On Oct 7, 5:00=A0pm, z <gzuck...@[EMAIL PROTECTED]
> wrote:
> On Sep 11, 1:44=A0pm, cabraha...@[EMAIL PROTECTED]
wrote:
>
>
>
>
>
> > On Sep 1, 12:41=A0pm, exxos...@[EMAIL PROTECTED]
wrote:
>
> > > Hi all,
>
> > > While messing with buck/boost circuits I had some thoughts which
don'=
t
> > > hold up in real tests....
>
> > > A simple example (aside from losses) is that if transfer energy from
> > > say 10V 10uF into 1uF the voltage will increase to preserve the
> > > charge.
>
> > > Now, in my circuit, I charge 25V 1,000uF capacitor and charge a 10uH
> > > inductor. When the switch turns off, all the energy should be in the
> > > 10uH inductance. So if I have a 100pF capacitor, then the voltage
> > > should be like 100,000volts according to my workings out.
>
> > > Now I ran a computer simulation on this, at best I can only obtain
> > > 12KV on the 100pF. So most of the energy is lost in switching losses
=
I
> > > assume.
>
> > > In realworld tests, I end up with =A0less voltage than I started out
> > > with, So I am trying to find out why ?
>
> > > I know charging 22uH inductor at 100khz can be used as a buck/boost
> > > supply, I built a simple 12V to 30V inverter, can switch 10amps
> > > easily. Though I am not running at 100khz, only 100hz. Though the
> > > current pulse rises to something like 500amps over 500uS.
>
> > > I am not sure I follow all this exactly, Or even if it will work ?
> > > AFAIK, The longer a inductor has current pumped across it the more
> > > charge it obtains over time. So at turn off, all the energy given to
=
a
> > > coil is recovered. It works well, even with my simple buck/boost
> > > circuit.
>
> > > So I am slightly confused as to why pu****ng 500A into a coil has no
> > > effect. I can only assume I have a huge loss somewhere, Or I do not
> > > follow the idea correctly ?
>
> > > Cheers,
> > > Chris
>
> > You need to aquaint yourself with the buck-boost topology and theory
> > of its operation. =A0If you go to TI's web site and download their
buck=
-
> > boost app note no. SLVA059, studying this thoroughly, you will
> > understand why.
>
> > In a nutshell, the 1000 uf input capacitor did not transfer ALL of its
> > energy to the inductor. =A0The output voltage is related to the input
> > voltage and the duty cycle as follows:
>
> > Vout =3D Vin * (D/(1-D)) not accounting for losses.
>
> > The energy transferred to the inductor is half the inductance times
> > the difference between the square of the final current and square of
> > the original current. =A0This is determined by the voltage across said
> > inductor multiplied by the on time. =A0During the power switch off
time=
,
> > the volt-seconds must equal that of the on time. =A0The app note
covers
> > this. =A0The value of the input capacitor does not determine the
output
> > voltage. =A0The same goes for the output cap value. =A0The values of
bo=
th
> > caps, however, are im****tant regarding ripple. noise, and transient
> > response.
>
> > Did I help? =A0BR.- Hide quoted text -
>
> > - Show quoted text -
>
> i haven't gotten the whole detail, but you seem to start with a bit of
> a misunderstanding which i will now endeavor to correct:
>
> you charge a capacitor by loading a voltage into it, then open
> circuiting it; but, an inductor being essentially the opposite, you
> charge it by loading a current into it and shortcircuiting it; whereas
> a charged capacitor holds its energy in the electric field with zero
> current, a charged inductor holds its energy in the magnetic field,
> with zero voltage. If you short circuit a capacitor it loses its
> charge, if you open circuit an inductor it loses its current. In real
> life, the series resistance in the inductor windings decays the
> charged current a lot more quickly than the leakage resistance in the
> capacitor decays the charged voltage.- Hide quoted text -
>
> - Show quoted text -
So where is my misunderstanding? What have you "corrected"? I know
the operation of inductors and capacitors. I looked over my previous
post and found nothing in need of correction. What specific point
have I made that you take issue with?
I've been developing buck-boost converters and SMPS for more than 2
decades, and have 2 published papers on SMPS in world wide peer
reviewed magazines. I've been a regular attendee at the Unitrode/TI
power seminars since the mid-1980's. I know my power supplies. I
referred you to a TI app note so that you can acquaint yourself with
the basics of buck-boost operation. Reading it is my advice to you.
Are you really looking for help. or someone to argue with? I offer
you free expert advice, and then I get a lecture on L and C basics?
Best regards.
Claude
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