>> In this case I didn't do my homework beforehand, and Olin's concern about the instantaneous power dissipation in the MOSFETs is a very realistic one. It's an issue that should be addressed before proceeding with any sort of "ramped gate drive" soft-start scheme such as the one I proposed. << Dave, I didn't say (and certainly didn't mean) that the soft start design was bad, only that I personally didn't like it. What bothers me most is how the FETs will be taking pulses of serious power. Even if it can be proven that everything stays within current, power, and temperature ratings, I don't like the sudden thermal stress. In the long run, this has got to have *some* effect. Maybe it will only lower the expected life from an irrelevantly large number to a slightly smaller irrelevantly large number. There is also the issue of what if the bulbs get changed or more get added in the future. Again, this isn't based on defensible numbers, just instinct. Others could legitimately argue I'm being silly. I certainly haven't done homework on this either, so here are some rough calculations. I'm making this up as I'm typing. I remember something about 7A steady state. Let's say the initial current is 70A at full voltage. If the FETs were 1/2 on with cold bulbs (it won't happen like this, I'm just trying to pick something to see where it leads), that would be 35A x 60V = 2100 watts. If this happened for 20mS, that would be 42W averaged over 1 second. Hmm. I think this is saying that this very crude model doesn't provide conclusive evidence on way or the other, but that a much more realistic model needs to be properly worked thru to prove this is OK before implementing it. That fact that it is close enough to require more detailed calculations makes me nervous about this method again. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, olin@embedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.