Quick question from a newbie. I recently bought several LEDs in the 8000 mcd and a couple of flashers in 1500 mcd.
I have worked out the resistors values I need.

What I need to know is if everyone solders the resistor to the anode (long) side of the LED.

My next question is regarding the flasher LED. Its flash rate is 2.4Hz under 10V which is is forward voltage and its 30mA.
My DC power source will be 4.8 Volts at 1.2 Amps. Should I have a resistor on the LED even though I am running 5V instead of 10V

 

well, you can solder the resistor on any led it won't make a diffrence.

yes you should still put a resistor on the flashers, the power source you are using is 1200ma and you only want 30. i cannot work out the right values though, i just use 1k.

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when you post that reply, im just kidding.

 

Not clear question, I think you should clarify ! ther are mistakes in the construction of your sentense.


I'm ver amazed for exist of such Led of 10v forward voltage! Anyway if that's right you couldn't light that led with 5v power supply ! Another thing, the resistor is to connected in series of led in case you want to protect your led from excess current that might flow thourgh the led branch so the current of your generator 1.2mA is less than that of led maximum current, there's no problem concerning to current!

Anyway you won't loss anything if you open this link as I wrote below this post of mine :wink:

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Tourism in syria website:
http:///www.syriatourism.org

 

sorry , i wrote 1.2mA , I haven't paid attention of that

__________________
Tourism in syria website:
http:///www.syriatourism.org

 

Here are the specs on the flasher LED nominal is 5V max is 10V
http://www.superbrightleds.com/specs/bw1520_specs.htm

Thanks for the info. I will place a resistor on the flasher.

 

The LED doesn't have a forward voltage up to 10V, it's the Cmos blinker circuit in it that operates from 3V to 10V like any ordinary Cmos IC.
I suspect that it doesn't need a current-limiting resistor since the Cmos circuit in it will limit the current. It will be at its max of 30mA with 10V, its nominal of 20mA at 5V and hardly work at 3V.

Somebody said to use a 1k resistor as a current-limiting resistor. Then for 20mA it will need 20V more!

4 Electros,
The site that you mentioned is stupid. They have a chaser project that they say lights one LED at a time, but they use a separate current-limiting resistor for each LED when only a single resistor is fine. Put the single resistor in the common voltage feed to the LEDs to reduce their current from about 12mA without a resistor.

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Uncle $crooge

 

Some flashing LEDs dont need an curent limiting resistor.It just needs to be the right voltage.

But you beter put one in in case its not one of those.

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Il give you shocking experience.

 

You ware a litle faster then me audio.3 minutes to be exsact(check the times.)

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Il give you shocking experience.

 

I would one test for a resistor with an LED with cmos circuit ?

Would a 0 Ohm 1/4W Carbon Film Resistor be good. I actually dont understand a 0 ohm resistor. Like I said I am new to all of this.

The application is on an R/C aircraft and the LEDs will plug directly into the receiver which puts out 4.96 V according to my DVM. I calculated all my LEDs at 5V for the resistors value.

 

someone once told me he burnt his led's when he connected the resistors to the cathode, but they worked fine when connected to the anode. i think this is a case of practical going against theory.

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Everybody can but not everybody will.

 

He proboby messd up somting.

an 0Ohm resistor wod be a pice od wire.

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Il give you shocking experience.

 

You said you have a 4.8VDC power source. If the LED is red then it needs about 2V across it. If the blinker circuit is perfect then to get 20mA through the LED the total resistance in series with the LED must be at least 140 ohms according to Ohms Law. The closest higher standard value for a resistor is 150 ohms so try one in series with the circuit.
If the LED isn't bright enough then reduce the value of the resistor.

The output of the receiver isn't perfect and therefore its voltage will drop when loaded. It might not be able to supply 20mA to anything without having a transistor to boost its current.

That's where you got zero ohms from. If the battery voltage was lower would you use a negative resistance?

You don't have an LED, you have a blinker circuit. Its spec's don't say how much current it draws with a 4.8V supply. Maybe it is perfect and limits the current to exactly 20mA with any supply from 3V to 10V.
You don't know how much current can be driven by the output of your receiver but you can find out by trying it.

Now you say it is for an RC aircraft and you are using more than one flashing LED. The battery will be drained in nearly no time.
If I was you then I would make a blinker circuit that blinks the LEDs for very short bright pulses, therefore the battery will last for a long time like in my Ultra-bright LED Chaser projects:
http://www.electronics-lab.com/proje...004/index.html
http://www.electronics-lab.com/proje...003/index.html

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Uncle $crooge