Custom sub-circuit model: VTL5C6 analog opto-isolator


Senior Member
While I was working on the virtual circuit of a frequency controlled delay, I was looking up 'proper' voltage (or current) controlled resistors, and most of the results talk about the use of the Jfet, which I found to not be bidirectional. Next, I found an analog optocoupler on Rapidonline, which suits my application well. However, there's no model of it on picaxe VSM.

I've created a sub-circuit which uses an arbitary ccvs linked to a voltage controlled resistor to mimics this analog opto-isolator / opto-coupler.

I was creating a formula in the excel spreadsheet with a logarithmic graph to help me match it with the VTL5C6 current vs resistance graph in this datasheet on rapidonline. Then, I copied this formula into the arbitary model's formula field, and validated it so it is ((100/(((I(A,B)*1000)^1.4)+0.001))+2.2)/10000. The extra /10000mV is added so the voltages are more in range with the simulator. After this, I thoroughly tested it with the test circuit.
The settings for the voltage controlled resistor in the sub (does the Min and Max parts):
- On voltage: 10
- On resistance: 100M
- Off voltage: 0.000275
- Off resistance: 2.75k

Here, I've attached a compound diagram to show users what it looks like, before downloading the .dsn file which comprises of the VTL5C6 sub-circuit, and a test circuit around it (including my resistance meter subcircuit)
The LED is in the subcircuit to sustain the LED effects on the input (forward voltage drop...).

I have not included the time delay to reach 100M ohms @ 0mA yet.

The formula which creates the graph is =((100/((B1^1.4)+0.001))+2.2).


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