LEDs and Forward Voltage | Basic Electronics

LEDs are really cool.

They have low voltage, low power.

They last a really long time.

and they are really physically tough.

They're not like incandescent.

That's why we have that filament that you bump and it breaks and also burns out you don't have mercury like you do in the fluorescent light switch if you break becomes a huge mess and with halogen, it's so hot that if you touch it, you'll not only burn yourself, You break the light bulb.

So, LEDs in almost every way are fantastic.

But they are different.

You have to work with them a little bit differently and you can still break them if you treat them wrong.

So today, we're gonna look into how to use LEDs and we're just going to use some of these standard LEDs to go over to concepts and then from there, you can extrapolate into bigger or smaller LEDs.

So, right here, I have a couple of different LEDs.

I actually have white, blue, green and red and we're going to talk about the difference in the voltage level of those and how the forward drop is different for those and also just how they work in general.

So, LEDs are light emitting diodes.

So in essence, they are diodes that just happen to produce light at the same time.

So, on all of these they are hooked up in a very specific way.

If you flip them, they're not going to work and that's true with any LED because diodes are one direction only.

LEDs are actually pretty straightforward because I have an extra one right here, They give you some clues on how to tell the difference.

You notice, one of these is longer than the others and then if you actually look inside which you can't look inside all of them but if you can look inside, one of the sides is significantly bigger than the other.

So, the short lead goes with the big side which means it's the negative terminal.

So, in this particular one, current will flow from this side, the longer lead, through out to the shorter lead.

If you put it the other direction, it's not going to work.

Since LEDs are diodes, the voltage and current relationship is not linear.

It's not like a resistor where as you increase the voltage, the current goes up linearly.

What happens with the diode and LEDs is that you increase the voltage, you increase the voltage and no current flows And then you hit a certain point where you get to that forward voltage that the LED starts to conduct and then a tiny increase in the voltage drastically increases the current until basically you overcurrent the LED and it explodes which I'm hoping to do in a couple of minutes.

So, as I mentioned earlier these LEDs with their different colors have different forward voltages because they're based on different semiconductor materials.

So I'm actually going to use this voltage supply and increase the voltage slowly so you can see as they turn on and then see also as the current goes up and as I do it, I'll probably have to take some out so they don't blow because the green and the red with their lower forward voltages will actually probably explode before the white and the blue even start to show any light because they have significantly higher forward voltages.

So let's do that now.

So here, we have the LEDs hooked up and they're being directly driven I don't have any resistors in there, which is not normally something you want to do But we're just doing this for demonstration's sake.

So I'm not expecting anything until we get over 1.

5 volts.

Before we will see even a flicker.

So as we jump up to one, there is still nothing whatsoever.

Now, I'm at 1.

3 I think I just saw it turn on.


If you look, you can see it flicker at 1.

7, 1.

8 volts on the red.

Still nothing on the green that I can see.

Oh, actually there is.

It's just very dim.

As we get up to now a 1.

9 I can see the green better but still nothing from the white and the blue.

We're currently at also Fluctuating between 8 and 15 milliamps.

It's obviously brighter.

There's no question that these two are on.

Still absolutely nothing from there.

Now, these are rated to only be able to conduct about 20 milliamps before you start to cause any damage.

That doesn't mean they're gonna explode if they're at 25 milliamps but anything over 20 milliamps will shorten the life and technically could explode but that's not likely.

They can usually take quite a bit more before you have any catastrophic immediate damage.

So let's keep going up just a little bit more So now we are at almost 40 milliamps.

So these are probably both about at their limit of how bright they are and the voltage you can put across them without any damage.

And notice we're only at 2.

25 volts.

And again, these haven't even started.

So I'm gonna unplug these so we don't damage them right now and we're gonna see what we have to do to get the blue and the white up solo.


2, 2.


Okay, I just saw the blue flicker on At about 2.

3, 2.

4 ish and the white also.

So, white and blue have very similar forward voltages and to get them to about the same forward current, you're actually closer to 3 volts.

There we go.

We got 3 volts and now we're doing Oh 20 actually We can go higher 3.

2 volts and now there's about 20 milliamps going through both of them and is also pretty bright.

So that just shows you different chemistries inside different semiconductor material causes them to conduct at different levels.

If we still had these other two plugged in at this voltage, there would be some serious damage.

And again, we're gonna do a demonstration I've only seen an LED blow up once I want to do it again because it was interesting.

One other thing while I have this is LEDs compared to the other lights, are much more directional.

So from my angle looking down on it, the white LED is enough to kind of give me some stars But it's not nearly as bad as if I bring my face right in front of it which is just blindingly bright.

Now, LEDs have that focus like this Unlike incandescent switch are more like that but you can get LEDs that have a little bit wider viewing angle.

So it depends on what you're trying to do, depends on what you want.

We have a Christmas tree that we use and we put up LED lights and the problem with that is my wife puts up so many LEDs that it doesn't matter where you are, there's at least one pointing directly at your eyeball at all time.

So that is definitely a drawback in certain circumstances.

But other times, you don't want to waste light putting it in all directions and you do want it directly where it is.

So, it depends on what you want, but just know that in general, LEDs are much more focused and in their viewing angle.

So, look into that see what you want to do.

Okay with that.

I'm going to turn this off and I'd actually now like to set it up so that we are going to drive just one red LED and see what happens.

So, I'm gonna put that together really quick.

Okay, so I just set this up.

I actually put this back here for better contrast so you can see it better but we have the LED that's going to be driven directly by this power supply and I've also been using the multimeter to get a more precise reading on the voltage.

But I think we're ready to go to see what happens as we turn it up.

Hopefully it's interesting, visually and hopefully it doesn't hurt me.

With that in mind, I actually do want to grab some safety goggles because I like my eyeballs and even though they're not incredibly fashionable, It's better safe than sorry.

So let's start cranking this thing up.

and we know that it starts conducting at 1.

7 volts All right.

We're at 1.

7 and there we go.

Now I'm starting to see some current flow.

We're getting close.

There we are.

We are now over the maximum recommended value.

And again, just even at this, this will decrease the lifetime Even though, there's nothing catastrophic going on right here.

But let's see what it takes to get up to catastrophic levels.

Let's crank this thing up.

We're now at 3 volts and we are almost four times the current that is supposed to be through there.

I think I want to lean back just a little bit.

I am surprised at how long this is lasting.

So, we are now at a hundred and ten milliamps.

This is being driven about six times more current than it is rated for and we are almost to four volts.

It doesn't even look like it's getting any brighter.

This is really interesting.

I'm wondering if this is ever going to explode or if it's just going to fail and not do anything.

Too interesting.

So we're at 160 milliamps.

This must just be a really tough LED because the other one did not take nearly as much voltage to explode 150 milliamps.

Now I'm just highly impressed.

Oh, but now it's just dead.

So if anything happens, if it explodes, it's because it's too hot because right now we're getting 150 milliamps through there.

So it is probably burning things even though there's absolutely no light being produced anymore.

So, I'm smelling something.

Something is definitely cooking.

I do not want to start a fire in here.

Explosions, I can handle.

Fires, not so much.

Wow, I don't wanna get my face too close to that.

But I'm thinking that it's just melting on there.

Oh, I have a thermometer.

Gary lent me a thermometer.

Let's see how hot this thing is.

Turn that on, see how precise this is.

81 100 degrees 107 degrees 95 104 degrees So, yeah that got pretty hot it did not explode like I was expecting but it got really hot which is kind of a bummer I kind of wanted it cook, wanted it to explode but as you can see it, it did fail.

So I mean it doesn't work anymore.

Had all these.

What the heck it's working again.

I don't even know what to say.

I have no idea what to say.

LEDs are super tough.

This is fantastic.

And my whole experiment did not go as planned, but I think I'm ok with that.

Even though an explosion would have been nice.

Okay, so I'm just gonna turn this off.

I'm not gonna push my luck.

And I'm hoping that it doesn't like explode from the heat behind me and get me in the back of the head somehow.

And again really an explosion, is it just cracking and sometimes it pops pretty far away and frankly again, I've only seen one explode once and it did go a couple of feet.

But it's not gonna actually hurt you unless it hits you in the eyeball.

So, that is the LED.

I think I've rambled on far enough.

You've seen how tough it is.

You've seen the different forward voltages.

You've seen, well, I guess you couldn't smell it Like I couldn't I'm gonna take no I'm gonna leave these glasses on.

because I still don't know if that's gonna pop.

Yeah, it took a lot of current and it started to melt started to smell bad, but it was great.

So I hope that gave you an idea of what it is like to deal with an LED and hope you found this interesting.

I'm sorry.

I wanted to give you guys an explosion something to see, something exciting but this LED is just too darn tough.

If you liked this video, please like it on YouTube And subscribe to our Channel.

And you can go check out our other tutorials at circuitbread.

com As it is.

Have a great day.


Leave a Reply