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Electronic newbie here.

I'm trying to use a TLP222A as a remote switch for a small signal (3V and about 150-200mA at most).

It's super simple, but I can't understand why the following happens:

I'm powering the TLP222A connecting pin 1 and pin 2 (anode and catode) directly to a power supply that provides 5V and 40mA, connecting and disconnecting the anode with a momentary switch.

First, I have tried to turn on and off a led connecting it to the same 5V and ground through the TLP222A and it works perfectly. The led turns on when I connect pin 2(anode) to 5V and it turns off when I disconnect it.

schematic

simulate this circuit – Schematic created using CircuitLab

(D1, D2, D3, M1 and M2 are part of the TLP222A)

Then, I have tried to connect two cables to pin 3 and pin 4 to check if I have conductivity when pin 1 and 2 are connected to the power supply. The tester never indicates conductivity.

I have also tried to connect the cables to the device that I want to control remotely and nothing happens.

schematic

simulate this circuit

Could someone help me to understand what is wrong in my approach?

Thanks

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  • \$\begingroup\$ What the heck is a TLP222A? Can you provide a link to the manufacturer's datasheet? Also, please use the built-in schematic editor to draw a schematic of your circuit. \$\endgroup\$ – Elliot Alderson Nov 2 '19 at 20:49
  • \$\begingroup\$ Sorry, I didn't know that I stack exchange has a built-in schematic editor. I've added the schematic for both cases. \$\endgroup\$ – Garet Nov 3 '19 at 23:20
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Continuity Tests should not be performed on a powered circuit. You will, most likely, get misleading results and, at worst, end up with a busted continuity meter.

Also, you probably already realize this but the power and ground associated with pins 1 and 2, should be physically isolated from the power and ground associated with pins 3 and 4, or you're not getting much utility out of an optical-isolator.

enter image description here

Note you need a current limiting resistor, to limit the current in the path through pins 1 and 2 (which are the internal LED) to about 50mA, as per the test circuit in the datasheet (and the absolute maximum ratings table):

enter image description here

I'm pretty sure pins 3 and 4 are symmetric, but one of them should be connected to your load-side ground.

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You really shouldn't be connecting the LED of the TLP222A directly across a 5 V power supply. It's only rated for 50 mA continuous, and it only worked the first time because the power supply went into current limiting. Always use a series resistor.

I suspect that you've blown the diode, which is why it has stopped working.

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  • \$\begingroup\$ I'm powering the TLP222A with 5V and 40mA, so it's under the limit. I have been able to reproduce the same test without problems multiple times.. I don't think the diode is blown yet \$\endgroup\$ – Garet Nov 4 '19 at 20:11

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