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Flashing LEDs - resistor or not resistor?

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There is insufficient information to make a reasonable judgement..........

What voltage flashing led ?

what supply volts are being used ?
 
well you definetly need a series resistor....
dont think i know circuits where you don't need a current limmiting resistor.....
i am sure you need one. maybe a schematic could do?
 
The only flashing LED I know of (i.e., running without an external circuit) is a 2.2 volt model with a peak of 4 volts. If you connect this to a 9 volt battery without a limiting resistor, it will flash only once.
 
Have a look at kingbright.

eg. **broken link removed**

They manufacture a range of flashing leds from 3mm to 10mm, no series resistor required with a Vf of up to 13V.

Edit: The flasher chip is built into the led.
 
yes, the flasher is in the led, so the limiting resistors and all you need.
and ill say it one more thing...how often don't we use a limiting resistor?
 
If the duty cycle of the flaher is low, you can also do without the limiting resistor. But this is not at all a good idea. You should always use one to ensure long life of LED.
 
OK, thanks everyone.

I am using a current limiting resistor anyway, and to answer your question bogdanfirst, how often don't we use a limiting resistor? - once!!
 
Constant Current ?

Hi Guys..
Just thought I'd chuck my two penneth worth in..
The flashing LEDs I have (the only ones I can get) are happy with 3.5v to 13v. NO RESISTOR.
The internal circuitry contains both the flasher and a current limiter circuit so the resistor is not required up to 13v.
 
mechie, they sound alot like my flashing L.E.Ds

Mine work with or without resistors, but if you connect them straight to a 9v PP3 battery, they 'pulse', rather than flash!

I have changed my circuit completely and am now using a 555 in astable mode, and a small 12v bulb.

Thanks for the help everyone

grrr_arrghh
 
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