Yes, you have right, I had thought to large current.
Thanks also to Octavio which is thinking to the piclist people.
Vasile


On Thu, 13 Sep 2001, Roman Black wrote:

> Hi Vasile, small Vce is possible with cheap
> bipolar transistors, at low currents anyway.
> The main use for this would be to use a D cell
> or C cell (etc) battery to power your PIC
> product, instead of a 9v battery. So the
> 5v output current needed would only be low,
> for most of my projects 5mA to 20mA is plenty.
> -Roman
>
>
> Vasile Surducan wrote:
> >
> > Roman, a cheap step-up with ordinary transistors from 1.1 V is a real
> > challenge ! You need very small VCE if you think to bipolar transistors,
> > but I think bipolars can't be used here.
> > Even serious circuits like LT 1930 ( 1Amp ) running at 1...2MHz have a
> > minimum 2.6V input voltage.
> > About efficiency, I think 60% will be pretty good.
> > But I preffer to design a little expensive circuit than to have problems
> > with sorting transistors for high-est gain.
> > Vasile
> >
> > On Wed, 12 Sep 2001, Roman Black wrote:
> >
> > > Hi Vasile, how about a challenge, for a simple
> > > step-up circuit to power a 4v to 5v PIC from
> > > a 1.5v battery, or even a 1.2v NiCd cell.
> > >
> > > I know chips are available to do this, but
> > > with price and availability problems.
> > > A cheap 2-transistor circuit that does this
> > > (and regulates ok) would be very useful.
> > >
> > > So, who can suggest a super cheap circuit that
> > > does this:
> > > * 2 or 3 cheap transistors
> > > * ONE standard pre-wound cheap inductor
> > > * ok for 1.1v input (discharged NiCd cell)
> > > * 4v or 5v output, reasonable regulated
> > > * cheap total parts cost and small size
> > > * decent efficiency
> > >
> > > Maybe a simple boost or buck-boost circuit?
> > > Similar to the high-gain self oscillating things
> > > that Russell and myself have been playing with?
> > > :o)
> > > -Roman
>
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