In an automotive 12VDC application, I want to use a pair of 2-coil latching DPDT relays such as Panasonic TXS2-L2-12V (https://www.panasonic-electric-works.com/pew/eu/downloads/ds_61022_en_txs.pdf), and connect the Set coils in parallel and the Reset coils in parallel, such as is shown in Figure 16a and 16b of Panasonic's "Relays Caution for Use" note (https://www3.panasonic.biz/ac/e/control/relay/cautions_use/).

In that note, when the coils are connected in parallel, they recommend placing a diode in series with each of the Set and Reset coils as shown in those Figures.

Question #1 is: Should I also place a coil suppression rectifying diode (e.g., 1N4007 or similar) in parallel with each of the Set and Reset coils?

This posting, while not concerning the connection of the Set and Reset coils in parallel, does suggest using a rectifying diode across each of the Set and Reset coils: How to protect bistable latching 2 coil relay with diodes?

Question #2: I plan to activate the Set and Reset coils via a manual SPDT momentary (On) toggle switch. Coils will be 12VDC. I plan to put the switch on the ground side of the coils (between the coil series diodes and ground). The relay data sheets I've read say that subsequent latching pulses after the first pulse on either the Set or Reset coil have no effect, so is it reasonable to expect things to work OK with a non-debounced, manual SPDT switch controlling the coils?

Thanks, Doug

  • \$\begingroup\$ @DRuth it may be good in the future when posting questions to be more specific and include information about the circuit you are trying to design. There is a circuit editor for use when posting questions, it helps to draw a diagram because its easier for readers to understand your design. Its also good to include all information, like the load your driving. \$\endgroup\$ – laptop2d Sep 8 '16 at 20:11

It depends, if your worried about an overvoltage condition on the line, then yes you do need a diode. The relay will open and the magnetic field will cause an overvoltage on the lines connected to the coil. If you have other IC's connected to the power side I would strongly consider a flyback diode. If it's an automotive application a flyback diode would also be warranted because you don't know what else is on the 12V line. If it's a motor or resistive load I wouldn't worry about it too much.

As far as the switch debouncing goes, it depends on your application again. The relay could follow the switch depending on the timing of switch 'bounce'. If the application is a 'dumb' load and it can handle being turned on and off for a 10's of microseconds (potentially) then you don't need to worry about debouncing. If it is a microprocessor or something with digital logic, then debounce the switch. If you have a high current load its probably a good idea to debounce the switch to be nice to the relay's contacts.


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