Re: optocoupler trouble



ted wrote:

You should check the maximum diode current, too -- that 10mA is
certainly suggestive of what you ought to be able to do. Figure 10mA
in, 2mA out, means you'll need to use at least a 2500 ohm resistor to
pull the collector all the way down.

Thanks, and would you please explain why 2500 ohm is the correct
resistance, indeed why the resistance at that point makes any
difference to what the voltage is going to be at the collector pin?
(I was under the impression that when the transistor is "on", it has
no internal resistance...)

No, it is NOT 'ON' or 'OFF' as in infinite or zero ohms.

A transistor will conduct a CURRENT determined by its input drive (in this
case the LED current).

This is fundamental basics and you clearly need to read up about how
transistors operate and how to use them.

Graham


.

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