Flashing LEDs - resistor or not resistor? - Electronic Circuits Projects Diagrams Free

grrr_arrghh · 17th March 2003, 07:11 PM

Hi. A friend told me that you don't need a resistor in series with a flashing LED. Is this true? if so, why?

Thanks

Chippie · 17th March 2003, 07:13 PM

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

What voltage flashing led ?

what supply volts are being used ?

grrr_arrghh · 17th March 2003, 07:17 PM

ermmm, i don't really know. the sort you would use with a 9V battery...

bogdanfirst · 17th March 2003, 07:44 PM

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?

Gene · 17th March 2003, 10:27 PM

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.

Pilot · 17th March 2003, 11:29 PM

Have a look at kingbright.

eg. http://www.kingbright-led.com/data/spec/L56BID.pdf

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.

bogdanfirst · 18th March 2003, 07:00 AM

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?

**kinjalgp** · 18th March 2003, 09:55 AM

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.

grrr_arrghh · 18th March 2003, 09:24 PM

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!!

bogdanfirst · 18th March 2003, 09:35 PM

when dont you use it?
there are little circs that dont require it.....maybe some flashers.

**mechie** · 19th March 2003, 10:27 AM

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.

grrr_arrghh · 19th March 2003, 08:23 PM

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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17th March 2003, 07:11 PM	(permalink)
grrr_arrghh	Flashing LEDs - resistor or not resistor? Hi. A friend told me that you don't need a resistor in series with a flashing LED. Is this true? if so, why? Thanks

17th March 2003, 07:13 PM	(permalink)
Chippie	There is insufficient information to make a reasonable judgement.......... What voltage flashing led ? what supply volts are being used ?

17th March 2003, 07:17 PM	(permalink)
grrr_arrghh	ermmm, i don't really know. the sort you would use with a 9V battery...

17th March 2003, 07:44 PM	(permalink)
bogdanfirst	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?

17th March 2003, 10:27 PM	(permalink)
Gene	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.

17th March 2003, 11:29 PM	(permalink)
Pilot	Have a look at kingbright. eg. http://www.kingbright-led.com/data/spec/L56BID.pdf 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.

18th March 2003, 07:00 AM	(permalink)
bogdanfirst	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?

18th March 2003, 09:55 AM	(permalink)
kinjalgp	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. __________________ "There is no way to peace, peace is the way!"

18th March 2003, 09:24 PM	(permalink)
grrr_arrghh	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!!

18th March 2003, 09:35 PM	(permalink)
bogdanfirst	when dont you use it? there are little circs that dont require it.....maybe some flashers.

19th March 2003, 10:27 AM	(permalink)
mechie	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. __________________ I need a memory upgrade ... My head is full !

19th March 2003, 08:23 PM	(permalink)
grrr_arrghh	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