> On Thu, Jan 29, 2015 at 6:09 AM, IVP wrote: > > That load is starting to get up there, compared with the original > > 5V 1A. It's not going to be a reactive load, like a motor, so you > > shouldn't be troubled by too much noise > > > > I think it would be prudent to add the driver to get the gate on > > and off quickly, as the PIC can supply only 25mA. For the small > > load (5W) that won't matter so much, as wattage across the FET > > is easily dissipated by the package. When the load is a potential > > 192W then you will need to consider the time spent in the linear > > region, and it should be as short as possible >=20 > That makes sense. That's sort of what my original concern was, though > I realize I didn't ask the question very well. >=20 > Is there a way to calculate how much power I will be dissipating in > the FET package? I'm trying to figure out how much of a heatsink I > might potentially need. >=20 > Josh > --=20 The capacitance on the gate and the available current from the driver will= =20 determine how long the transistor will spend in the linear reqion. More cur= rent=20 and the capacitor will be charged/discharged quicker. The same with lower=20 capacitance. Higher frequency also means that you will spend more time in t= he=20 linear region. Mostly a fet for higher voltage and current have more gate capacitance. So= =20 don't choose a fet that is way larger (in terms of voltage and current) tha= n=20 you need since you will have to drive it harder to get the same dissipation= as=20 for a smaller fet. /Ruben --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .