LED resistor difference on (+) or (-) ?

[Cogtx]

I've been using LED's lately for simple mods and lighting devices and noticed that some people place the limiting resistor on the (+) lead of the LED and others on the (-) lead. Is there a real difference which could effect the LED or power source? Is there a benefit of one over the other and for what type projects/designs? Just curious....thanx

 

[blahblah99]

For your application (and many others), there's absolutely no difference.

 

[CTho9305]

Originally posted by: blahblah99
For your application (and many others), there's absolutely no difference.

Ok, you've got me wondering. When is there any difference at all between the order of components in a series circuit?

 

[DoubleUhat]

Say, if u r doing some diy project, your circuit uses +12VDC and negative ground, i suggest you put the resistor on the anode side so that if the anode leg of the LED touch the mounting chassis (if the chassis is metal and common grounded) only the current limiting resistor is heating up, not a problen at all if the cathode leg touch the chassis, only permenantly light on LED. But if you connect the resistor to the cathode side and let the anode leg (+12VDC) touch the chassis, you may blow away your PSU.

 

[Cogtx]

DoubleUhat...that's a reasonable suggestion which seems to make mucho sense to me...thanx for the input....

 

[syberscott]

Originally posted by: DoubleUhat
Say, if u r doing some diy project, your circuit uses +12VDC and negative ground, i suggest you put the resistor on the anode side so that if the anode leg of the LED touch the mounting chassis (if the chassis is metal and common grounded) only the current limiting resistor is heating up, not a problen at all if the cathode leg touch the chassis, only permenantly light on LED. But if you connect the resistor to the cathode side and let the anode leg (+12VDC) touch the chassis, you may blow away your PSU.

I think you're pulling at straws here. "But if you connect the resistor to the cathode side and let the anode leg (+12VDC) touch the chassis, you may blow away your PSU" is no different than the positive leg of the resistor touching ground with the resistor on the anode side of the led. Besides, this is what fuses are for.
BTW, welcome to the forums.🙂

 

[DoubleUhat]

Point noted Syberscott, as I assume Cogtx puts every component on a PCB, where only the LED is wired out to some panel, going thru' some metal partition hole, etc. That's why I said anode side not anode leg. Under normal working condition, the jumper wire will be ~1.5VDC and 0VDC vs 12VDC and ~10.5VDC.

Should the jumpers route thru' sharp metal and get cut, shorting 1.5VDC is still better than shorting 12VDC right? And, some PSU have only fuse on the AC primary side, none on the secondary side, and yet the PSU is 50% duty cycle rated. Why take the risk if you can avoide it?

BTW, thanks for the welcome, cheers.

 

[blahblah99]

Originally posted by: CTho9305

Originally posted by: blahblah99
For your application (and many others), there's absolutely no difference.

Ok, you've got me wondering. When is there any difference at all between the order of components in a series circuit?

Well, if it is a sensitive signal, the placement of component 1 before the other component could affect performance of circuit, or vice versa.

As an example, suppose we have two resistors in series going into the input of an opamp. On the other end, we have a low impedance source driving that node. So we have Source->R1->R2->input to opamp. Now let R1 be much lower in value than R2. If there is some crosstalk (or any other unwanted signal) being picked up somewhere along the net between R1 and R2, having this configuration would be a LOT better than having Source->R2->R1->opamp because it provides a lower impedance path to ground.

 

[dym]

I dun think so...
the order of the resistors or leds are just important when trouble happens... (over voltage or current phenomenon...)