# Electronic Circuits and Projects Forum

1. ## led arrangement

hii all,

well i would like to ask the knowledgeable persons that:

1. what is the difference between common anode led arrangement and common cathode led arrangement?? and please explain it with a simple circuit diagram (tht contains just the pwr supply, the led's, may be resistor and ground, and not more if cud be avoided) for both the arrangement.....

2. what is the basic harm in connecting led's in parallel??

2. ## Led Arengment

1. see attachment
2. make yourself more clear

3. I think I know what q #2 is about.

If connecting LED's in parallell whitout one resistor for each led, one led will conduct more, and therefore also have reduced lifespan.

4. @zener diode: can we connect the switch and resistor towards left of led in case of common anode?? isnt it like if we connect them towards right, and there is a high current, the led might blow up coz resistor is put after it ??

@grossel: and what if all led's are of same make?? then can we connect them in parallel??

5. Even LEDs of the same make--even diodes of the exact same model from the same batch--may have different current levels. The ones that draw more current can harm the other ones in a parallel arrangement. (This is counter-intuitive, as we're used to elements in parallel circuits simply drawing whatever they will without affecting adjacent elements.)

6. Originally Posted by Zener_Diode
1. see attachment
2. make yourself more clear
nice attachment, well done brah.

7. okk... thanks to zener diode, grossel and carbonzit.. its clear to me now..

8. but, chinese led emergency lamp use led in parallel and do not use resistor (even just one resistor!). i know they make it because they sell it's cheap. but i don't understand why they are breaking the rule about led circuit. or maybe they have "something" so they can use led in paralel, or they have some technology to handle it in paralel. i want hear fro they to explained about led in paralel. maybe they have some trick i thing.

9. but i don't understand why they are breaking the rule about led circuit
Because the lamp is made as cheaply as possible, with no regard to good engineering to give a long service life.

maybe they have some trick i thing
Relying on the internal resistance of a small battery to limit the current, most likely.

Nothing magic, just marginal design.

JimB

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