Author Topic: LED Flasher Circuit  (Read 590 times)

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Offline ksbTopic starter

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LED Flasher Circuit
« on: March 04, 2020, 03:31:10 pm »
Hi,
Can someone guide me how to design LED Flasher using BD139 which all the LEDs (max 8 LEDs) must connected in series? What i have found in the net is the LEDs connected in parallel. See attachment.
 

Online Zero999

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Re: LED Flasher Circuit
« Reply #1 on: March 04, 2020, 03:44:34 pm »
The circuit requires a high enough voltage for the BJT to undergo avalanche breakdown and start conducting. The LEDs all drop between 1.6V and 3V and with them all connected in series the voltage is too low for that to ever happen.

See the thread linked below for more information about how the circuit works.
https://www.eevblog.com/forum/beginners/why-does-this-led-blink/
 

Offline rvalente

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Re: LED Flasher Circuit
« Reply #2 on: March 04, 2020, 06:21:44 pm »
Do you really need to use just one transistor? Make it two, much more reliable.

This flasher is more of a prank than a circuit itself
 


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