Any engineering Geeks here? LED torch query

jamoor

jamoor

jamoor

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How does an LED torch that take AA batteries work exactly/

IIRC an LED has to have a +ve and -ve feed, however the batteries -ve feed are at the bottom of the torch, so how do the LEDS light up?
 
Doesn't matter where in the torch the negative end is as long as it completes the circuit. Same with any electronics.

Also, they don't need a positive and negative feed, LEDs only light when current is travelling through them one way (usually considered the positive direction), which is why under an AC circuit an LED would flash, only lighting on the positive cycle.
 
The - terminal probably has a connection to complete the circuit running through the case of the torch so once the bottom is screwd on a contact from the bottom of the casing hits a contact on the terminal thus completing the circuit
 
$qu!ff said:
The - terminal probably has a connection to complete the circuit running through the case of the torch so once the bottom is screwd on a contact from the bottom of the casing hits a contact on the terminal thus completing the circuit
Click to expand...

^^

There's usually a bullseye like contact. The centre part of the contact touches the nib of the AA, and the outer ring makes contact with the case of the torch (which is connected to the -ve terminal of the batteries).
 
LEDs are fun fun fun. You can buy a bag of 'em for a couple of quid from places like ******s etc. A variety of colours too. Flashing LEDs too. Only one rule - they only trigger beyond a threshold voltage which is significantly higher than the usual 800mv needed to avalanche a standard semiconductor depletion layer. Only one other rule - too high a current will fry them and possibly start a fire...

To vary the intensity you vary the in-line resistor. The lower the resistor the brighter and vice versa or you achieve the same by varying the power source voltage. With a couple of wires, soldering iron and the hitchhiker's guide to resistor values (BBROYGBVGW)(0123456789)(plus knowing how to figure out resistor multiplyer bands) it's possible to wire up anything you care to. Flashing cat-flap indicator, ashtray lid-open indicator, bonnet closed flasher, granny forgot to put out the cat indicator.. The list is endless...
 
You do realise that being -ve, the current flows through it in the other direction to the +ve, ie out of the -ve and into the +ve (taking current as -ve charged electrons).

Jokester
 
Jokester said:
You do realise that being -ve, the current flows through it in the other direction to the +ve, ie out of the -ve and into the +ve (taking current as -ve charged electrons).

Jokester
Click to expand...

The still implies one is a feed and one is a return ;)

Edit: Oh, and there was no indication of current flow originally!! Woohoo, pedant's argument!
 
jaydee said:
To vary the intensity you vary the in-line resistor.
Click to expand...

I thought LEDs are either on or off.
dunno.gif


wikipedia proves me wrong :o
 
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You're right, it doesn't, but current "flow" indicates direction and as such a battery can't have both a +ve and -ve feed, but it can have +ve and -ve terminals!
 
Jokester said:
You do realise that being -ve, the current flows through it in the other direction to the +ve, ie out of the -ve and into the +ve (taking current as -ve charged electrons).

Jokester
Click to expand...

The movement of electrons is from -ve to +ve yes, but a conventional current flow is happy enough stated as flowing from +ve to -ve as you have the same number of proton charges moving.
 
Ok, assuming electron flow, current flows out of a negative feed.

Now looking at the positive feed, it flows into it.

They're both compatible.

Jokester
 
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