I am following the design schematic of a MIDI controlled synthesiser and am currently trying to figure out the design process.

An forward inout current "If" of 5mA is used. MIDI standards state that a high speed optocoupler with 2us or less is required. And in this design an 6N139 is used. From what I can see from the datasheet, it only shows the speed at 2 input forward currents:

At If = 0.5mA: Typ Rise Time = 13.6us
Typ Fall Time = 2.5us

At If = 12mA: Typ Rise Time = 1.3us
Typ Fall Time = 0.24us

I can't seem to find any graph or information regarding what rise and fall times I would expect at 5mA. would the 6N139 be sufficient to provide 2us at 5mA? The project is a copy so it does work but I am just trying to understand why this component would have been chosen

http://www.farnell.com/datasheets/1...TBglSQhFOfyLaGfN6A85fFF2qHX36wTxoCdRgQAvD_BwE

 

Where exactly in the data sheet did you find that rise and fall time info?

 

Where exactly in the data sheet did you find that rise and fall time info?

In the datasheet. duh! (page 4 )

 

it only shows the speed at 2 input forward currents:

Note that these figures are also at vastly different Rl, which will mostly affect turn-off time (at least I think it should). Imagine the optocoupler as this: diode current is multiplied by some constant, which charges a capacitance. From this capacitance a transistor is controlled. Now I am not so sure how the Rl relates to the switching time, but I think some muller capacitance will be hidden in that and it will have an effect, even though the capacitance is hidden behind a darlington pair.

 

In the datasheet. duh! (page 4 )

Those values are not given on page 4 of the data sheet he posted.
Care to try again? duh!

 

Oh crap, the numbers got somehow jumbled up and through my short memory they seemed to fit in the correct timeframe as I was jumping between the forum and the datasheet

 

Apologies, those values were found in this datasheet. Same model number but different brand:

https://www.vishay.com/docs/83605/6n138.pdf

It is actually the first datasheet that I am working with. Is there a way to obtain the rise/fall time from the propogation delay in this case ? I just need to show that it is around or below the required 2us for 5mA IF

 

Apologies, those values were found in this datasheet. Same model number but different brand:

Sorry, I don't see it in that data sheet either.

 

MIDI standards state that a high speed optocoupler with 2us or less is required.

2μs what?
Is that rise/fall time or delay time, or a combination of both?

 

It is rise/fall time, 2us in order to keep up with serial MIDI