Vf varies a bit from 1.2 V typical @ If = 10 mA, down to 1.0 V typical @ If =
0.3 mA. You’d think these things would last forever given the absolute max If
is 30 mA.
Interesting point though. I didn’t look to see which one has the max frequency
or possibly time of use. I would guess it would depend somewhat on what
particular configuration is being used.
Ken K6MR
From: David Gilbert<mailto:ab7echo@gmail.com>
Sent: Thursday, June 10, 2021 05:15
To: cq-contest@contesting.com<mailto:cq-contest@contesting.com>
Subject: Re: [CQ-Contest] Mk2R+ optocouplers
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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