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How to increase 555 timer output voltage

Discussion in 'General Electronics Discussion' started by peja5081, Jul 21, 2012.

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  1. peja5081

    peja5081

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    Jul 21, 2012
    Last edited: Jul 21, 2012
  2. duke37

    duke37

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    772
    Jan 9, 2011
    How can you increase to 12V when you already have 12V?

    5V should be plenty to drive LEDs, just adjust the series resistors.

    The green LED has a lower series resistance than the red LED. Will the current be too high?
     
  3. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    If you read the circuit description on that page they say there is a 2 volt drop going into the 2nd 555, thus the likely reason for the adjusted resistor value...
     
  4. duke37

    duke37

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    772
    Jan 9, 2011
    I should have read the link. Pin 8 is the power input to the 555 and this is derived from the output of the first 555. Pin 4 is not power input as I assumed, it is reset.
     
  5. Merlin3189

    Merlin3189

    250
    69
    Aug 4, 2011
    I'm not sure that helps. It still doesn't explain why the LED series resistors have a 2:1 ratio.
    A 2V drop from 12 to 10 or even 9 to 7 would not require a 2:1 ratio.
    I can only presume there is an unmentioned difference in the current required for each LED.

    Anyhow, if Peja requires 12V to drive each LED, he can use a buffer transistor with the LED (and series resistor) on the collector, connected between 12V and 0V, with a base resistor to give safe saturation drive.
     
  6. gorgon

    gorgon

    603
    24
    Jun 6, 2011
    The red LED is driven by 12V. The green LED is driven with only 8V(approx 2V drop in each 555). Given that red LEDs drop 1,7V and green LEDs drop 2V+, the current in the red LED is 22mA, and the green LED is around 27mA. To get the same current in both, the 220 ohm resistor should be 270 ohm.

    TOK ;)
     
  7. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    In addition to the differences in LED, it might very well just be what was available to the author...

    For example here is a list of the store stocking ¼ Watt resistor values at Radio Shack in that general area 1K, 470, 330, 220, 100

    Easy to see where the jump from 220 to 470 can arrive if that is all you have available and want to keep it simple and not get into parallel or series resistors...
     
  8. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    LEDs need a defined current drive, perhaps peja5081 could tell us why he needs more voltage.
     
  9. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    My guess is that he/she purchased pre-resistored 12 Volt ready LEDs... There is a big problem with the way these are marketed to the masses... Due to the ignorance of the general population these 12V pre-resistored LEDs all the sudden becomes a "12V LEDs" proper... Most don't have the slightest clue that LEDs are current driven, and only require a minimum forward voltage...
     
  10. peja5081

    peja5081

    2
    0
    Jul 21, 2012
    that's right:p..look like this
    https://encrypted-tbn1.google.com/i...AGAEywUpLknvfY0vO1HXKuSRYeEGeNXTVa6uIYlTQMyKC
     
  11. Merlin3189

    Merlin3189

    250
    69
    Aug 4, 2011
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