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So this is the Optocoupler I will be using:

https://html.alldatasheet.com/html-pdf/505064/FAIRCHILD/FOD3182/978/2/FOD3182.html

My question is with the schematic of the data-sheet. Using Ni-multisim I can't find any components that have a similar internal schematic, and it looks like most are just some sort of photo-diode connected to a transistor, but their internal schematics are significantly different.

I have another post called "Driving Power MOSFET with Optocoupler Problems (Component FOD3182)".

I guess with this post I'd like to ask if anyone can clarify or expand on what kind of optocoupler this is? And I'm wondering what Rail-to-Rail means and if I am just underpowering this device on the isolation side?

The purpose of this circuit is to make sure the PWM signal is passing through the Opto. I don't have access to test equipment so the way I am doing this is by modulating the intensity of the LEDs.

The program I'm running will incrementally increase and decrease the duty cycle of the PWM signal to make the LEDs on both sides of the coupler increase and decrease intensity at the same ratios, allowing me to visually check that it is working correctly.

I do have a basic multi-meter but the coupler does not seem to be blocking the voltage from the supply at all, and is not modulating the intensity of the isolation side LED.

I know it's not a defective product as I have 12 and this is happening with each one I use.

Once I get this working I'm wanting to use it this to drive some power Mosfets instead of the LED, so I can drive a sensored BLDC motor.

I'm also a bit new to this site, so any pointers or tips of any sort regarding my problem or Stack Exchange in general are welcome.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Why is the voltage source on the output side labelled "PWM"? If it is PWM-controlled, what source is controlling it? \$\endgroup\$
    – The Photon
    Commented Jan 21, 2021 at 20:12
  • \$\begingroup\$ Also, are you sure you didn't blow up the load LED? Applying 12 V to an LED is likely to do that. \$\endgroup\$
    – The Photon
    Commented Jan 21, 2021 at 20:13
  • \$\begingroup\$ @ThePhoton So the PWL on the voltage source is a something generic from the schematic program on stack. Its just a 12V motorcycle battery, and no the LED isnt blown out as the 1k resistor is dropping the amps to 12mA and the LEDs Im using are rated to 16V \$\endgroup\$
    – The_N
    Commented Jan 21, 2021 at 20:50

2 Answers 2

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That is an isolator with a high current (3A!) push-pull output stage. It can't be supplied with power through an 1k resistor. Move the resistor in series with the LED.

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  • \$\begingroup\$ Gratzi, so the +12V should be directly connected to VDD and VSS grounded? Much appreciated senior I'll be testing this solution tonight. I cant upvote but muchos gracias \$\endgroup\$
    – The_N
    Commented Jan 21, 2021 at 21:08
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You connected the Anode and Cathode backwards.

FOD3182 OptoIsolator Block Diagram

The FOD3182 expects the positive voltage at the Anode, from which it powers its internal LED.

https://www.onsemi.com/pdf/datasheet/fod3182-d.pdf

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