The ohmmeter shows wrong output resistance of an optocoupler in Proteus

Thread Starter

Generation

Joined Apr 4, 2020
11
In the attached Proteus circuit I used optocouplers NSL-32SR3. Its dependence on the LED current is depicted in the attached graph.
Unfortunately for some reason the ohhmeters show always 100MOhms, and it doesn't matter on the applied to LED current.
 

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ci139

Joined Jul 11, 2016
1,561
Do you have any series Collector or Emitter Resistance ? Does your Vs/Vcc/Vdd has any internal resistance ? (←at least one of these is required)
 

MisterBill2

Joined Jan 23, 2018
6,324
Do you have any series Collector or Emitter Resistance ? Does your Vs/Vcc/Vdd has any internal resistance ? (←at least one of these is required)
An ohm meter in a simulator will not be an accurate device, as you have discovered. And a photo transistor needs a bias source and your circuit does not have one. Make it a series loop with a 10K ohm resistor and a 10 volt battery and then read the voltage across the photo-transistor. And add a series current meter and you may be able to calculate the resistance.
 

ci139

Joined Jul 11, 2016
1,561
as any transistor the coupler also has the V.collector dependency usually the lower V.c --
-- (the higher the in series collector resistance) the lower the R.CE.ON
 

Thread Starter

Generation

Joined Apr 4, 2020
11
An ohm meter in a simulator will not be an accurate device, as you have discovered. And a photo transistor needs a bias source and your circuit does not have one. Make it a series loop with a 10K ohm resistor and a 10 volt battery and then read the voltage across the photo-transistor. And add a series current meter and you may be able to calculate the resistance.
Is it the same procedure if we use photoresistor instead of phototransistor?
 

Reloadron

Joined Jan 15, 2015
5,508
Is it the same procedure if we use photoresistor instead of phototransistor?
Difference between photoresistor and phototransistor | photoresistor vs phototransistor
Read and learn. The answer to your question is no. Photo transistors have a fast response, even faster than a speeding bullet. Photo transistors also tend more to be On/Off devices and used in applications where their use is practical. You choose a component based on its intended application. Before asking more questions how about answering some which have been asked of you?

Ron
 
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