Latching a logic signal

Thread Starter

Dritech

Joined Sep 21, 2011
863
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.
 

MaxHeadRoom

Joined Jul 18, 2013
20,717
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.
Max.
 

ErnieM

Joined Apr 24, 2011
8,043
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.
 

crutschow

Joined Mar 14, 2008
24,988
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
 

profbuxton

Joined Feb 21, 2014
419
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.
 
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