What could be wrong with my led light box?

Hey you guys I did everything correctly but its still not working. Here's a pic of mine. I know its not the leds because they light up when I plug them up to a 12v source.Also thats a brand new tip31 and im using 8 Triple A batteries?

Picture of What could be wrong with my led light box?
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iceng4 years ago
Re-drawn and if 12V battery that 100 ohm resistor increases to 350 ohms.

With the darlington  configuration a 1uF capacitor in series  with the signal will also work !

tramont (author)  iceng4 years ago
do i really ned to buy another transistor
iceng tramont4 years ago
No you don't, but do follow steveastrouk's advice !

You non-EE people should know how we buy parts.
  • One to Smoke
  • One to Lose
  • One to Use
  • One for the second version
  • One for another reason
  • And add 10% for good measure
Get at least SIX next time.
tramont (author)  iceng4 years ago
Okay but does he want me to put a 100ohm resistor on each led? Also how would I go about wiring that up
iceng tramont4 years ago
Here is the circuit that Steve described.
a gain.gif
iceng iceng4 years ago
Oops one correction change the 47K to a 4.7K ( yel-viol-red ) resistor
tramont (author)  iceng4 years ago
Im only using 6 leds, so is it still wired the same?
iceng tramont4 years ago
Which six ? ...... :-)
a6 gain.GIF
Why are you using a 40 watt transistor when a 2N3904 1/2 watt will do?
Also you need resistors you may have connected this up and the LEDs flashed once and died from to much current.
And he only acquired a single one ! ...................... :-P
I buy from here,


I can get 100 transistors for the same price as five at Radio Shack.
Diodes in backwards ?
No base resistor ?

Take a resistor (4k7 will do), and connect it to the base of the transistor and the 12V supply. The LEDs should light. If they don't, mak sure they are the right way round. If they STILL don't light, you have a dead transistor.
+ you may have too many LED in series and a transistor forward forward drop to light up.
Hmm. Yes, 6, and on 12V.

Try 3 in parallel with 3 and put a 100 ohm series resistor in each leg
tramont (author)  steveastrouk4 years ago
Okay im going to try that thanks for your help
Wot, no current limit resistor ?
Late night muddy brain non-engaged :-)