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  • I decided to bite the bullet and get SMT parts. The specs on the VNP49N04 didn't really inspire confidence in their performance at 3.3v gate voltage.

    I got some DMN2075U's and some Si2302CDS's (dirt cheap from china). I just got the DMN2075U's, and my god those things are tiny. It boggles my mind that these mosfets smaller than a grain of rice are rated at 4.2A continuous current.

    I'm going to use these for my LED drivers (max current 1.1A). I'll thermal-epoxy them to the case (a nice thick hunk of metal) for cooling.

    Now - any recommendations for P-Channel mosfets? (presumably we're talking more surface mount stuff?)
    Is there anything like the inverse of a ULN2803 (ie, to pull up instead of down)?

    Pinball machines use the ULN2803's to drive the columns of the switch matrix. The columns are nominally pulled up to 12v, and the MCU drives a shift register that drives a ULN2803 to pulse columns low while monitoring the rows. How the hell do they blow like that? Generally because +20 or +50v gets briefly shorted to a switch wire. This is often non-trivial to track down - tales abound of people spending days searching for the intermittent short. Personally, I had one case where a metal ramp was electrified (at +50v - guess how I discovered that?) because the orientation tab had broken off a solonoid, allowing the terminal to contact the mounting bracket. But it only blew switches when you missed a shot to that ramp, causing the ball to roll back down and graze the side of a standup target switch, connecting the switch to the ramp and blowing the column driver...


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