> Unfortunately I have no control over which power supply
> will be used though they will be 24 volt supplies. My main concern in ter=
ms of
> protection is if the load is short circuited. This could happen when the =
PWM is
> anywhere from 0 to 100% .  I have looked at a few techniques.

Well, the obvious step one here is have the supply for your micro diode iso=
lated from where the LED supply goes, so that in the event of the LEDs goin=
g short circuit and pulling the supply down the power for your micro doesn'=
t get pulled down with it.

Now after the diode you have a good sized capacitor (I'd look in the 200-47=
0uF range) and a switching regulator down to 5V/3.3v for your control elect=
ronics. There are a number of switchers around now from National semiconduc=
tor/TI and Linear Technology designed for automotive use with 60V input rat=
ings that fit the bill here.

By keeping your control electronics running in this manner you can now deal=
 with the LED problem.

To detect the LED problem you can probably use a PCB track as your sense re=
sistor and a high side current sense chip, available from a number of sourc=
es including Analog Devices, Microchip and Linear Technology. Should be som=
ewhat cheaper than the hall effect devices you mentioned.



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