I have many test points on a board, a small DAQ, and an SMU that I can program with LabView. Depending on the test, I need to change which test point the SMU is sending/measuring voltage or current.

To do this, I figured I should use a series of analog switches, and control the switch paths by using the DAQ's few outputs. (Eg. Outputting the high/low binary 000 sends the signal to the first test point TP1; 001 routes the SMU to TP2, etc.)

However, some of the tests I'm automating require sourcing/sinking up to 500mA of current from the SMU to the test point, and most switches advertise their "high-current capacity" of 150mA or so. Additionally, my SMU signal reaches a maximum of 20V at times, so it needs to be able to handle both.

I find it hard to believe that there isn't a switch that can do what I need, so what should I be searching for?

Is this usually how this kind of task is accomplished, or is there an alternative to switches that would be better?

  • \$\begingroup\$ Welcome. If the test points are isolated, could they have independent loads? Or does each input have optional loads? Please clarify. \$\endgroup\$ – Sparky256 Jul 10 at 21:20
  • \$\begingroup\$ Sorry, I'm not sure what you mean by "optional loads". The board that I'm testing has a bunch of circuit paths between the test points and GND, so I'm typically taking measurements of voltage or impedance from TP## to GND, while optionally (depending on the test) sinking/sourcing current to the same (or different) test point to GND. But I believe they are all part of the same circuit. I'm not super experienced so if my response doesn't answer your question, could you elaborate what you mean? \$\endgroup\$ – Alex G Jul 10 at 21:57

While you could look for analog mux's and switches, not many go into that range. Why not use relays? Relays support both wide voltage ranges and high currents.

Analog mux's have a varying resistance which may not sit well for your testing.

Relays have what is to be considered constant resistance and it's low usually under 1ohm.

Search for relays or SSR's at your favorite distributor.

  • \$\begingroup\$ Awesome, thank you! Do you mind elaborating why someone would use an analog switch instead of a relay? I keep seeing "Automated Test" under the "Applications" section for the datasheets, and I can't figure out why. Eg. Some of them have huge "on" resistances, which would affect the measurement readings (and if they're much greater than the circuit you're measuring, might (I think) make a measurement inaccurate). \$\endgroup\$ – Alex G Jul 10 at 22:09
  • \$\begingroup\$ Relays are power intensive and bulky, for most test fixtures neither of those things matter normally. Relays are also easier to make prototypes with. Relays also cost more. \$\endgroup\$ – Voltage Spike Jul 10 at 22:22

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