# Re: Mot DC Ps

```Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Mddeming-at-aol-dot-com>

In a message dated 2/17/01 11:42:58 PM Eastern Standard Time,
tesla-at-pupman-dot-com writes:

>
> Original poster: "Luc by way of Terry Fritz <twftesla-at-uswest-dot-net>" <
> ludev-at-videotron.ca>
>
> Tx Matt
>
> You lost me after the first paragraph but R=2*sqrt(L/C) is simple if I
> don't have
> any real inductance except for parasitic could I use something like 10ˆ-6 H
> for
> value of L in the equation.
>
> Luc Benard
>
>
> > >
> > > I have a question too when you discharge a cap though a resistance for a
> > > certain value of R you have an oscillating circuit (because of parasitic
> > > inductance ), if you increase the value of R to a certain point the cap
> > > will just discharge whit out oscillation how do you calculate this
> > > value.
> > >
> > > Tx
> > > Luc Benard
> >
> > Hi Luc
> >         The critical point is at R=2*sqrt(L/C). If R is greater than this
> > value, no oscillation takes place. The frequency equation
> f=1/((2pi*sqrt(LC)
> > is actually a simplifications of:
> > F=sqrt(1/LC-(R/2L)^2)/2pi

If the frequency F of the oscillations is known for a given value of R, the
effective parasitic L can be calculated from the equation
F=sqrt(1/LC-(R/2L)^2)/2pi and then the critical value of R found from
R=2*sqrt(L/C). In the absence of a way to measure F, yes, you can
"guesstimate" L and try the resulting values of R until oscillation stops.

Matt D.

```