Direction of flow of electricity through an LED

[Humberto]

Having played with LEDs as a child I am under the impression that they only work when the electricity flows in the one direction.

Some devices have plugs with two pins so that the direction in which the electricity flows is not fixed.

How do they get around this problem?

 

[a'zombi]

Having played with LEDs as a child I am under the impression that they only work when the electricity flows in the one direction.

Some devices have plugs with two pins so that the direction in which the electricity flows is not fixed.

How do they get around this problem?

Electricity only flows in one direction. If we're speaking of Conventional current that is.

 

[Unhappy438]

Having played with LEDs as a child I am under the impression that they only work when the electricity flows in the one direction.

Some devices have plugs with two pins so that the direction in which the electricity flows is not fixed.

How do they get around this problem?

How does the LED get around this problem? With the use of a semiconductor diode

 

[bekdik]

Electricity only flows in one direction. If we're speaking of Conventional current that is.

It only goes downwards due to gravity?

 

[Mr.Jax]

A couple of things require explanation.

First off, L.E.D stands for Light Emitting Diode. The Diode part is the important bit here. Diodes restriction the direction of electrical flow to one direction. From Wiki: "In electronics, a diode is a two-terminal electronic component with asymmetric transfer characteristic, with low (ideally zero) resistance to current flow in one direction, and high (ideally infinite) resistance in the other."


Now, getting an LED to work no matter which direction the electricity flows is actually very simple (one way is to use a bridge rectifier which basically a clever way of "swapping" the flow of electricity around for you..not the real purpose of a bridge rectifier I will add.)

Now getting back to "some devices have plugs with two pins so that the direction....". Please elaborate and I'll answer you.

 

[a'zombi]

It only goes downwards due to gravity?

Hey don't be a bright spark

 

[a'zombi]

He's probably speaking of europlugs i.e two-pin plugs. I'm not sure why he's under the impression that the direction varies. Unless I'm misunderstanding.

 

[Creepster]

Give him a LED with 2 leads thats unidirectional.or one with 3 leads.problem solved

 

[hyarion]

I think what you are trying to say is that when it's a 2-prong plug it can be inserted in 2 different ways, meaning the same "pin" is not always "positive".

My explanation below might be a little bit wrong as I havn't studied electronics, only dabbled, but general concept should be right (I hope):

The LEDs use DC current while your plug points in your house are AC. When it's converted from AC to DC (which is usually where the rectifier mentioned by others comes in) it will only allow electricity to flow in the set direction - so it wont "go the wrong way" in simple terms.

 

[Creepster]

Having played with LEDs as a child I am under the impression that they only work when the electricity flows in the one direction.

Some devices have plugs with two pins so that the direction in which the electricity flows is not fixed.

How do they get around this problem?

only DC has a direction.AC swaps every half turn of the generator.wiki is your friend. USE it...

 

[entrepr]

Some devices have plugs with two pins so that the direction in which the electricity flows is not fixed.

How do they get around this problem?

An LED essential works in a direct current environment, around 3 - 48 Volts, usually 9V or 12V. If you are talking about plugging the 'two pins' into a power socket, there is a power supply in between the wall socket and the circuit board with the LED, which brings down the voltage and also rectifies it to flow in one direction. If the LED is imbedded in a simple device then the power supply can be very simple - an LED with a large resistor, maybe another power diode in series. This is possible because when the AC is flowing in one direction, the LED pulses and when it flows in the other direction, the LED switches off. The results is an 'average' light intensity which your eye detects as 'light on' - the fluctuation is too quick to be noticed.

 

[Creepster]

The most powerfull LED's i know of uses 4.2 volts.I got the 3.7v versions.makes a bautiful flashlight

 

[Cyberdude]

If you connect the LED directly to your 2 pin AC socket it will work as the current flows through the LED in the right direction for half the time. But don't try this at home! Oh and the LED might be a bit brighter than usual and won't last very long.

 

[chrisc]

 

[Archer]

http://en.wikipedia.org/wiki/Rectifier#Full-wave_rectification

That should explain it all for you. The pos/neg AC sine wave gets rectified into an always positive sine wave (edit: regardless of how its plugged in). Add some capacitors and you can smooth the sine waveform into (essentially) a constant voltage

 

[Creepster]

If you connect the LED directly to your 2 pin AC socket it will work as the current flows through the LED in the right direction for half the time. But don't try this at home! Oh and the LED might be a bit brighter than usual and won't last very long.

DID it.Think i got iradiated by photons.I see glows in da dark

 

[Moosedrool]

http://en.wikipedia.org/wiki/Rectifier#Full-wave_rectification

That should explain it all for you. The pos/neg AC sine wave gets rectified into an always positive sine wave (edit: regardless of how its plugged in). Add some capacitors and you can smooth the sine waveform into (essentially) a constant voltage

Well yeah but calling it a always positive sinewave isn't really valid its more like U=|A*sin(t*C)| C as a constant depending on deg, rad or Grad. A Amplitute.

Basically an "absolute of a sine wave"

Also a basic led configuration:

 

[Archer]

Well yeah, but it would seem that the OP doesnt have an in depth knowledge of electronics so maybe it a better idea keeping stuff simple eh?

PS - absolute means always positive, which is what I said... so I'm not sure what you're trying to explain actually

 

[ponder]

Well yeah, but it would seem that the OP doesnt have an in depth knowledge of electronics so maybe it a better idea keeping stuff simple eh?

/waits for someone to post electron hole theory with some dirac equations thrown in

 

[Moosedrool]

Well yeah, but it would seem that the OP doesnt have an in depth knowledge of electronics so maybe it a better idea keeping stuff simple eh?

PS - absolute means always positive, which is what I said... so I'm not sure what you're trying to explain actually

Nothing big it's just my opinion of an always positive sine wave is the blue line:

Unlike an absolute sine: