Can Solid State Relay Be Used For Data? - Page 1
Forum section: electronics / projects

author: pacmann
author_rank: Contributor
timestamp: October 30, 2023, 08:04:15 am
content: Can DC/AC MOSFET solid state relays like TLP172 be used for sending 3.3V digital data (10MHZ) through drain 1 and drain 2?Cheers

author: wraper
author_rank: Unknown
timestamp: October 30, 2023, 08:20:02 am
content: Sending signal through yes, turning off can be a problem due to 20pF typical output capacitance. But you should not do this anyway even if it worked.

author: Psi
author_rank: Super Contributor
timestamp: October 30, 2023, 08:21:37 am
content: Sending data yes, sending data at 10mhz probably not.

author: pacmann
author_rank: Contributor
timestamp: October 30, 2023, 09:16:04 am
content: Quote from: wraper on October 30, 2023, 08:20:02 amCan you kindly explain why its not a good idea to use for this?

author: Psi
author_rank: Super Contributor
timestamp: October 30, 2023, 09:40:05 am
content: Because your output signal will look like crap at 10mhz, due to the 20pF of capacitance.To output the signal the detector capacitance has to be charged up, which takes time from the energy hitting it from the solar array inside.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 30, 2023, 09:53:08 am
content: Quote from: pacmann on October 30, 2023, 08:04:15 amAs above, suresendingdata is fine.The problems arise when you want to turn off the data.You need to ensure the isolation to the 10MHz is enough to defeat false RX, and the 30pF is ballpark 530 ohms at 10Mhz so you'd need maybe 50 ohms loads.If you pick a MOS device with lower capacitance, you might be able to do something.

author: wraper
author_rank: Unknown
timestamp: October 30, 2023, 10:02:52 am
content: Quote from: Psi on October 30, 2023, 09:40:05 amHe asks about using it as relay to switch the signal, not pass it through the LED. The problem is with turning it off. Using it for signal isolation will not work at all even if signal is 1000 times slower.Quote from: pacmann on October 30, 2023, 09:16:04 amBecause it's a wrong part for the task. For digital signal use for example AND gate controlled by a regular transistor output optocoupler. Or switch IC like 74CBT1G125 if you want exactly switch and not logic gates.

author: Nusa
author_rank: Super Contributor
timestamp: October 30, 2023, 10:10:45 am
content: Quote from: pacmann on October 30, 2023, 08:04:15 amFor the TLP172, no, unless you're willing to live with Hz, not MHz. Just look at the datasheet switching characteristics. For the TLP172G turn-on time 0.5-1 ms. Turn-off time 0.1-0.5 ms. It's meant to switch power, not data.That said, search for "high speed optocouplers" that are designed for network interfacing.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 30, 2023, 07:20:33 pm
content: Quote from: pacmann on October 30, 2023, 09:16:04 amFind some better data, and it shows the trade offs.https://api.pim.na.industrial.panasonic.com/file_stream/main/fileversion/179643This part has two choices, low R or low C.https://datasheet.lcsc.com/lcsc/1912111437_PANASONIC-AQY221N2S_C425153.pdfIf you want to use the MOSFET output as a series gate/relay, you need a low Cout version, commonly spec'd for RF.

author: pacmann
author_rank: Contributor
timestamp: October 31, 2023, 02:05:06 am
content: Thanks all. I want to switch data on a pin that accepts analog and digital inputs.I want to connect the pin to my micro controller gpio when in "digital" mode only and block the analog otherwise. The analog can get up to +10 to -10v and it will damage the micro. I thought ssr will act like mechanical relay to solve this problem but now I know it has higher capacitance. Is there a good way to do this?

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 31, 2023, 06:37:07 am
content: Quote from: pacmann on October 31, 2023, 02:05:06 amIt sounds like you do not need isolation, and any decision to switch any relay, would be delayed so pin damage could already occur.Common would be to use a series resistor with clamp diodes, to manage the Analog over swings, and then you add a small capacitor in parallel with the resistor, so the high speed digital edges 0-Vcc still make it through.If you want to measure the full -10 to +10 swing, at the micro so reduced to a 0-3.3Vcc span, things get trickier, as your Analog gain could be 1/6, so you need to remove the divider elements when you have a digital data drive, when you want 1:1.A CMOS analog switch (x2) could manage that.