Thanks. As I see it, you can always specify an antiparallel diode to protect an LED from reverse voltage, and know that it will do that. If it doesn't, there has to be a defect somewhere.
But as I see it, a series diode can also give that reverse polarity protection, provided you consider the whole circuit. I don't know about "guarantee", but if the 1N4004 datasheet is to be believed, the maximum reverse voltage in this circuit will be about half a volt - less than a diode drop - and that's at Tj 100C. If the ambient raises the diode to 100C, there well may be a problem that should be solved elsewhere. The ~ 12 mA forward through the diode is certainly not the culprit that raises it to
100C.The use of an antiparallel diode can only exacerbate a heat problem as it protects the LED - and likely with a higher reverse voltage! (I'm gonna have to measure the Vf across a
1N4004 at about 12 mA - the datasheet does not show it below 100 mA.)Maybe it's a case of this: you can always throw a diode across the LED antiparallel to provide reverse polarity protection, but if you use a series diode, you must look at the datasheet and compute the results to be sure it will provide that protection. I dunno.
I did not top post. Go read it again.
Ed