0
\$\begingroup\$

In a project, I need to swap the polarity of a 12V power/signal and GND wire combination electronically. The current flow is between 7 and 28 mA.

I'm using a DPDT relay for this - the input wires are connected to the Common terminals, NC and NO are crossed between both relay halves and then go +12V on the board (A) and GND (B). If the relay is unpowered, 12V is connected to the first input and GND to the second one. If it is powered, 12V is connected to the second input and GND to the first.

As the relay (FRT-5) draws quite a lot of current, I would like to substitute it for an analog CMOS switch like the ADG1434 / ADG5434.

Do CMOS switches work on "reverse" current as well, with just a +12V single supply? DPDT relay setup

\$\endgroup\$

1 Answer 1

Reset to default
1
\$\begingroup\$

Do CMOS switches work on "reverse" current as well, with just a +12V single supply?

Actually there is no "reverse" current. The relay connects an output to either GND or +12V. That makes the current flow in one or the other direction.

The same will be true if you use such a switching IC to do the same. So the switches need to be "bidirectional" which they are! So I think these ICs are suitable for what you want.

Do note that when using the ADG5434 each switch has a series resistance of up to 13 ohms so at 28 mA a voltage of up to 0.36 V will be dropper per switch so at the output you will not get +/- 12 V but +/- 11.3 V. The voltage drop will be lower for the ADG1434.

\$\endgroup\$
2
  • \$\begingroup\$ "Bidirectional" is what I'm looking for then, no idea why I didn't think of calling it that. Shouldn't that appear somewhere in the data sheet though? I found some analog switches that market themselves as "bidirectional" (mostly from TI) - are all of Analog's analog switches bidirectional unless specified otherwise? \$\endgroup\$
    – towe
    Apr 9, 2019 at 7:08
  • 1
    \$\begingroup\$ @TobiasWeiß AnalogDevices just talks about these switches as being "real" switches having a certain resistance. A switch can be assumed to work in both directions so I think they didn't feel the need to add "bidirectional". I expect that inside the chip both AD's and TI's are "transmission gates", a very simple and standard circuit which can be made in CMOS technology: en.wikipedia.org/wiki/Transmission_gate \$\endgroup\$
    – Bimpelrekkie
    Apr 9, 2019 at 7:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.