Circuit's IC getting hot

Discussion in 'General Electronics Chat' started by fehaan, May 30, 2014.

  1. fehaan

    Thread Starter New Member

    Jun 10, 2011
    9
    0
    Hello,
    I tried a circuit from this link for my generator.
    http://www.electronicsforu.com/elec.../cir15.htm&title=Add Auto Start To Generators

    After fixing everything on PCB and testing on 9volt (FF2) battery the whole circuit performed fine as it should be.

    cross checking everything, and re-testing after enclosing the circuit in a secure plastic box, I went to finally connect it with the generator.

    when I connected it with the Generator's 12v - 45AH battery, the circuit didn't stop counting (which it should after 5 tries). The 4017 IC got very hot too.

    I am unable to find out what made the IC to become hot, and why did the Transistor didn't switch the counter IC to OFF position? Before that the circuit worked all correct.

    can anyone guide me?... was it because of the Battery's ampere...?
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,364
    A battery's AH rating would not affect the operation of the circuit.
    CMOS chips are prone to a destructive phenomenon known as "CMOS latchup".
    This is most likely the reason why the 4017 got hot.
    There are a number of precautions required to be taken to prevent CMOS latchup.
    The most important precaution is to protect all input pins and ensure that the voltage on any pin does not fall below VSS and does not rise above VDD.
     
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  3. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
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    Maybe static charges helped.
     
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  4. crutschow

    Expert

    Mar 14, 2008
    13,042
    3,243
    CMOS ICs can get hot if any of the unused inputs are left floating. Make sure they are all connected to ground or V+.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The schematic does not show any bypass capacitors, however they are required for proper operation. Each IC needs a minimum of 0.1uF/100nF poly metal film or ceramic bypass capacitor across it's Vcc/GND leads, and the 555 timer also needs a 1uF electrolytic or larger across it's Vcc/GND leads. These are NOT optional!

    Bypass capacitors are frequently omitted from schematics for clarity's sake, as it's common knowledge that they are required. The requirement for bypass capacitors is frequently difficult for beginning electronics enthusiasts to understand. We wouldn't tell you to add these unless they were necessary; and if you use IC's, they're necessary.

    When bypass capacitors are not present, circuit operation is "glitchy"/intermittent at best, non-functional at worst.
     
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  6. fehaan

    Thread Starter New Member

    Jun 10, 2011
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    thanks for your reply. Can you further guide me on how to introduce bypass capacitors to all ICs / wherever necessary by showing on the schematic?
     
  7. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,812
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    Bypass capacitors should be connected as close as possible to the Vcc and Gnd pins of the IC.

    If this is your schematic, I've inserted the capacitors at the highlighted locations. Note the different values for the 555 and the CMOS logic.

    [​IMG]
     
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  8. SgtWookie

    Expert

    Jul 17, 2007
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    Thanks for getting the mods to the schematic done; I've been swamped here at home lately.
    AND the length of the capacitor's leads should be as short as possible to minimize their inductance.

    I failed to explain earlier that it's mainly the inductance of the wiring between the power supply and the IC's is why the capacitors are necessary in the first place. Rapidly-changing signals (like with digital logic) will cause non-bypassed supply busses to "ring" like the dickens. Bypass capacitors of appropriate sizes will "swamp" that effect, similar to throwing a hissing garden hose nozzle into a bucket of water.
     
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