Does order matter? + rant

[Atomic_Sheep]

Hi guys, I was just wondering, lets say we have a simple LED circuit with a battery, a resistor and an LED. Does it matter where the resistor is palced i.e. before the LED or after?

If it doesn't which based on what I've seen i think is the case, why is this case? This is the rant part. My understanding of the way the world works is first come first serve. In other words, if you have an LED that has lets say specs of 10mA and it's I dunno how much LED's are... 2 volts? then if we have a 12V 1A battery, then if we place the resistor after the LED, the LED in my mind should get the full brunt of the electron flow/power/whatever? In the split seconds before the LED burns out, the resistor would be getting 10V 980mA current and basically assuming we've calculated the correct size for the resistor, we have prevented a short circuit from happening but have done nothing in the way of preventing blowing the LED. (according to my calculations, the resistor should be around 10.2 ohms and correct me if I'm wrong... I just did 10V/0.98).

 

[ericgibbs]

hi,
Dont think terms of 'power', think current.
The current the LED/resistor series pair conduct will be the same in either order ie: R > LED,,, LED > R.

The colour of the LED determines the voltage drop across the LED.

 

[nsaspook]

Hi guys, I was just wondering, lets say we have a simple LED circuit with a battery, a resistor and an LED. Does it matter where the resistor is palced i.e. before the LED or after?

In general, put the current limiting device (resistor in this case) first on power or signal circuits unless there is a specific requirement not to do so..

 

[3v0]

In general, put the current limiting device (resistor in this case) first on power or signal circuits unless there is a specific requirement not to do so..

Order does not matter for the reason Eric gave.

 

[nsaspook]

Order does not matter for the reason Eric gave.

Electrically it doesn't but for good industrial electronic design standards it does.

 

[3v0]

Electrically it doesn't but for good industrial electronic design standards it does.

Why do design standards disagree with the physics ?

 

[ronv]

I think what NSA is saying is that if you put the resistor first on the power side there is one less place to short out the power supply. Am I right NSA?
A nit but an ok practice.

 

[nsaspook]

Why ? .....

Because things break and techs need to probe signals with tiny clips on boards with lots of components. What's safer, a led with one leg to ground and the other to a 500 ohm resistor or a led to a power buss with a 5 amp fuse when checking for a bad component?

 

[crutschow]

And the LED is always faster than the fuse.

 

[3v0]

Because things break and techs need to probe signals with tiny clips on boards with lots of components. What's safer, a led with one leg to ground and the other to a 500 ohm resistor or a led to a power buss with a 5 amp fuse when checking for a bad component?

Thanks nsaspook. I can see where it can.

 

[MikeMl]

Since the current through the resistor is the same in the resistor and the LED, the voltage drops are permutable, meaning that
Vsuppy = Vres + Vled = Vled + Vres.

(Don't sleep through Algebra)

 

[MrAl]

Hi,

Current is the same though every element of a series circuit.

 

[3v0]

Eric pointed out the info from the last two posts on the first of this thread.

It has morphed a bit since then.