MOSFETs enables energy savings for inverters in AC systems

23rd April 2019
Alex Lynn

A new lineup of its PrestoMOSTM series of 600V super junction MOSFETs that includes 30 new models, has been announced by ROHM. This series increases design flexibility while maintaining the industry’s fastest reverse recovery time (trr) optimised for EV charging stations and motor drive in home appliances such as refrigerators and Air Conditioners (ACs).

Reports show that close to 50% of the total power demand worldwide is used to drive motors, and with the continued spread of electrical appliances in emerging and developing countries, this percentage is expected to only increase.

IGBTs are commonly used as switching elements in inverters that drive motors in home appliances such as refrigerators and ACs. Recent trends towards improving energy savings has driven the demand in a variety of applications for MOSFETs with reduced power consumption during steady state operation.

To meet this need, ROHM launched the PrestoMOSTM series of power MOSFETs in 2012. This series features the industry's fastest reverse recovery characteristics, achieving lower power consumption. As with our conventional products, this new series leverages our proprietary lifetime control technology to achieve ultra-fast trr. This enables a reduction in power loss of about 58% at light loads when compared with IGBT implementations.

Additionally, raising the reference voltage needed to turn ON the MOSFET prevents self turn-ON, which is one of the main causes of loss. Furthermore, optimising the characteristics of the built-in diode allowed us to improve the soft recovery index specific to super junction MOSFETs, which reduces noise that can lead to malfunctions. Eliminating these barriers to circuit optimisation provides customers with greater design flexibility.

What is PrestoMOSTM?
‘Presto’ is an Italian musical term meaning ‘very fast’. MOSFETs provide advantages such as high switching speed and low conduction loss in the relatively low current condition. For example, in the case of air conditioners they are more effective than IGBT in reducing power consumption during steady state operation. 

PrestoMOSTM is ROHM’s power MOSFET which body diode is characterised by the industry’s fastest reverse recovery time (trr) that contributes to lower power consumption in inverter applications.

Improving design flexibility
Switching speed increase, self turn-ON, and noise generation are conflicting phenomena, making it necessary for customers to optimise 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, providing customers a great degree of design freedom.

Implementing self turn-ON countermeasures minimise loss
Optimising the parasitic capacitance inherent within the MOSFET structure allowed us to reduce unintended gate voltage during switching by 20%. In addition, the specialised design makes it difficult for self turn-ON to occur by increasing the threshold voltage (Vth) necessary for turning ON the MOSFET by 1.5x.

This expands the loss adjustment range due to gate resistance and other factors implemented by the customer.

Improving recovery characteristics reduces noise
Generally, the recovery characteristics of the super junction MOSFET’s internal diode shows hard recovery. However, by optimising the internal structure, ROHM’s R60xxJNx series is able to improve the soft recovery index by 30% over conventional products and succeed in reducing noise while maintaining the industry’s fastest reverse recovery time (trr).

This makes it easy for customers to adjust noise (i.e. due to gate resistance).


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