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LED flasher does not work need help.

audioguru

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Most Helpful Member
Try a 100k resistor.
Then with the 3V supply, the base current is only 2.3V/100k= 23uA and it saturates well only when its collector current (LED current) is only 0.23mA.
That is why I said the original 47k resistor (used with a 9V supply) has its value too high.
 

gary350

Well-Known Member
Thread starter #163
Then with the 3V supply, the base current is only 2.3V/100k= 23uA and it saturates well only when its collector current (LED current) is only 0.23mA.
That is why I said the original 47k resistor (used with a 9V supply) has its value too high.
The circuit I found online was 9v but it runs good on 3v.
 
Last edited:

audioguru

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Most Helpful Member
The circuit I found online was 9v.
Then with only 3V the base current with the 47k resistor is only (3V - 0.7V)/47k= 48.9uA but the transistors saturate well when their collector currents are 489uA which results in a very dim LED especially if the hFE of the transistors are a little low and the 3V battery voltage has dropped a little to 2.7V.
 

audioguru

Well-Known Member
Most Helpful Member
Could it be that your simulated transistors are exactly alike? How could the circuit be astable if all the components are the same?
All the parts are rarely all the same. The transistors have a wide range of hFE, the resistors and capacitors have plus and minus tolerances that are never the same.
Besides, even in all the parts are exactly the same then a little noise from the transistors and resistors will set off the oscillations.
 

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