Is there a way to keep an LED turned on even when the power source is off?

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SUMMARY

The discussion centers on creating a circuit that allows an LED to remain illuminated even when the power source, specifically a Raspberry Pi, is turned off. The user seeks a device that functions oppositely to a standard NPN transistor, allowing current to flow from Collector to Emitter when the Base is at 0V. A PNP transistor circuit is recommended as a solution, enabling the LED to stay on when the GPIO pin is low and turn off when the GPIO pin is high. This approach ensures a solid-state solution suitable for environments with significant vibration.

PREREQUISITES
  • Understanding of PNP transistor operation
  • Basic knowledge of GPIO pin functionality on Raspberry Pi
  • Familiarity with LED circuit design
  • Awareness of solid-state components and their applications
NEXT STEPS
  • Research PNP transistor circuit configurations for LED control
  • Explore GPIO pin programming on Raspberry Pi for controlling output states
  • Investigate solid-state relay alternatives for high-vibration environments
  • Learn about current limiting resistors in LED circuits to prevent damage
USEFUL FOR

Electronics enthusiasts, Raspberry Pi developers, and engineers designing circuits for environments with high vibration, particularly those needing reliable LED control.

andrew700andrew
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Hi, I'm looking for a device like a transistor which preforms the opposite. E.g.

On an NPN when Base is +0.7V current can flow through the Collector to the Emitter and when the voltage at B is 0V (i.e. a switch connected to base is open) no current will flow from C to E. I want the opposite of this to happen. So when the Base voltage is 0V (i.e. a switch connected to Base is open) current CAN flow from Collector to the Emitter and when the Base voltage is +0.7V no current can flow from C to E.

Does a device like this exist, or can I do something to make it work? For some context, this will be on a circuit with the GPIO pin of a raspberry Pi connected to Base with an LED connected to the Emitter. I want it so that even if the raspberry Pi turns off (and the GPIO pin turns off), the LED will remain ON, only when the GPIO pin of the Raspberry Pi is high will the LED be turned off.

Also, I will need the system to be solid state as it will be exposed to serious vibration so any mechanical parts like a mechanical relay switch (which would work I assume) will likely fail.

Thanks.
 
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PNP transistor circuit will likely do the trick
 
Try this circuit:
upload_2015-2-6_17-24-59.png
 

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