Components

600V Super Junction MOSFETs Claim Fastest Reverse Recovery Time

Rohm introduced its new PrestoMOS™ Series of 600V super junction MOSFETs, the R60xxJNx series. According to Rohm, this series, which includes 30 models, increases design flexibility while maintaining the industry’s fastest reverse recovery time (trr). Presto’ is an Italian musical term meaning ‘very fast’. So the appropriately named MOSFETs, in addition to having a very fast trr, offer high switching speed.

The company optimized the R60xxJNx series for EV charging stations and motor drive in home appliances such as refrigerators and air conditioners (ACs).

Some estimates say that about 50% of the total power demand worldwide is used to drive motors, Rohm noted. With the continued spread of electrical appliances in emerging and developing countries, this percentage is forecast to only increase, the company says.

IGBTs are frequently used as switching elements in inverters that drive motors in home appliances including refrigerators and air conditioners.

Recent trends of improving energy savings has inspired the demand for MOSFETs with reduced power consumption during steady state operation. To meet this need, Rohm first launched the PrestoMOS™ series of power MOSFETs in 2012.

According to Rohm, the PrestoMOS series features the industry’s fastest reverse recovery time, resulting in lower power consumption. As with its conventional products, this new series employs Rohm’s proprietary lifetime control technology to achieve ultra-fast trr. This enables a reduction in the power loss of approximately 58% at light loads compared with IGBT implementations.

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Additionally, increasing the reference voltage needed to turn on the MOSFET prevents self turn-on, which is one of the primary causes of loss.

Moreover, optimizing the characteristics of the built-in diode allowed Rohm to improve the soft-recovery index that is specific to super junction MOSFETs. The improved soft recovery index reduces noise that can lead to malfunctions.

Rohm asserts that eliminating these barriers to circuit optimization gives customers greater design flexibility.

In relatively low current conditions, the MOSFETs provide advantages such as high switching speed and low conduction loss. For example, in air conditioners, they are more effective than an IGBT in reducing power consumption during steady state operation.

Keys to Improving Design Flexibility

Switching speed increase, self turn-on, and noise generation are conflicting phenomena, thereby making it necessary to optimize circuitry by adjusting the gate resistance and other factors during circuit design. Unlike general-purpose MOSFETs, Rohm’s R60xxJNx series takes measures against noise and self turn-on, giving customers a great degree of design freedom.

Implementing self turn-ON countermeasures minimize loss

Optimizing the parasitic capacitance inherent within the MOSFET structure allowed Rohm to reduce the unintended gate voltage during switching by 20%.

Also, the specialized design makes it difficult for self turn-on to occur because they increased the threshold voltage (Vth) necessary for turning ON the MOSFET by 1.5x. This increase expands the loss adjustment range due to gate resistance and other factors.

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Improving recovery characteristics reduces noise

Generally, the super junction MOSFET’s internal diode shows hard recovery. However, by optimizing the internal structure, Rohm’s R60xxJNx series can improve the soft recovery index by 30% compared to conventional products and successfully reduce noise while maintaining the industry’s fastest reverse recovery time (trr).

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This improved soft recovery index makes it easy for customers to adjust noise such as the noise that results from gate resistance for example.

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