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Discharging effects

Discussion in 'General Electronics Chat' started by walters, Nov 2, 2005.

  1. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Oops! Are you eating dinner or lunch now?
    I hope you aren't a big (fat?) guy who eats more than twice as much as most people.
    Waiting for your continuation (burp!) :lol:
     
  2. walters

    walters Banned

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    [/code]
     
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Never mind looking at charging and discharging in timers. I thought you were looking at guitar amp circuits.
     
  4. dave

    Dave New Member

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  5. DigiTan

    DigiTan New Member

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    I think someone really heavy stepped on my net cable when I sent that one. :lol: But seriously, I was going to say something to the effect of: The discharge pin works like you described.
     
  6. walters

    walters Banned

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    I was trying to look at guitar amp circuits in a discharging and charging point of view the discharging paths ways but i guess its not the right way or no theory behind it

    For oscillators and timers whats the theory behind discharging and charging curves and discharging times?

    Is the Time period for a oscillators and timers the same for the discharge and charge time just multipled X 5 times?

    Why do oscillators and timers uses discharging and charging time periods?
     
  7. DigiTan

    DigiTan New Member

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    Yeah, with something like an amp, you have to look as the capacitor's AC-passing (impedance) abilities instead.

    The theory for oscillators is generally the same as we discussed on RC and RL circuits. Timing is done by repeatedly chargine & discharging the capacitor and triggering the output when the capacitor voltage reaches some arbitrary point. The same could be said for inductors, except they have an ability to interfere with each other magnetically, so they are less common. In short, it's all about exponential decay.

    The time period for an oscillator is whatever you design it to be. I imagine the 555 timer used the 33% and 66% voltages for easy calculations.

    In fairness, not all oscillators use the RC/RL decay. They're just highly popular because of thier low cost, wide availability, and small space; versus crystal oscillators which are higher cost, lower availability, and higher accuracy. You can also mix-and match R's and C's or use variable ones to "tweak" it to frequencies you can't easily get with fixed crystals. It's a matter of trade-offs.
     
  8. walters

    walters Banned

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    Thanks guys

    How does the RC decay wouldn't i need comparators or a discharing transitor to shut the voltage off and on to make the RC network decay ?

    I thought oscillators was just positive or negative feedback loop where is the RC decay or RL decay being turned off and on to get a decay at? or discharing and charging?
     
  9. DigiTan

    DigiTan New Member

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    That's also correct, some oscillator types like Wein Bridge (Op-amp) for example, use a negative feedback loop. I think the type that uses the charge/discharge behavior is the push-pull oscillator, and maybe one of the others forum guys can confirm or correct me on that one...
     
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The 555 timer has a comparator to sense when the voltage of its timing capacitor has reached 67% of the supply voltage, another comparator to sense when its timing capacitor has discharged to 33% of the supply voltage and a transistor is used to discharge the timing capacitor sometimes through a resistor.

    All oscillators use positive feedback. The RC networks in a Wien bridge oscillator cause loss, so its loop gain must be slightly more than 3 in order to oscillate. An unbuffered phase-shift oscillator has a loss of ..... hello? :lol:
     
  11. walters

    walters Banned

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    Thanks guys for the help

    So the comparators are used to keep the charging times and discharging times to a "percentage voltage range" 67% and 33%?

    What are the charging and discharging times used for to create square waves? or a duty cycle ? or a time period?
     
  12. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    You seem to have a fetish about charging and discharging?, it's not helping you at all! - it's a subject you might be taught in an odd 10 minutes on a quiet afternoon, as part of a four year course.

    It's really THAT unimportant!.

    Things you NEED to know!.

    1) T=CxR - T in seconds, C in farads, R in ohms.

    2) Capacitors NEVER charge fully, it's an exponential charging curve, so can't ever reach 100%.

    3) 5xCxR is considered 'close enough' to fully charged.

    That's really about all there is you need? - perhaps I exaggerated about 10 minutes?.
     
  13. Styx

    Styx Active Member

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    :roll:
    The charging/discharing of a capacitor is exponetial-shaped.
    It takes extra circuitry to make a squarewave.

    The simplest is a comparator.
    In using a comparator a squarewave cap be produced.
    The period is set by the time-constant of the RC
    The duty-cycle is set by the hysteresis of the compartor


    its not as simple as that since chanigng hysteresis will effect the period as well but that is more to do with implimentation
     
  14. walters

    walters Banned

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    Thanks for the information

    So why does a 555 timer use the timing cap. for discharge and charge times when it needs comparators and other circuit to make a square wave?

    Can't the comparators just have or use Fixed voltages insteand of charging and discharing a capacitor?
     
  15. walters

    walters Banned

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    Circuit for Time-Constant Measurement:

    1.) use a Square Wave source "this is the key"

    Each time the square wave input voltage goes UP or high
    the "inductor" or "capacitor" is energized
    When the square wave goes back to zero the "inductor" or "capacitor" is discharging, the exponential resistor voltage its value equals "5" time constants


    The Discharge Time constant Formula is RC=T

    (10K)(2uf)= 20ms X 5 = 100ms
     
  16. mstechca

    mstechca New Member

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    Why do you care?
    7 pages.... this is ridiculous. It even took me 10 minutes to read posts since my last one.

    anyways, you need to know these points:

    #1. a capacitor is 100% necessary for any timing circuit to operate. Why? because a capacitor is able to store charges.

    #2. A resistor MUST come with a capacitor in a circuit to create the proper timing.

    #3. The shape of the waveform CANNOT vary with time, but the number of waves CAN. For example, You can't make a time constant of 1 second equal to a square wave, and you can't make a time constant of 2 seconds equal to a triangle wave, and you can't make a time constant of 3 seconds equal to a sine wave.

    The height of a wave is dependant on voltage.

    is there any other practical thing you need to know?
     

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