Hello. I recently got my hands on a couple SSRs from Toshiba (model
TLP3553A); I have never used these kinds of components, and so I thought I'd have a play around.
At DC, everything seems to work fine. If I apply a voltage through a resistor to pins 1 and 2, the relay allows a current to flow between pins 3 and 4 in either direction.
With an AC signal (a simple 5VPP sine wave from my signal generator), however, things get pretty strange. Regardless of whether there is
anything connected to pins 1 and 2, the waveform gets through from pin 3 to pin 4 without any problem (except that it seems to be capacitively coupled, so any DC offset goes away if there is no current on the LED. This happens even if I just connect the output of the generator directly to pin 3, and my 'scope probe to pin 4, with the grounds from both tied together, and it seems to be independent of frequency.
I'm not sure what's going on—I'm sure I just don't understand how SSRs work, but I'm not quite sure where to look for an answer. Thanks!
—CC
There's some parasitic capacitance across the outputs so unless you have a lower impedance load, you'll see an output signal. Try connecting a 1K resistor from the output to ground and it should behave as you expect.
Indeed, that does the trick—thank you!