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is an optocoupler faster rise time than a transistor?

ratstar

Aug 20, 2018
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When you want to make a gigahert oscillator, I see on the internet that transistors only rise in megahertz not gigahertz. (But that could be bulldust... oc)
But I was wondering what the switching speed of optocouplers would be? It could be faster.

So its an led, next to a photovoltaic cell, and it depends on them both being able to be quick - anyone can help me here?
 

Harald Kapp

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I see on the internet that transistors only rise in megahertz not gigahertz
Nonsense. We've had this discussion before: it depends on the transistor used.

It could be faster.
It could, but it definitely isn't. Don't "wonder", look up datasheet(s). Read e.g. this treatise.
And even if it were: how would you drive the input side of such an optocoupler if there a no transistors fast enough, as you erroneously think?
 

Harald Kapp

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And which component would drive this other optocoupler? Another optocoupler? And so on...
 

ratstar

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It finishes off with the direct battery connection. (You can make an oscillator with opto-couplers.)

 

Nanren888

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Been a while since I've used optoisiolators seriously, but I do remember reservations about their speed. I presume it was something to do with their capacitance somewhere. Anyway, there will be some compromise between speed and power, two of your previous themes. If you lower the resistor values to get speed, it will cost you current.
Sort of reminds of the joule thief blocking oscillator.
 

ratstar

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I dont think the speed problem is the LED, its the photovoltaic cell, you need 1ns!
 
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