Why does the simplest LED circuit work without a resistor? #shorts

This is the simplest LED circuit possible -- a single LED connected to a coin battery. Have you ever wondered why this circuit works? Where's the resistor to limit the current?

There are two factors making this basic LED circuit work. One, LEDs have a parameter called forward voltage (Vf). If the supply voltage and Vf match or are close enough, the LED will work without a resistor because the voltage is not high enough to cause a critical amount of current to flow.

In the video I show a blue LED, which has a Vf of 3V, connected to a 3V supply and a 3V battery without burning out.

Secondly, coin cell batteries happen to have a high internal resistance. This acts like a resistor in series, thus limiting the current. The coin battery's internal resistance is the reason why it powers a red LED (Vf=1.8V) just fine. However, that LED burns out moments after it is connected to a pair of AA batteries (3V), which have a much lower internal resistance and push too much current through the LED.

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#DIY #electronics #LED
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[mondude]

When I was younger I never even knew that you were supposed to use a resistor and always connected the LEDs directly and they didn't really burn out

[charliethiede]

Oh that’s why I keep blowing out these leds😂😭

[jimvodraska]

I agree. At a low enough voltage (call it a threshold voltage, which has to be higher than the LED's forward drop), it will light dimly. As the voltage increases, the current will increase and the LED will be brighter. At a certain point, the current will get too high and damage the diode chip.

[planktonfun]

My first thought was battery has its own ohms, glad my hunch was right!

[NLRevZ]

This brings back memories of the LED throwies... People used to make absolute loads of these using LEDs with builtin blinking ICs, tape each one together with a strong magnet and throw them all over the place onto metal bridges and overpasses and whatnot. It was fun!

[ExploringNew]

Small LEDs used to not burn out even when I was using a 500mA 12V wall adaptor supply to power them just because I didn't know that. But now that I know how circuits work, I keep blowing leds up 😭

[jimvodraska]

If the battery voltage is low enough to just light the LED, but not damage the chip, it works.

[Drxxx]

Try both in parallel (red and blue) without resistor. Afrer that, you will be always using the resistors in your circuits

[jhuff]

Once wired my gate opener remote to my car. Luckily that remote used a small 12v battery so the 12v from my car was perfect.

[dean-phww]

Seeing those resistors connected like that reminds me of my old job at the circuit factory filling orders. We had a bakers dozen policy. One freebie for every 12 ordered.

[slabua]

I've never used a resistor with leds in almost 30 years

[ecmjr]

I learned something new today, thanks!

[phil]

"Forward voltage" is basically the voltage the device is rated for. If you use a constant voltate power supply that matches this voltage, or is just under (for a little more dim), then your LED just pulls as much current as it needs without exploding.

If you add a resistor into the circuit, you have turned a constant voltage power supply into both a constant voltage and constant current power supply. This means the voltage across the LED matches its forward rated voltage, and the rest drops across the correct tesistor, as well as only leaving a certain amount of current left over.

[Sir_Cactus]

Be careful when using LEDs. The formula U=R×I does not apply on them.

[Scrogan]

If you leave that PSU on 3V connected to the LED, you may well enter the domain of thermal runaway.

[petrlaskevic]

Very interesting! Could you please make a full video on this?

[atlantis]

i once stuck a white LED into a powerboard when it was a little kid, there was a bang and some smoke but nothing more

[santi]

LEDs behave like NTC thermistors, so his internal resistance will drop when it warms.. LEDs Always needs a limiting resistor no matter the power source.

[corpedononeseperoidocrop]

in simple words:
I=V/R
where I is the current
V is the voltage
R is the resistance
now 3/(typically 250) = 0.012 AMPERES, and an led can simply handle that

[burt]

What voltage is the red LED rated for? I'm assuming is for lower voltage than the blue one