Help Finding Regulator: 1501A50

Thanks Win

As always you were helpful

Thanks, you're too kind! I try to be helpful, but sometimes I'm not so sure.

I pointed out problems with the AP1501A buck converter: too much voltage drop, too much dissipation at high currents. Thinking about the O.P.'s failure, yes the part has current limiting (at 6A) and thermal limiting (probably at about 150"C), but this can't insure long life. In fact the part is allowed to operate in a region where it'll almost certainly suffer severe life-shortening stress.

If I was being really helpful, I would have found a similar buck converter in a TO-220 package, with more-effective MOSFET switches, and hopefully with the same pinout, that could serve as a more reliable replacement. But finding such a beast is more like real work, and I was lazy.

The only simple suggestion that occurs to me is to use the lower-current AP1501 version rather than the AP1501A. Both types have a similar switch saturation voltage, about 1.25V at say 2A, which is a safer operating region, and they both have the same thermal resistance, Θ_JC = 5"C/W. But the AP1501 version current limits at 4A rather than 6A, and that should be safer for the part under fault conditions. A second suggestion would be to beef up the part's heat sink. At 40% duty cycle it'll still be dissipating 1.0W at 2A, and 1.7W at 3A. And of course the O.P. should check his 5V circuit's current drain, and make sure it's reasonably low.