I was kind of sloppy there. Given the Vf of an infrared LED, the drive
current would be less than 4 milliamps.
73,
Dave AB7E
On 6/8/2021 11:30 PM, David Gilbert wrote:
Yeah, that would be 5 milliamps for all of them, which certainly is
not an excessive amount of drive current. Most application notes for
optocouplers tended to spec about 10 milliamps for a typical
application, and as best I can remember 50 milliamps was often the max
rating. If those optocouplers were degrading at 5 milliamps they
really had poor quality LEDs in them.
I still don't buy the idea that the lower speed slots should make much
difference, though. I can't think of any reason why speed should make
a difference in LED lifetime at 5 milliamps unless those slots simply
were activated significantly more often ... higher duty cycle, not
higher speed.
73,
Dave AB7E
On 6/8/2021 10:19 PM, Ken K6MR wrote:
From the info I have it looks like they are all driven through a 1k
resistor, supply voltage is either the USB 5V bus or the system 5V
bus. Drive current looks to be well below the max shown on the data
sheet.
My unit is pretty old and has all Fairchild (white devices).
Ken K6MR
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