Blown Led 555 timer board.

Discussion in 'The Projects Forum' started by Road1, Oct 4, 2012.

  1. Road1

    Thread Starter New Member

    Oct 4, 2012
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    I currently have blown my 555 timer chip that flashes 2 Led's. It works fine from a 9v battery, but burns up when using a 9v 1.5a (1500ma) wall adapter.
    The kit I have comes with the following:
    555 timer
    33k ohm resister
    120k ohm resister
    4.7 MFD capacitor
    2 Led's
    9v battery snap.

    I want to change the 9v battery to the wall adapter without burning up the timer or board. I know the 555 timer chip maxes out at 200ma. I thought the circuit board with the 555 chip would only draw what it needs, but I keep burning them out when hooked up to my 9v wall adapter. What could I add to keep this from happening?
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. ScottWang

    Moderator

    Aug 23, 2012
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    I didn't see the LED current limitation resistor.
    How about the V,I of LED?
    If the surge damaged the NE555, then you can add one R,C to limit current when NE555 power up.
    C - 220uf/25V
    R - according to the current of NE555.
     
  4. Road1

    Thread Starter New Member

    Oct 4, 2012
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    0
    The Led's are rated at 3.2 volts at 25ma max.
     
  5. ScottWang

    Moderator

    Aug 23, 2012
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    You have to measure the voltage of wall adapter, it better be around 9Vdc.

    Now, I'm asuming NE555 limiting at 100mA.
    So, you can add one R(10Ω) and C(220uf/25V) to NE555.

    wall adapter(9Vdc) → R(10Ω/1W) + C(220uf/25V) to GND → from R,C contacts → pin 8 of NE555.

    If you didn't add any resistor to the LED, because the LED is flashing, so you may series a 160~240Ω to the LED.
     
  6. Road1

    Thread Starter New Member

    Oct 4, 2012
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    0
    Thanks for the info. It's been along time since I messed around with electronic circuits and I'm very rusty. I do appreciate the help.
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    you probably need a "regulated" 9V wallwart. Or add a 9V regulator to your circuit.
    I'd suspect this wallwart is unregulated which means that the 9V could be much higher depending on the load on it..

    But yes..This post is worthless without a schematic.
     
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,392
    1,605
    Is this truly a DC output? Some wall warts (about half) give an AC output. And again, the DC outputs aren't necessarily a nice steady DC, some are a pulsing DC, just a half or full wave rectified AC.

    If it is a DC output wart, you have the polarity correct, right? You checked it?
     
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