[CQ-Contest] Mk2R+ optocouplers

[David Gilbert]

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
>>