# Latch Circuit: Beginner

I am trying to implement a simple latching circuit that will turn an LED on if the signal from an AND gate is high (LED latches ON if high, and only way to reset is to remove power). I was thinking of using an SR latch, where I reset to the initial state (resulting in an off LED) then when the signal comes in, I switch the state. However, I don't know if 1) this is the right way to do this (seems a bit too complicated, since I don't need 2 outputs or 2 inputs) or 2) how exactly this would even be implemented in a circuit (especially the initial reset, or the power removal feature).

I hope my question is clear, since I am a beginner and am not sure if my descriptions are technically informative. I appreciate any help!

EDIT1: Attempt 1 Using SCR and Transistor:

• Do you require it to be digital logic? You can also do this with an SCR or TRIAC. Jan 28, 2021 at 17:13
• Yes, the logic comes from 2 comparator inputs. I pass through an AND gate and if both are high, a timer cirucit is triggered. If these timer reaches a given time, then the circuit should latch Jan 28, 2021 at 17:21
• So it sounds like it is the output of the timers that you need to latch, not the input to the timers? Jan 28, 2021 at 17:51
• Yes, that;s correct Jan 28, 2021 at 18:32

You don't need to complicate it with digital logic, just use an SCR.

When power is first applied no current flows through the LED.
After the button has been pressed, then the SCR is latched on and the LED is lit.
The only way to turn it off is to stop current from flowing through the SCR ie. remove power.

simulate this circuit – Schematic created using CircuitLab

EDIT with AND gate control

simulate this circuit

• The AND gate uses 2 comparator input, so if both the comparator inputs are high, then the LED turns on. So I think I would have to replace the switch with something. Jan 28, 2021 at 17:20
• Should I use a transistor here? Jan 28, 2021 at 17:26
• @EENoob see the update with an AND gate to control it. Jan 28, 2021 at 17:49
• So if I understand correctly, if the voltage from AND1 is high, then SCR1 latches ON? Jan 28, 2021 at 18:32
• You might find purchasing a small SCR isn't as easy as you think. Here a link on how to make your own. Can a thyristor be built from two transistors? electronics.stackexchange.com/questions/344321/… Jan 28, 2021 at 19:48