Opto-isolator 4N35 simulation

I'd like to try different assembly with an opto-isolator 4N35 It contains a LED optically coupled to a photo-transistor.

Here the datasheet : http://pdf1.alldatasheet.com/datasheet-pdf/view/520953/AVAGO/4N35-000E.html

I found LED in the component list but no photo-transistor. Can you help me?

by brisfan
March 06, 2017

2 Answers

Answer by mrobbins

This old circuit of mine simulated an optical connection between an LED and a photodiode (not transistor) -- run the DC Sweep simulation:

I modified it to work with a phototransistor, where the photocurrent now stimulates the base-collector junction. This is not tuned to match your exact part number, but take a look -- run the DC Sweep simulation, as well as the Time Domain simulation if you like:

If you wanted it to match your 4N35 part exactly, you'd have to modify the simulation parameters of D1 to closely match the embedded LED, and modify the simulation parameters of CCCS1 and Q1 to closely match the embedded phototransistor.

+1 vote
by mrobbins
March 06, 2017

Thank you for your answer. I'm a beginner in electronic and I fear to not have skills and experience to do that. But I'm going to try.

by brisfan
March 06, 2017

Answer by brisfan

Hi, I'm trying to set LED characteristics to fit with 4N35 opto-isolator. For the 4N35 I found in the datasheet :

  • foward voltage is 1.3 at 10 mA.
  • capacitance is 25 pF.
  • Rise and fall times 2┬Ás.

In CircuitLab for a LED I had to set :

  • the saturation current => maybe 10 mA ?
  • the ohmic series resistance => ?
  • the zero bias junction capacitance => 2.5e-11 F
  • the junction built-in potential => ?
  • the emmision coefficient => ?
  • The transit time => maybe 2e-3s
  • the junction grading parameter => ?
+1 vote
by brisfan
March 29, 2017

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