Led to stay on after power is turned off

15/07/2025

Posted by:
codepuncher

I am try to build a 9v circuit, when power is supplied it turns on an Led.
Even when the power supply is turned off the Led must stay on until a reset button turns it off.

I have tried using 2N2222 transistor but can`t figure it out.
Thanks for any help

15/07/2025

Posted by:
andrew

Hi

What you need is a SR latch circuit. This web page shows how you can make an SR latch using transistors.

You will need to adjust the LED resistor value to use it at 9V.

CodeSys

Multi-function IO Expansion Card for Raspberry Pi-3

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