High performance MOSFETs build better power tools

High performance MOSFETs build better power tools

Cordless power tool designers face multiple challenges, many of which interact and, in some cases, compete with each other making component selection critical to producing a winning design.

The battery itself is one of the most obvious trade-offs. Selecting a battery with the most energy per unit weight is key; more important is to ensure that all aspects of the design are as efficient as possible so as not to waste energy.

Even in normal use, particularly tight nuts or a jamming drill will demand peaks of current to deliver the requisite torque.

Control and protection circuitry must ensure that the battery does not deliver so much instantaneous power that the electronics or motor are damaged.

Temperature is another challenge; improving efficiency allows the tool to run cooler and, therefore, work at higher ambient temperatures.

A tool that is not working could mean a critical safety job is delayed. A failed tool will damage the reputation of the manufacturer, meaning that reliability and robustness are high on the agenda of all cordless power tool designers.

Trench LV MOSFETs from Toshiba Electronics Europe (TEE) are a recent technology specifically aimed at cordless power tool design. U-MOS VIII MOSFET technology offers a broad product range of 30-250V class MOSFETs. The latest U-MOS IX-H technology supports 30-60V class MOSFETs with RDS(ON)max values as low as 2.3mΩ in the 3mm x 3mm 40V package, while the 5mm x 6mm 40V package drops values to 0.85mΩ.

In developing U-MOS technology, TEE focused on three main parameters affecting power switching losses; gate charge (Qg), on-Resistance (RDS(ON)) and recovery charge (Qrr - sometimes Qoss/Eoss). The gate charge and recovery charge have the greatest impact in high-speed applications while high values of RDS(ON) generate waste heat while the MOSFET is conducting current.

The U-MOS range offers several performance levels and combinations of these critical parameters, allowing designers to select the most appropriate for their particular application. The range will be further broadened with the future introduction of 100V and 80V devices.

Toshiba has developed a white paper that discusses cordless power tool design in detail. To download it click here:

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