SDG #273 MOSFETs, Gate Drivers and PWM Driver Design

This is a design walkthrough rather than a product review, following the reasoning behind a PWM load driver board from a blank page through to sending files for fabrication. The starting point is a set of real requirements: voltage rating with headroom, continuous current, and switching frequency, because those three figures dictate almost everything that follows in part selection.

The practical value is in the parametric search workflow. Rather than choosing a familiar part number out of habit, the selection is narrowed using distributor filters on voltage, current, package and on resistance, then verified against the datasheet. Attention is paid to the parameters that are routinely overlooked: RDS(on) quoted at a realistic gate voltage rather than the headline 10 V figure, safe operating area and thermal limits versus the optimistic pulsed current figure, and the difference between what a device can survive and what it can do continuously on a modest PCB copper area.

Gate drive receives the most attention, and rightly so. Input capacitance and total gate charge are translated into the peak current a driver has to supply to switch the device in a sensible time, which is what keeps switching losses and device temperature under control. That figure then becomes the search criterion for the gate driver itself, alongside supply voltage range, propagation delay and package.

The closing sections cover the schematic, decoupling and gate resistor choices, then layout: keeping the gate loop tight, giving the drain and source paths adequate copper, and specifying board thickness and copper weight when ordering. The episode is relevant to anyone whose MOSFET circuits run hotter than the calculations suggested they should.