I have to design a circuit where a momentary switch is used to control the main power of board. Since its a momentary switch I have a requirement of latching relay. Using only one switch I have control turn On and turn Off of the board. Once press the switch and release switch, power is On and it remains in the ON state as long as switch is is pressed once again. I press it again the power should turn OFF. Hence I understood that I should use latching relay in my design. I have selected 1937650-9 from TE. Can someone please explain me the working of this. If i consider this relay my design will look something like attached image. Im still not sure whether this relay would fulfill my requirement. How would the relay get to know that in first press of switch, the set coil has to energize and output should be latched. And when I press the same switch for second time, the reset coil will energize. Can someone please explain me how the selected relay works. Or the relay that I have selected is not a correct one for my requirement. If its not a suitable one for my requirement can someone suggest a alternate relay..enter image description here

  • \$\begingroup\$ As a suggestion, when I am unsure of how a IC/component works, I buy one of each (of the components I think will do the job) and hands-on testing them to find out (with the help of datasheet). I don't know how this one works, so I would do the same. Buy one and start playing with it \$\endgroup\$ Commented Jun 4, 2021 at 18:57
  • \$\begingroup\$ Seeing as you have wired up A3, you must have bought the 2 coil version. However as you have got it wired there, when you press the button the 2 coils will both be powered and will fight against each other. \$\endgroup\$
    – HandyHowie
    Commented Jun 4, 2021 at 19:07
  • \$\begingroup\$ There is a CircuitLab schematic drawing button on the editor toolbar. Double-click a component to edit its properties. 'R' = rotate, 'H' = horizontal flip. 'V' = vertical flip. Note that when you use the CircuitLab button on the editor toolbar and "Save and Insert" on the editor an editable schematic is saved in your post. That makes it easy for us to copy and edit in our answers. You don't need a CircuitLab account, no screengrabs, no image uploads, no background grid. \$\endgroup\$
    – Transistor
    Commented Jun 4, 2021 at 19:16
  • \$\begingroup\$ Why do you want to use a relay when you can use a toggle flip flop and FET switch to bridge the DC voltage whenever AC is available or disable your SMPS and define the power on reset condition at will with memory or by capacitor voltage at reset with bias R . You can even do the same with a standby voltage to power the logic and drive an electromechanical SPST switch \$\endgroup\$ Commented Jun 4, 2021 at 20:09

1 Answer 1


The datasheet shows that the 1937650-9 is a 24 V, bistable 2-coil relay.

enter image description here

Table 1. The datasheet shows that the 2-coil relay has a common + terminal (A3) and that to operate the relay you connect A2 to '-' and to reset it you connect A1 to '-'.


simulate this circuit – Schematic created using CircuitLab

Figure 1. How the bistable 2-coil relay is intended to be operated.

You can't do what you want with one relay and a push-button unless you use the impulse relay I showed you in your previous question, How to select a relay for main power input.

stepping relay

Figure 2. The pawl mechanism is advanced on every impulse of the relay coil. Image source: HomoFaciens.

  • \$\begingroup\$ Do you have any impulse relay in your mind. If you could suggest a part number it would be helpful \$\endgroup\$ Commented Jun 4, 2021 at 19:39
  • \$\begingroup\$ No. I've never used one. Also, be aware that on power down these relays don't reset and will power up in the same state that they switched off. \$\endgroup\$
    – Transistor
    Commented Jun 4, 2021 at 20:33

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