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AC->DC converter without a diode.

Discussion in 'General Electronics Discussion' started by ratstar, Oct 10, 2020.

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  1. ratstar

    ratstar

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    Aug 20, 2018
    If you put ac into a capacitor, and the discharge of the capacitor is the output.

    Then the ac will charge it from neutral to positive, then youll get a back charge from the ac, and this will make it go back to neutral again. (so then you dont get a negative half cycle!)

    The problem is, if the capacitor is discharging, then this isnt true anymore, but you have to put a resistor on it anyway, to make the ac not take the discharge path and then this will start to make the capacitor act as a rectifier again.

    So a capacitor discharging into a resistor, might be able to rectify current too, without a diode.
     
  2. Nanren888

    Nanren888

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    Nov 8, 2015
    Not sure where the resistor you describe goes. Got a schematic.
    .
    Did you have a question?
     
  3. ratstar

    ratstar

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    Aug 20, 2018
    Heres a schem - It doesnt work yet. I think that maybe if supply power to the capacitor slightly in one direction - then it works maybe...

    [​IMG]
     
    Last edited: Oct 11, 2020
  4. Audioguru

    Audioguru

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    Sep 24, 2016
    With your very low resistor values and 60Hz then the capacitor must be a huge electrolytic one.
    When it gets the wrong polarity 60 times each second from the AC then it will explode.

    A series diode blocks the wrong polarity, it does not short it like your capacitor does.
     
  5. Nanren888

    Nanren888

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    Nov 8, 2015
    I'm sorry, but I have no idea what you are trying to do or ask.
    .
    Some capacitors such as electrolytics conduct, leak more in one direction, so will sort of rectify, but they are not designed for this and as suggested above will fail, quietly or loudly depending on charge, size, &c.
    .
    Remember that as the AC waveform heads downward after the voltage peak, it will also drain charge back from the capacitor if the capacitor voltage exceeds that of the AC..
    .
    If you replace the capacitor with a diode, to shunt the negative half cycle to ground, you will have a rather inefficient way of getting a positive half cycle only at the output. Might be a lot better to look into conventional circuits with series diode of diodes.
     
    bertus likes this.
  6. ratstar

    ratstar

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    Aug 20, 2018
    Thats not low resistance, it should even work with microohm resistors :)

    voltage dividers work with micro ohms.

    It could be any amount of power here, not just the wall socket.

    Its just an idea, I know that just using a diode is easier and works better- but I was wondering if there was a way to play around with resistors and capacitors and get the same effect.
     
    Last edited: Oct 11, 2020
  7. Nanren888

    Nanren888

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    Nov 8, 2015
    Nope.
    Not in any way that the capacitors have been designed to be used and therefore are likely to keep doing it for long.
     
  8. ratstar

    ratstar

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    Aug 20, 2018
    no probs then. ill just get back to my stuff, lots of work to do.
     
  9. ratstar

    ratstar

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    Aug 20, 2018
    Hang on, I think you dont need the capacitor, just add equal amounts dc to ac and then you get a rectified signal, no diode required.
     
  10. Nanren888

    Nanren888

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    Nov 8, 2015
    Yep, add 9 volts DC to 9 volts ac and you'll get entirely non-negative voltage, with an average DC level of 9 volts. Might be easier to just use the 9 volts DC.
    Sort of depends what you're trying to do, I guess. :)
     
    ratstar likes this.
  11. Audioguru

    Audioguru

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    Sep 24, 2016
    Of you add DC then the AC is not needed.
     
  12. bertus

    bertus Moderator

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    Nov 8, 2019
    Hello,

    This can happen when a capacitor gets the reversed voltage:



    Bertus
     
    Kabelsalat likes this.
  13. Audioguru

    Audioguru

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    Sep 24, 2016
    What a day!
    A few minutes ago I watched the Formula One car race and tried to translate the severe accents of the announcers from England and the severe accents of the drivers from all over the world.
    Now I watched this You Tube video from India with its severe accent.

    I suspect that the resistance of the breadboard, the wires and the alligator clips limited the current because with low resistance there will be enormous explosions.
    My first job was with a car radio manufacturer. On the production line there were a few backwards capacitor explosions each day.
    Luckily for the workers testing the radios, there were covers on the radios. In the lab, a capacitor explosion from an open radio caused bits and pieces of capacitor all over the place.
     
  14. ratstar

    ratstar

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    Aug 20, 2018
    Car stereos are amazing. Im a bit wierd tho, id like to make the whole thing from scratch, even the speaker! =)
    Not sure what it would sound like tho, but I bet it would be decent, avoiding the industry standard.
     
  15. Audioguru

    Audioguru

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    Sep 24, 2016
    Without learning about how radios work then your radio will not work.
    Without learning about how amplifiers work then your amplifier will not work.
    Without learning about how speakers work then you will ne lucky of yours sounds awful like a buzzer.

    The industry standard for car radios is excellent sound.
     
    Harald Kapp likes this.
  16. Nanren888

    Nanren888

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    Nov 8, 2015
    Look, I'd have to say "Go for it." You'll learn lots. Have a lot of fun. Probably in the end you'll, like many, have an even greater appreciation for the one you buy to use.
    On of the guys working here has been perfecting electrostatic speakers over years. His early ones sounded ok, but always looking to improve.
    The guy in the next office to me is an audio guy. He's been one of those trying switching amplifiers for years, now looking at using the chips you can so conveniently buy.
    From crystal sets to sophisticated ICs doing a lot of the radio for you, to software radios, everything has become much easier.
    .
    Take a look at what modules are available; making your own chips is tough, choose from components, chips, modules, ....
    .
    What he said was right, by the time you've finished, you'll know a lot about a lot of things.
     
  17. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Nope. AC (as in Alternating Current from a power source, such as a power line or the secondary of a transformer) ***always*** has a negative half-cycle. That's what the A in AC stands for.

    ak
     
    Harald Kapp likes this.
  18. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Ooooohhhh, a like from the boss. My day is all downhill from here.

    ak
     
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