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I have an application which would involve having data lines connected to a microcontroller which would signal at lvttl (3.3v) levels and also take in 24v for a resistive load (~600mA). I have previously used a mechanical relay for this same application without any major issues. I'm in the process of switching the microcontroller on this to something more modern, more powerful, cost effective and much smaller in size and decided to switch out the mechanical relay with a Solid State Relay. This would provide much higher life for the product, help me with making the part smaller and at the same time make manufacturing easier as the pick and place can mount the SMD SSR not requiring me to hand solder these separately.

enter image description here

From the datasheet I'm using connection "C" as that would be more suitable for the load I'm planning.

My issue is: The application my board connects to has a common ground. The lvttl lines and the 24v input both share the same ground, how would I handle that if I'm using a G3VM-61E1 or something similar? It seems internally the logic is similar to an N-Channel style mosfet.

enter image description here So how would I handle giving both my digital signals and HV supply a common ground in this case?

If this isn't the right place to ask this question, please feel free to point me in the right direction or any resource you think is more appropriate.

Thanks,

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  • \$\begingroup\$ Please provide a hyper link to the G3 part. \$\endgroup\$ – Andy aka Jun 17 '20 at 8:11
  • \$\begingroup\$ By connecting grounds you are not benefiting from the galvanic isolation provided by the internal optocoupler of the static relay. More information is needed on the bloc called Application to understand why the ground are connected. Maybe in this bloc the digital outputs at 3.3v and the internal supply of the 3.3 are not isolated from the 24V and I think this is the problem because there is no GND pin for digital signals in the Application bloc. \$\endgroup\$ – Paul Ghobril Jun 17 '20 at 8:17
  • \$\begingroup\$ One thing of note: switching from a relay to a SSR with optocouplers isn't necessarily going to give you longer life. Both relays and optocouplers break over time, with roughly the same amount of operations. If you need galvanic isolation (which in itself isn't obvious), then maybe consider "digital isolators" instead - they internally work with transformers instead of optics. You could combine them with a MOSFET-based driver IC and then you have your own SSR. \$\endgroup\$ – Lundin Jun 17 '20 at 8:35
  • \$\begingroup\$ @Andyaka Here is the link to the datasheet: omronfs.omron.com/en_US/ecb/products/pdf/en-g3vm_61b1_e1.pdf Thanks for the question, any ideas? \$\endgroup\$ – Devesh Rai Jun 17 '20 at 10:52
  • \$\begingroup\$ @PaulGhobril the "Application" is a ceramic heater driver board that accepts 3.3v logic to set and read temperatures of an SPI-Like (not spi because its 15 bit) interface. It has exactly 5 pins exposed via a flat/flexible pcb connector, those are D1, D2, Clk, 24v and Gnd as described in the schematic. Thanks for the question, any ideas? \$\endgroup\$ – Devesh Rai Jun 17 '20 at 10:53
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Answering my own question after testing on a breadboard:

Joining the two grounds together works just fine. There don't appear to be any issues.

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