I really don't understood why you need an IC doubler when you can do it
with or without using one pic pin. If you try to double the negative
output of the max 232 you'll have some problems, first one is that voltage
is already doubled and have a small output current capability.
Try it with a simple doubler bridge ( but disconnect any capacitor from
the max232 negative pin to ground before )
Better is Dimitry's solution, or one pic pin as oscilator ( 1 to 10kHz is
ok ) a npn buffer with a small resistor in colector ( 100...200 ohm) to
+5V and a network tripler ( 3 diodes and 3 47...100 micro capacitors )
connected for your desired polarity.

Cheers, Vasile

On Sun, 12 Aug 2001, Robert E. Griffith wrote:

> Hello,
>=20
> Does anyone know of a simple, cheap DC-DC negative voltage doubler that c=
an
> double the =968.5 of a MAX232 to at least =9612v at 2ma?
>=20
> Or, do you know of an inverting voltage tripler that would take a +5v
> to =9615v (less the V drop across the tripler)?
>=20
>=20
>=20
> Details=85
>=20
> I got some help on this topic a couple of weeks ago that pointed me in th=
e
> right direction. After researching it on and off for these weeks I have
> learned a lot and have several solutions, but I thought I would pursue th=
is
> one last way before settling on one.
>=20
> I am creating PIC base LCD circuit that has a +5v regulated supply coming
> in.  The LCD needs a =968v to =9612v bias at less than 2ma. The optimum v=
alue
> varies from LCD to LCD so it needs to be set with a pot. Since the curren=
t
> requirement is so low I can use a simple resistor and pot passive voltage
> divider to adjust the voltage down, if I can just get a voltage equal or
> less (more) than=9612v.
>=20
> I can get =968.5v from the unused half of a MAX232 on the board.  Too bad=
 the
> MAX232 does not drive the output to RS232=92s full +-12v spec!
>=20
> So it seems that all I have to do it double that =968.5v from the MAX232
> to =9617v (less the V drop across the doubler) and then drop it down with=
 a
> passive voltage divider.
>=20
> What is a simple way to double a negative voltage?
>=20
> I am assuming that since I only have DC to start with that I cannot build=
 a
> simple discrete solution.
>=20
> The only negative voltage doubler I have found is the LT1045 and it is a
> little more expensive than I would like (about twice the cost of other DC=
-DC
> Ics I have looked at like the LTC1044) and it requires a lot of external
> components when acting as a negative doubler.
>=20
> Does anyone know of a simple, inexpensive (<$2 in quantity 100) IC? I hav=
e
> mainly looked into IC DC-DC inverters/doublers from Maxim, National, Toko
> and TI.
>=20
> Thanks,
>=20
> --BobG
>=20
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.
>=20
>=20

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