7555 power consumption

Discussion in 'The Projects Forum' started by tibbles, Jul 28, 2008.

  1. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    to cut a long story (fairly) short, i have built a circuit the output stage of which is a 4013 d type triggering (at long intervals days or weeks) two 7555s configured as flip flops, each lighting an led. sinking.
    the circuit works well (surprise surprise) my concern now is that the 7555s in quiescent standby mode are consuming .2 amps (as against the spec of 80 micro amps) ,not much i know, but i have limited space for batteries, so i would like to know if anyone has looked into this before or has any thoughts on this.
    i have checked the 4013 (negligible consumption) and the 7555s peripheral componants are not taking any power.
    maybe a complete power off of the 7555s somehow, between trigger pulses ?

    regards
    dougal


     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Dougal,
    It would help a great deal to post a schematic of your circuit.

    Right now, I would have to assume that you have VERY large capacitors and very small resistors used as timing components - which will result in a hefty current draw.
     
  3. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    thanks Sjt
    i am using the 555s as standard flip flops so there are no RCs, only a 1UF electrolitic from pins 6 and 7 to neg ,forming the push button reset.
    and a differential diode/resistor set input to pin 2 ,
    the 555 is doing nothing most of the time so i would have expected the quiescant to be pretty low,


    (i have tried to copy and paste circuit into post window but didnt work)
    regards
    dougal
     
  4. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    ps
    current drops to almost zero when i take out the 555s
     
  5. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    are consuming .2 amps

    sorry, just read my post again. should read .2 milliamps
     
  6. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    problem solved i think, with surprising results.
    i have been testing with a nine volt battery ,well the pp3 is a gift.... and getting a drain of over 1 milliamp for the whole circuit( 6 chips)on standby ,but tried a 6 volt battery( which is the designed voltage)and the current dropped like a stone to about .3 milliamps !
    again that might not not sound much but should treble the battery life,

    thanks again
    dougal
     
  7. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    just ready to put the lid on this one,, end on a puzzler.... snipped an led on the test circuit, immediately the quiescant current dropped from .08 ma to almost zero.
    so even when "off" the leds are taking significant current
    any thoughts or suggestions welcome
    regards
    dougal
     
  8. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    please ignore last post, tried it on completed circit made no difference.

    regards
    dougal
     
  9. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    out of curiosoty ,if anyone hasent already done this, when i get a minute i will rig up a 7555 as a flip flop bistable and do a direct test anyone care to predict result?
    dougal
     
  10. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The datasheets for the LMC555 and the TLC555 lists typical and max operating current at 3 different supply voltages.
     
  11. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    just done a quick test on a bread board
    65micro amps @6volt
    70 microamps @ 9 volt


    but overall a complete success, the original 1.1 milliamps drain for the whole circuit has been reduced to just under 200 microamps by dropping the battery voltage from 9 volts to 4.5 volts.
    the circuit works fine, i would have expected to reduce the led resisters but no need, hardly any difference in brightness,and 3 AAA batteries in a flat pack take up little more space than pp3.
    well thanks for your help everyone and i hope others might find this useful.
    regards
    dougal
     
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