Electronics > Projects, Designs, and Technical Stuff
Switching mosfet in leaded package faster than 1000 A/µs ?
T3sl4co1l:
--- Quote from: langwadt on August 26, 2019, 04:19:57 pm ---
--- Quote from: T3sl4co1l on August 24, 2019, 08:49:04 pm ---SMT components perform better (D2PAK has about half the stray inductance of TO-220)
--- End quote ---
how is that, just from mounting alone? isn't D2PAK just a TO-220 with a leg and tap chopped off?
--- End quote ---
Precisely. Inductance is length.
Tim
langwadt:
--- Quote from: T3sl4co1l on August 26, 2019, 10:51:44 pm ---
--- Quote from: langwadt on August 26, 2019, 04:19:57 pm ---
--- Quote from: T3sl4co1l on August 24, 2019, 08:49:04 pm ---SMT components perform better (D2PAK has about half the stray inductance of TO-220)
--- End quote ---
how is that, just from mounting alone? isn't D2PAK just a TO-220 with a leg and tap chopped off?
--- End quote ---
Precisely. Inductance is length.
Tim
--- End quote ---
but you don't have to have a to-220 flop around in the breeze, you can mount is pretty much like a D2PAK
T3sl4co1l:
You can, but when do you get the chance to do that?...
This by the way is an ST part, nickel plated tab, so it tinned very poorly. :(
That's one obstacle already; not hard to find tin-plated tabs, but then you need to make sure they're always purchased as such, and find another in case the manufacturer changes it.
But now you can't heatsink it! At least, not as easily.
You're not required to need some "flopping in the breeze" for heatsink mounting, but it is more likely. A lot of vertical heatsinks are designed to hold the body at full lead length, these for example: https://www.digikey.com/product-detail/en/ohmite/C220-075-3VE/C220-075-3VE-ND/2764652
Custom ordered, or done by hand, you can specify exactly the right board-to-mounting-hole distance, but your off-the-shelf selection is more limited.
Or you might mount the devices underneath the board (legs poking up), in which case lead length is dictated by lead form and board standoff height. Which actually, if all the devices are the same thickness, you can even use the board itself as the tension clamp, and avoid needing mounting screws at all (and the ills that come with them: uneven clamping force). Or if the board itself is dissipating power (say, snubber resistors, filter chokes/caps), just keep going and make a clamped sandwich of two heatsinks, a big soft thermal pad, PCB, transistors and a thin thermal pad. (I want to do that some day, I just haven't had an application for it yet. :) )
Or you could mount the board parallel with the leads, and hook the leads into holes right near the board edge. Or make full-body cutouts. Or surface mount them -- I've actually seen that in a car amp, bodies clamped to heatsink, leads surface mounted, just sticking straight out over the board, lap soldered. Not that it needed it, but apparently it just worked out that way. That would be really good.
So yeah, absolutely; but if you need closer to an order-of-magnitude reduction, you're still looking at many devices in parallel, or flatter devices.
Tim
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