Discharging effects

[audioguru]

....The....

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:

 

[walters]

timers and other oscillators are the only places where we're concerned with charging and discharging--


Sorry didn't know only timers and oscillators did only charging and discharging i'll have to read more about timers and oscillators in a charging and discharging point of view i never looked at them in this way
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[audioguru]

i'll have to read more about timers and oscillators in a charging and discharging point of view i never looked at them in this way

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

 

[DigiTan]

....The....

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.

 

[walters]

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?

 

[DigiTan]

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.

 

[walters]

Thanks guys

oscillators use the RC/RL decay

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?

 

[DigiTan]

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...

 

[audioguru]

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

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:

 

[walters]

Thanks guys for the help

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.

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?

 

[Nigel Goodwin]

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

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?.

 

[Styx]

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

: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

 

[walters]

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?

 

[walters]

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

 

[mstechca]

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

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?