[R-390] OT: Ramp Generators

[Barry]

Hi Roy,

Ahh, okay.  That's a small detail I missed.  Indeed, the sample I was looking at states it's a steady current (through a transistor).  That makes sense to me now.

Thanks for the explanation.  My electronics world is back in order now.

Barry - N4BUQ

----- Original Message -----
> From: "Roy Morgan" <k1lky68 at gmail.com>
> To: "Barry" <n4buq at knology.net>, r-390 at mailman.qth.net
> Sent: Friday, April 26, 2019 10:55:16 AM
> Subject: Re: [R-390] OT: Ramp Generators
> 
> Barry,
> 
> Some bits in reply - hopefully useful:
> 
> The usual capacitor charging curve shown in texts and explanations assumes
> (usually states) that the charging current comes through a fixed resistor
> from a steady voltage source. We see the familiar exponential curve
> approaching the source voltage as time goes on.
> 
> BUT in ramp generators there is usually a constant CURRENT source. This
> produces a linear voltage change with time on the cap.
> 
> Tektronix produced a number of explanatory documents related to their
> oscilloscopes, and I am sure one of them tells about time bases. I can send
> more info on that later but in the meantime search for “tekwiki”:
> W140.com/tekwiki/wiki ... main page, scroll way down to find “Concept
> Series”.
> 
> The Tektronix folks were/are masters at ramp generators.
> 
> Roy sends.
> 
> > On Apr 26, 2019, at 11:01 AM, Barry <n4buq at knology.net> wrote:
> > 
> > Hopefully this isn't too dumb of a question, but I was wondering how ramp
> > (sawtooth) generators work ...
> > 
> > This is confusing to me.  Capacitors don't charge linearly, do they, and,
> > if that's true, then why is the ramp linear wrt time?
>