their higher (but rapidly dropping) initial cost. As of early in the year, the devices were running about 2.5 times the cost of an IGBT of similar current-handling capability. This cost differential may not matter that much when the entire MLB (materials, labor, and burden) is considered. The efficiency savings (mentioned above) will also help pay back the higher MLB costs. Even at $0.15/kWh one might save close to $0.08/hour on something that is sized for 10 kW total power.

Over the years this can add up significantly. Given a 10-year lifespan, this can amount to over $8k in savings of electricity costs on something required to run 24 hours a day, seven days a week, 52 weeks per year. Consider also that the higher peak-temperature capability of these parts can mean less downtime. That results in additional savings.

Some of the emerging players in this market include Cree, Microsemi, and Powerex. Some of these devices are regularly stocked by Digikey, Mouser, and other large distributors. This implies the devices have reached commodity status.

The devices also allow a much faster switching frequency in the systems, reducing the value of inductance needed in filter circuits. This means additional savings in this area, due to a reduction in materials required for the inductor and in the corresponding PC board area. Note that EMI (electromagnetic interference) could present issues at these higher switching frequencies, so this is an area where added precautions are recommended.

Applications include a variety of power equipment or subsystems: solar inverters (aka micro inverters for photovoltaic arrays), power factor correction (PFC) circuits, PWM motor drives or controllers, and many different topologies of SMPS.

Do you see any of these devices in your product's future? What do you see as the potential uses of these parts? Are there any disadvantages with respect to your designs?

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10 comments on “Silicon Carbide FETs Shine in SMPS Applications

  1. samicksha
    September 28, 2013

    I agree that  SiC is a better power semiconductor, but i am still not sure if their claim of no tail current during switching is true and up to the date…

  2. BillWM
    September 28, 2013

    The devices I tested last winter from Cree had very low tail current and leakage up to 125C Tj — It is above this temperature that one needs the negative bias to get them shut off.   The bias circuit is key to this parameter.

  3. SunitaT
    October 29, 2013

    Switched-mode power supplies have solicitations in various zones. A switched-mode resource is chosen for an app when its efficiency, size, weight or wide input range tolerance make this preferable to linear power supplies. Primarily the cost of semiconductors made switch-mode provisions a premium cost substitute, but current manufacture switch-mode provisions are nearly always worse in cost than the corresponding linear power supply.

  4. jack90
    March 8, 2014

    Silicon carbide, similarly renowned as carborundum, is a amalgamate of silicon moreover coal along chemical plan SiC. It arrives in quality as the exceedingly uncommon turquoise moissanite. Grains of silicon carbide can be bonded unison by sintering to compose mere firm clays that are far worn in diligences requiring shrill stamina, such as automobile stops.

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