Solid State Relay Circuit Symbol?

Shadrack

What is the symbol for a solid state relay? I've been using mechanical relay representations in my documentation and just writting next to it "solid state."

I don't like doing this, because it implies that the relay is an inductive load, which it isn't...

My thought is that it should look like or similar to an opto-isolator, with a current path through an LED that's output effects the base of an NPN transistor. Most of the relays we used are isolated anyway, so they probably work this way.

What are your thoughts?

Thanks!
-Shad

berkeman

Maybe use a FET switch symbol... Do you know how the solid state switch is constructed?

dlgoff

The load side is usually shown as back to back diodes. I think the input is just a couple of terminals located next to the diodes.

Regards

berkeman

I googled solid state relay schematic symbol, and got lots of hits (not all useful). Here's a link to a datasheet for a highside SSR from STMicroelectronics. The block diagram in Figure 2 would be a good starting point for drawing a schematic symbol. I'd probably simplify it to the output MOSFET and input hysteresis gate, or something similar. I like to draw enough info in schematic symbols like this to remind me of some of the limitations and features of a particular device. For example, what's the difference between a high-side and low-side SSR? Why are they different? What would you have to have to make a more bi-directional SSR?

http://www.st.com/stonline/products/...re/ds/1079.htm

dlgoff

capnahab

The way I have seen this component represented is by a small square box with SSR (solid state relay) written in it. Then the numbers 1-4 in each corner for the terminals.