led arrangement

ash20

New Member

• Jul 18, 2011

• #1

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??

 

Z

Zener_Diode

New Member

• Jul 18, 2011

• #2

Led Arengment

1. see attachment
2. make yourself more clear

 

Attachments

• Leds.jpg

  90.5 KB · Views: 135

Grossel

Well-Known Member

• Jul 18, 2011

• #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.

 

ash20

New Member

• Jul 18, 2011

• #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??

 

C

carbonzit

Active Member

• Jul 18, 2011

• #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.)

 

V

vivid2012

New Member

• Jul 18, 2011

• #6

Zener_Diode said:

1. see attachment
2. make yourself more clear

Click to expand...

nice attachment, well done brah.

 

ash20

New Member

• Jul 19, 2011

• #7

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

 

W

wandek

New Member

• Dec 7, 2012

• #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.

 

JimB

Super Moderator

Most Helpful Member

• Dec 7, 2012

• #9

but i don't understand why they are breaking the rule about led circuit

Click to expand...

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

Click to expand...

Relying on the internal resistance of a small battery to limit the current, most likely.

Nothing magic, just marginal design.

JimB