Author Topic: Noob question from from electronics tutorial w/LED & resistors  (Read 3623 times)

invis

  • Newbie
  • *
  • Posts: 1
Noob question from from electronics tutorial w/LED & resistors
« on: November 30, 2014, 05:49:19 PM »
Hi,

I have been watching MJLorton's intro to electronics videos, and I have to say you/he describes things in a way that I actually seem to be able to grasp. I'm a software guy, but I've never really been able to get a handle on hardware. I've had lots of people try to explain things to me and I've read a bunch of things on it, but these videos seem to work for me.

I apologize for the silly question, but, I'm curious:

In the video, there was a ~2v@20mA LED running from a 12v supply using a resistor in-line to drop the voltage and current to the correct specs. I understand that and why. My question is, what if you had a 12v power supply capable of pushing say 20A and you had a 12V LED only rated for 20mA. Would you have to use a resistor to maintain the proper current rating, but that would drop the voltage below what the LED is supposed to be run at? So, would you just run the LED straight off the 12v line with no resistor and count it wouldn't draw too much?

Also, does the position of the resistor matter? Voltage on one side of the resistor is different than on the other side, right? So, putting the LED first in series and then the resistor limit current, but give you a higher voltage as opposed to putting a resistor then the LED for lower voltage AND current, not just current? Sorry if that doesn't make sense, this field being so new to me makes it hard to articulate my thoughts and questions.

Once again, sorry for the silly question everyone. Thanks.
« Last Edit: November 30, 2014, 06:12:12 PM by invis »

birrbert

  • Full Member
  • ***
  • Posts: 149
Re: Noob question from from electronics tutorial w/LED & resistors
« Reply #1 on: December 04, 2014, 05:31:56 AM »
Hi invis!

I'll try to answer your first question since when I began learning electronics I had very similar dilemmas. First of all, let me state that LEDs rated for 12 V / 20 mA are not common; as a matter of fact I'm not sure if they even exists, but for the sake of the example let's assume that they do. So, if you had a power supply which is able to output 20 Amps at 12 Volts and with that you powered an LED rated for 12 Volts and 20 mA then you don't need a resistor. This circuit is fine with no additional components, because the LED draws as much current as it what it wants to draw at 12 Volts; and since it draws only 20 mA from a power supply that could handle even 20 A, there's no problem. It's worth mentioning that if a power supply can output a maximum of 20 A that doesn't mean that it will output that amount of current no matter what; so you don't need to be afraid that your poor LED will get 20 A pushed through it.

I stop here regarding this topic and if you have questions then please go ahead.
"Dubito ergo cogito, cogito ergo sum." Descartes

TechJunkie

  • Full Member
  • ***
  • Posts: 111
Re: Noob question from from electronics tutorial w/LED & resistors
« Reply #2 on: December 08, 2014, 02:47:23 PM »
I whipped up a quick circuit simulation for you using a 12DC power source, switch, LED, Resistor and DC Motor. Take a look at the simulator values and you will see that using a resistor to limit current is all that's needed across a 12DC source. I assumed a typical Blue LED with a forward voltage drop of around 2V. Hope this helps! Sorry, don't have time to get very detailed but if you have further questions feel free to ask.
Eric Haney
Systems Programmer, EE, MCSE, DMC
SilverCore Labs

Pitbull603

  • Newbie
  • *
  • Posts: 1
Re: Noob question from from electronics tutorial w/LED & resistors
« Reply #3 on: March 25, 2015, 11:35:47 PM »
What software is that?

Beothern

  • Newbie
  • *
  • Posts: 2
Re: Noob question from from electronics tutorial w/LED & resistors
« Reply #4 on: August 26, 2015, 04:25:23 AM »
The information I have from you is a great gift for me.

EmilyBrown

  • Guest
Re: Noob question from from electronics tutorial w/LED & resistors
« Reply #5 on: May 22, 2018, 06:44:31 AM »
Thanks for sharing electronics tutorial with us.