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DC to AC using a 555 chip

Discussion in 'General Electronics Chat' started by Warlord_1011, Dec 20, 2009.

  1. Warlord_1011

    Warlord_1011 New Member

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    hi all, looking at a trying to convert 15VDC to 15VAC using a 555 timer, i have calulated using this diagram

    [​IMG]

    i have calulated using this diagram:

    R1 = 200k ohm
    R2 = 20k ohm
    C1 = 0.1mf/uf

    points to note, the capacitance in the forumla is actuall in C*10^-6 to get the correct frequencey,

    Now would this circuit be able to create 15vac at 60hz, no different to 15vac from a 240vac to 15vac transformer?

    or would it output 15VDC at 60hhz?
     
    Last edited: Dec 20, 2009
  2. KMoffett

    KMoffett Well-Known Member

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    It only puts out pulsating 15VDC, not 15VAC. What are you trying to do with 15VAC?

    Ken
     
  3. Warlord_1011

    Warlord_1011 New Member

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    i want to make a Christmas lights Tester, althought they run off of 240 ac Mains, i want it to be a bit safer than that, and i basically need to test the bulbs (they are old bulbs with a filliment NOT leds), and im also still rellevtively new to electronics especially IC's, and i wanted to experiment to get more of an understanding
     
  4. dave miyares

    Dave New Member

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  5. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    There's really not much difference, and feeding it through a simple capacitor removes even that difference.

    That's always the question.
     
  6. Warlord_1011

    Warlord_1011 New Member

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    what size capacitor would you recomend?
     
  7. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Depends on the current required - but you get little from a 555 anyway.

    But this is why we asked for more details, you don't need AC to test lights anyway - DC is perfectly fine. Are you testing individual bulbs?, and are they 15V each?.
     
  8. dave miyares

    Dave New Member

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  9. Warlord_1011

    Warlord_1011 New Member

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    well im not so sure on the voltages of the bulbs, mainly because it had 2 wires, Live and Neutral and was wired straight to the plug, these lights are about 20 to 30 years old, and i wish to test individual bulbs, with a 9volt batery the fillement lights up but it does not light the bulb, i thoguht this was due to it being DC and not the AC the bulb usually uses
     
  10. Warlord_1011

    Warlord_1011 New Member

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    or would i have to use a circuit like this:

    DC to AC Inverter With the 555

    without the transformer converting it to 230v, i would only want 12 to 24VAC
     
  11. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    No, AC makes no difference - if it's only lighting slightly you've got too little voltage, or your source can't supply enough current (and a 555 certainly couldn't).

    Divide your mains voltage by the number of bulbs, that tells you what voltage they are - so 240V and 10 bulbs would be 24V bulbs.

    But you have no need to light the bulb brightly, if the filament glows with too low a voltage then it's fine.
     
  12. Warlord_1011

    Warlord_1011 New Member

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    oh ok, would a 555 timer, be able to control a transistor switch?, or would you not need it and wire the 555 up to do the same action?
     
  13. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Of course it can - but there's no reason to use a 555 at all - bulbs don't need AC. Like I said, count the bulbs.
     
  14. mbarazeen

    mbarazeen Member

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    if you have some other idea in mind to do with these bulbs, you better tell your idea. if what you need is only to test it and see wheather its ok or not, then what you get when you use 9V is enough to confirm it.
     
  15. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    If all you want to do is test individual lamps, they are usually 6V each, and they do not care if you feed them AC or DC. I just use my Ohmmeter :D
     
  16. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Old outdoors Christmas tree lights were 120V each (in Canada) and were all in parallel. For years I used clear ones as "night lights" because they were extremely inexpensive and in packages of many the day after Christmas.
     
  17. dougy83

    dougy83 Well-Known Member

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    15VAC has a peak-to-peak voltage of over 30V and a pulsating 15VDC has a peak-to-peak voltage of 15V; they are quite different, even with a capacitor.
     
    Last edited: Dec 20, 2009
  18. audioguru

    audioguru Well-Known Member Most Helpful Member

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    With a 15V supply, the output of a 555 is an 11V to 13V peak-to-peak square-wave.
    A 15V RMS sine-wave has a voltage of 15V or 42.4V peak-to-peak.
     
  19. Sceadwian

    Sceadwian Banned

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    Peak is irrelevant. RMS is more important.
     
  20. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    If you don't specify what you're measuring in, your post is completely meaningless.

    As long as you use the same measurements, and the same waveform, they are identical.
     
  21. dougy83

    dougy83 Well-Known Member

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    No idea what you're on about. 15VAC and pulsated 15VDC are completely different, both in amplitude, RMS, delivered power, etc. There are no 2 ways about it.
     
  22. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    15VAC p-p square wave is exactly the same as 15V p-p 'pulsed DC' - you can't just call something 15V AC with out specifying what it is.
     

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