Finding the optimal power switching solution for cordless handheld tools

Finding the optimal power switching solution for cordless handheld tools

Power tools have simplified the lives of professional tradespeople and craftspeople providing accurate and fast operation that is significantly less demanding on the human body than their manual alternatives. With the advent of powerful, compact and long-lasting battery technology, portable power tools have enabled work, maintenance and repairs to be undertaken almost anywhere. Consumers with a hand for DIY have also benefitted, with many power tool manufacturers providing innovative, value-for-money solutions with interchangeable battery packs.

The architecture of all cordless tools follows the same basic approach regardless of function. The power element is delivered by a motor and its control electronics, often utilizing the efficiencies offered by brushless DC (BLDC) motors. Power is supplied via a rechargeable battery pack, with energy being stored in Lithium-Ion batteries watched over by a battery management system. Finally, restorative charge is supplied by an AC/DC adapter, delivering a suitable charging voltage from the household mains supply.

What all these system blocks have in common are power switches, such as MOSFETs, which control power delivery in conjunction with matching control circuitry. With power tools often being used and carried for long stretches, several requirements drop out that impact the MOSFET selection. Efficiency, which also impacts heat generation, is high on the list. Also, in order to develop tool that lies comfortably in the hand, devices need to be selected whose packaging enables the desired form factor.

The latest generation of low-voltage U-MOS IX-H MOSFETs from Toshiba tackle these requirements, starting with the key parameters that impact power losses in switching applications; gate charge (Qg), on-resistance (RDS(ON)) and recovery charge (known as Qrr, Qoss or Eoss). This has led to best-in-class Qvs RDS(ON) along with improvements in recovery charge that typically adversely impact EMI and, occasionally, can lead to errors in current monitoring measurements. These improvements over previous generation devices help deliver smoother motor control and extend battery life to power tools.

Packaging is also a critical element in the component selection process, both from the aspect of manufacturability as well as implementing a suitable heat dissipation strategy. The new DSOP Advance package is a dual-inline surface mount package that integrates a metal slug in the upward facing surface. Topside thermal resistance, channel to case, can be as low as 0.93°C/W combined with a low 0.88°C/W on the bottom side via the metal frame (Tc = 25°c). Such packaging advancements enable power tool developers to offer innovative form factors, as well as compact charging solutions and batteries.

To find out more about low-voltage U-MOS IX-H MOSFETS and how they support innovative cordless products, take a look at our white paper available here:

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