at my wit's end

[zachtheterrible]

WHY DOES NOT THIS WORK!?!?!? shouldnt the LED light up?

i know this this question probably has a very basic answer, but for the life of me, i cant figure it out :x :x :x :x :x :x this is so frustrating :x :x :x :x :x how do i get it 2 work?

there is no point to this circuit i know, but it has to do with a different project im working on.

 

[williB]

where ? what circuit?

 

[hotwaterwizard]

A Picture is worth 1000 words.
I guess you are still working on the 1000 word part because I don't see a picture.
Are you just Venting or do you really need some help with your Invisible Project.
Try hooking up the Hot and the Ground.

 

[zachtheterrible]

CRAAAAP!!!! I DID IT AGAIN!!! THATS THE SECOND TIME IN ONE WEEK!!! :x :evil: :x :evil: :x :evil: . i guess i was just distracted by my blinding rage :x

 

[williB]

it should work
what does the current in the diode path read ?

 

[zachtheterrible]

the ammeter part of my multimeter is broken, but the 10A part works. i set it to this and got a reading of .62 thats 62 milliamperes, correct? i tried a bunch of different transistors taht i KNOW work. wat is going on!?!? this is crazy :x

 

[psu_EE_guitar_nut]

yea that should work, could be bad transistor, bad diode. Do you really need the transistor though? A resistor would work as a replacement, 3k should work fine, also with the transistor thiers nothing to limit the current so you may be running in saturation which could explain why no currents flowing.

 

[Oznog]

it should work
what does the current in the diode path read ?

Duh! No it won't. There is no current limiting on either the base OR the LED path, it's hooked right up to 3V. The base of the transistor is destroyed instantly, the LED may be destroyed as well. But some LEDs do not light at 3v, these wouldn't conduct enough current to destroy itself.

Both the base and LED must have some form of current limiting. An emitter resistor could serve both purposes but none is shown. Actually, if you used a base and LED resistor, there would be no point in the transistor at all since it would just stay on all the time.

 

[zachtheterrible]

thank you oz n guitar nut, i thought i was loosing my mind!!( :x )

its kind of funny, i so often don't know the basics. gota do a little refresher

oh yeah, n my LED survived the blow :lol:

 

[Nigel Goodwin]

As Oznog says, it won't work because it will blow the transistor when you apply power. But apart from that it wouldn't work anyway (assuming the power supply was current limited), because there's not enough voltage to light the LED - the base emitter junction of the transistor can't be more than 0.7V, and the LED will get less than that - not enough to light an LED.

 

[gerty]

Zach..If I'm not mistaken,depending on the meter, on the 10 amp scale
.62 would be 620 ma....

 

[lavenatti]

Poof goes the LED.....

 

[kinjalgp]

Zach..If I'm not mistaken,depending on the meter, on the 10 amp scale
.62 would be 620 ma....

Yes it is 620mA

 

[zachtheterrible]

620 ma from 2 AA batteries? that sounds a little high 2 me.
thanx everyone :lol:

the LED still works :lol: , just like new

 

[kinjalgp]

620 ma from 2 AA batteries? that sounds a little high 2 me.
thanx everyone :lol:

Yes it is possile. Just try connecting a piece of wire between positive and negative terminals of the battery. Put your ammeter in between and measure the current that small AA sizeed battery can supply. No doub't you'' destroy the battery in no time. Don't underestimate its power & Never judge things by its size.

I remember once I accidently droped an iron nail onto a fully charged 12V,7.5Ah battery terminals. The battery melted the nail in seconds......

When short circuited batteries can supply hunderds of amperes.

 

[Nigel Goodwin]

When short circuited batteries can supply hunderds of amperes.

Depending on the type!.

Non-rechargable batteries have fairly high internal resistances, but NiCd, NiMh, or Lead Acid have very low internal resistance and can supply huge currents (and destroy themselves!). For this reason they are quite dangerous - the classic story is dropping a large spanner across a car battery!.

But a normal alkaline AA should provide 2 or 3 amps!.

 

[zachtheterrible]

Hate to beat a dead horse, but i finaly got around to getting on this "project".

i'm @ my wits end. this picture depicts EXACLY what i have done. for R1. i have tried 100, 220, 330, and 660 ohms. none worked. and each time i tried a different transistor. wut the devil is going on!?!? This is the LED that i am using: http://superbrightleds.com/specs/g5_specs.htm

The power suply that im using is one of those switchable walwart (i think thats wut they're called) types. its on 3v.

heeeelp

 

[gerty]

Zach.. look at your led specs.. the forward voltage is 3.5v and you are feeding it 3 v..
plus don't forget the voltage drop across your transistor..
edit:
forgot to mention that without a base resisor you are probably shunting the current and bypassing the led ,check voltage across the resistor and if its your applied voltage minus drop across trans that's what's happening..

 

[zachtheterrible]

ahhh, i see. i thought that it would work fine because i can supply the LED by itself w/ 3 volts and it is extremely bright. ill go on down to the garage and up the voltage right now :lol:

EDIT: :x :x :x :x upped the voltage to 9 volts and lowered the resistance to 47 ohms and still, NOTHING!!!!!!

 

[gerty]

did you see my edit above