Question regarding LED fading circuits.

Discussion in 'General Electronics Chat' started by Jakal999, Oct 24, 2016.

  1. Jakal999

    Thread Starter New Member

    Oct 24, 2016
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    Hello all,
    I'm a DIY'ER and wanted to know if there is any advantage or benefit between a 555 LED fading vs. an LM358 LED fading circuit. Is one better than the other? I've also built one with a PUT transistor as shown in my Make Electronics Manual, but I'm aware that those are long obsolete. Thanks ahead of time for any input you have.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Welcome to AAC!
    If it works, it works.
    'Advantage' can take several forms: cheaper, fewer components, components you already have in your junk box, lower current consumtion, able to work from higher supply voltages, .......
     
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  3. Jakal999

    Thread Starter New Member

    Oct 24, 2016
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    Thanks, so in the end, I'm guessing it just comes down to what you have on hand and what you like best? I didn't know if one component was better designed for the circuit than the other. You are however right, "If it works, it works". And they all get the job done... :) Thanks again Alec_t and if there is any other input I'm all ears, or eyes rather shall I say...
     
  4. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    Since you are keeping all of the circuit details a secret, it's kinda hard to do anything but guess.

    IF by "555 fading" you mean a switching regulator or pulse width modulation circuit
    AND IF by "358 fading" you mean a linear regulator or linear, variable current source
    THEN one difference between the two is power dissipation.

    A PWM dimmer can be 90% efficient, while a linear regulator can dissipate significant power if the source voltage is much greater than the LED voltage.

    ak
     
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  5. Jakal999

    Thread Starter New Member

    Oct 24, 2016
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    Thanks AnalogKid, I know my question is rather broad as I'm sure you may know of several ways to accomplish a fading LED with both IC'S. When I search for fading LED circuits with either of the two using just the IC, some resistors, a couple capacitors, hook up wire, a transistor and a power source, most sites show pretty much the same schematic from what I can see. I'm fairly new to this and was just doing some basic bread boarding. I did notice that the 555 circuits usually required 9 volts where the LM358 circuits that showed up sometimes required less voltage. I just became curious after building the two circuits. Bear in mind this just using those components listed earlier, nothing else, where the LED fades up and down constantly. No push buttons nothing else. Sorry for any confusion or frustration. I think "Alec_t" hit it on the spot. I will learn in time and possibly return with a better stated question. Thanks guys.
     
  6. ian field

    AAC Fanatic!

    Oct 27, 2012
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    PWM is the way to go and you can do that with a 555 or a 358. A bipolar 555 can shift 200mA - so its good for the bottom end of the power LED range. The LM358 dual op-amp or the LM393 dual comparator can just about drive a 20mA LED directly without adding an external transistor.
     
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  7. Jakal999

    Thread Starter New Member

    Oct 24, 2016
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    Hey thanks "ian field", that really helps and I have a pretty good grasp on what your explaining. And so it seems that the LM358 could quite possibly be the more simple (less components) method to creating the circuit. So I'm seeing some advantages in the dual op amp route ie. Power versatility and simplicity. Which would probably explain why all the Ebay fading LED DIY solder kits ("breathing light kits") from all over are LM358 IC based. Thanks.
     
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