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X****Liu
How to Make LED Flasher Circuit?
1357 1 Mar 13.2020, 02:10:00

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.

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A****min

Mar 18.2020, 14:34:38

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.

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