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
>
>
> Vasile Surducan wrote:
> >
> > The easyest way is to built a two coil inductance ( terminals
> > a,b,c). Supply the coil at terminal "b" with 1,5 or 3V. At terminal
> > "a" one FET or mos-FET transistor with small r-DS and V-GS, connected with
> > drain. Source to ground , gate to a simple oscillator ( could be a
> > positive feedback self oscillator, but then instead of a simple inductance
> > will be a transformer ). At terminal "c" you'll have a magnified
> > oscillation voltage. Rectifying with fast swiching diodes and filtering
> > will gave you 5V. Negative stabilisation feedback is not necessary for
> > small loads.
> > Computing the wrapping wire numbers using Faraday's law.
> >
> > Cheers, Vasile
> >
> > On Tue, 11 Sep 2001, Octavio P Nogueira wrote:
> >
> > > What about the opposite?
> > > >From 1.5V or 3V to 5V?
> > > I know there are several IC doing that
> > > but here in Brazil it's not that easy to get them.
> > >
> > > Friendly Regards
> > >
> > > Octavio Nogueira
> > > ===================================================
> > > nogueira@propic2.com                  ICQ# 19841898
> > > ProPic tools - low cost PIC programmer and emulator
> > > http://www.propic2.com
> > > ===================================================
> > >
> >
> > --
> > http://www.piclist.com#nomail Going offline? Don't AutoReply us!
> > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body
>
> --
> http://www.piclist.com#nomail Going offline? Don't AutoReply us!
> email listserv@mitvma.mit.edu with SET PICList DIGEST in the body
>
>

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body