555 Timer broken?

Discussion in 'General Electronics Chat' started by MWG, Aug 13, 2009.

  1. MWG

    Thread Starter Member

    Apr 15, 2009
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    I built a PWM controller based on a circuit supplied by Sgt. Wookie (see attatched)

    I've finally gotten round to putting it all together and had it running briefly, i then added in a fuse and a couple of LED's and now its stopped working!?

    all the components seem to check out ok, i put a 12V source directly to the gate on the IRFZ46N and i get a 12V output so i assume the 555 has had it

    i put a multimeter across pin 3 and ground and there was nothing, i also tried to read the frequency but it read 0

    Any suggestions as to what i can try and to why it failed?

    Thanks
     
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  2. mik3

    Senior Member

    Feb 4, 2008
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    Is the fuse ok?

    Where you get the 12V from?
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Check your transistor, especially the input. If it is shorted that would kill the circuit. Are you using a protoboard?

    You might also link to the original thread.

    If the 555 is in a socket you could try something like the 555 Hysteretic Oscillator
    as a 555 tester.
     
  4. MWG

    Thread Starter Member

    Apr 15, 2009
    28
    0
    fuse is fine, i even tried bypassing it altogether and the chip is definitely getting 12V in

    power is from a DC adapter that you plug into the wall and before anyone asks, i have tested it and it works fine
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Do you measure 12V across the adapter or more?
    In other words, is it regulated or not?
     
  6. MWG

    Thread Starter Member

    Apr 15, 2009
    28
    0
    i have all of the components on a stripboard and wire instead of using the traces as its supposed to be carrying 11A

    I think i may have found a problem with a short between pins 5 and 6, would that kill it?

    original thread is located here

    Edit: its ~12.5V out of the adapter, no idea if its regulated or not, its for a rechargeable AA battery charger i have
     
  7. Wendy

    Moderator

    Mar 24, 2008
    20,766
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    It would kill the circuit, but it shouldn't kill the 555 I think. Pin 5 shorts to ground the same time pin 3 does. Since pin 6 in this circuit is an input, the circuit would quit working, but after the short is removed it should start working again.

    If pin 5 is ever connected to the power pin then death is quick and certain.
     
  8. MWG

    Thread Starter Member

    Apr 15, 2009
    28
    0
    2 seconds with the old dremel and its now working again :D

    apologies for wasting your time fella's

    thanks for your help, much appreciated
     
  9. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    I see you have added some LED's to the original ckt. R6 is too low of a value. I calculate about 45MA to the LED. I would go with at least a 680Ω, for it. I would do likewise for R5. Even thou LED's have a maximum current I find them to be very visible at 1/2 of their maximum current.
     
  10. MWG

    Thread Starter Member

    Apr 15, 2009
    28
    0
    both of the LED's are super bright, and if i'm honest a bit too bright lol

    the Red has a max voltage of 2.6V and a max current of 50mA,

    as for the green the max V of 3.8V and max current of 30mA
     
  11. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    Sorry for my error, you have it under control.
     
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