Dale Botkin wrote:
.........
>> Understood - still gives me the willies, as I like to build in some
>> kind of basic "guarantee", at the level below the uC. Some of us
>> like to live our lives a little further from the edge ;-).
>
>Sure thing...  if you've got any bright ideas I'm open to suggestions.  15
>rows of LEDs, 16 LEDs per row, variable brightness, and they've got to be
>fairly bright when cranked up.  Other than dissipating a boatload of power
>at the transistors or somewhere else (oh, did I mention limited space and
>a harsh environment?) I couldn't come up with an acceptable alternative.
>

Dale, just a couple of thoughts. I would hate to rely upon the uC
putting out a specific duty cycle as the primary means to keep a
system like this from smoking. Other possibilities [maybe you have
these implemented or they are not feasible, given your particular
reqs]:

- fuses, or better yet [I think] polyswitch resettable fuses.
- arranging the loads on the drivers [MOSFETs, ULN, ...] so that
  the driver could not run an excessive current through the LEDs;
  ie, configure LEDs in series columns and parallel rows - although
  this may overload the driver in normal ops.
- adding a small R [say 0.1 ohm] in series with the power source to
  sample load current, and feeding to an independent shutdown ckt
  [separate from the uC]; this should only add a few components and
  could save a lot.

best regards,
- dan michaels
www.oricomtech.com
========================

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