Latching a logic signal

Thread Starter


Joined Sep 21, 2011
Hi all,

I am using a current sensor to switch off a relay when a particular motor exceeds its current limit. I want the relay to remain off until a reset button is pressed. What type of latching IC or circuit can I use to achieve this please? Ideally it have to be a simple circuit or a single IC.

Thanks in advance.


Joined Jul 18, 2013
If the current sensor is N.C. then place a N.O. contact on the sensing relay in series with its coil, place a reset or arming N.O. P.B. in parallel with the N.O. contact.
The current sensor will have to have returned to its N.C. state to enable a reset.


Joined Apr 24, 2011
The simplest part is the one you already have: the relay itself. Put a normally open relay contact in series with the relay coil. When the current sensor breaks the circuit this contact will keep it off until the reset button is pressed.


Joined Mar 14, 2008
Here's one way to do ErnieM's suggested circuit. The reset switch won't energize the relay unless the current limit switch is closed (indicating no overcurrent).

Reset Latch.gif


Joined Feb 21, 2014
Simple method: Use a magnetically latched relay. These have two coils operating the same contact set. One coil "sets" the relay and the other coil "resets" the relay. Use your Current sensing to "reset" the relay to off and a pushbutton to "set" the relay to on.