At 08:57 AM 10/6/2009, you wrote:
>Michael Rigby-Jones wrote:
> > Are you genuinely failing to understand what people are trying to
> > explain, or are you now trolling?
> >
> > 1) With a 5v signal, and a potential divider of 2k and 3k, the final
> > voltage will be 5 * 3/(2+3) = 3v.  The source impedance will be 3k||2k =
> > 1.2k.  The 10%-90% voltages will be 0.3v-2.7v.
> >
> > 2) With a 5v signal, and a potential divider of 2k and 2.95k, the final
> > voltage will be 5 * 2.95/(2+2.95) = 2.98v.  The source impedance will be
> > 2.95k||2k = 1.19k.  The 10%-90% voltages will be 0.298v-2.682v
> >
> > Assuming both circuits are driving the same capacitive load the rise and
> > fall times will be slightly lower (faster) in the second case due to the
> > lower source impedance, but the voltage swing will be slightly lower as
> > well.  Do you now understand?  If not then I can recommend 'The Art of
> > Electronics' to gain a basic understanding of these principals.
>
>First, we are talking only about rising voltage on a capacitor, we ARE
>NOT talking about how the capacitor will be DISCHARGED through the
>resistors, please, re-read my previous post.
>
>Second, let's refresh the scheme: we have a capacitor connected to
>ground by one leg and through its other leg and resistor R1 getting
>connected to DC source. Also there is a resistor R2 connected to the
>capacitor IN PARALLEL. That second resistor _ALWAYS DISCHARGES the
>capacitor, that is, tries to diminish the voltage on the capacitor,
>you may call that resistor - leakage resistance.
>
>How, the hell on the earth, lower R2 value, that is increase in
>current leakage to ground from the capacitor would help the DC source
>to charge the capacitor faster through the same constant resistor R1?
>Lower R2 would mean lower impedance according to you.

I also would recommend _Art of Electronics_ -- it is aimed at those who
wish to get a quick grasp of electronics without delving too deeply into
theory and math (originally created for physics grad students who needed
to be able to quickly create useful scientific apparatus, AFAIUI). Of
course *some* math is required, but I don't think it goes much beyond
1st year Uni.

The current (2nd) edition is getting a bit long in the tooth (1989), but still
quite useful. Last I talked to Win, he was hard at work on the 3rd edition
which should be out Real Soon Now (it has been assigned an ISBN at least/
at last: 0521809266). When it is released, the prices of used 2nd editions
should drop.

Best regards,










>--
>http://www.piclist.com PIC/SX FAQ & list archive
>View/change your membership options at
>http://mailman.mit.edu/mailman/listinfo/piclist

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist