Author Topic: Optocoupler question  (Read 525 times)

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Offline otterTopic starter

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Optocoupler question
« on: June 18, 2020, 09:47:13 am »
How do I read out the Vce from the datasheet below, if I use If=8mA and Ic=120mA?
https://www.onsemi.com/pub/Collateral/MOCD223M-D.PDF

 

Offline magic

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Re: Optocoupler question
« Reply #1 on: June 18, 2020, 09:57:30 am »
You can't. Current transfer ratio is only 500% guaranteed and 1000% typical, which means 5x or 10x more Ic than If.

See figure 4. With If=10mA you only get a few times more Ic than with If=1mA, which would be 10mA typical. You could increase collector current by applying even more than 5V while the optocoupler is turned on but come on.
 

Online moffy

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Re: Optocoupler question
« Reply #2 on: June 18, 2020, 09:58:11 am »
The current transfer ratio is min:= 5x, typ:= 10x with Vce = 5v. Therefore with If = 8ma, the CTR falls off a bit so lets say about 35ma is the maximum output current you could rely on at 25C.
« Last Edit: June 18, 2020, 09:59:49 am by moffy »
 

Offline Ian.M

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Re: Optocoupler question
« Reply #3 on: June 18, 2020, 10:21:44 am »
Its worse than that as the O.P's linked datasheet doesn't include any operating lifespan or reliability data.  As LED light output is well known* to degrade over the LED's operating life, it would be foolish to design with less than a factor of two margin, i.e. about 17mA Ic, if you want it to have a reasonable chance of reaching 10000 operating hours without failure.  If its on all the time 10000 hours is barely enough to outlast a one year warranty!

* e.g. https://www.vishay.com/doc?49267   
 

Offline otterTopic starter

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Re: Optocoupler question
« Reply #4 on: June 18, 2020, 11:00:47 am »
If I use the this part instead (new link below), it seems I can get 120-140mA with Vce=1V with If=5mA.
What can be expected if I increase If to 10mA?
Do I need the selection "K" to get this results?

I will consider deratig.

https://www.mouser.se/datasheet/2/698/PN10235EJ04V0DS-1528581.pdf
 

Offline magic

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Re: Optocoupler question
« Reply #5 on: June 18, 2020, 11:05:13 am »
Use the optocoupler to drive some 2N2222 if possible. They aren't really meant to control high current by themselves.
Alternatively, some kind of opto-mos, solid state realy, that kind of stuff.
 
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