Tjaart van der Walt wrote:
>
> Mitch Robbins wrote:
>
> > I'm looking at the potential of using a pic output, possibly PWM, to drive a
> > charge pump/switched capacitor circuit for generation of negative voltages.
> > I need approx 10mA at -15v.  I'm trying to avoid that extra chip or 2.   A
> > home brew 7660?
> >
> > I'm sure someone has been there before.  Has anyone had any luck in this
> > area, have circuit concepts, good references, or theory.
>
> You won't be able to do it directly if you want 10mA @ -15V. Assumingyou have
 perfect voltage
> translation (which won't happen), you will have to
> draw at least 30mA from a pin. This falls into the 'kaboom' section of the
 absolute
> maximum specs.

If you have three pins to spare how about a ladder

pin3--Cap---@--->I----------@---------- 15V
            !               !
            !---I<--!      Cap
                    !       !
pin2--Cap---@--->I--@-------@
            !               !
            !---I<--!      Cap
                    !       !
pin1------->I-------@-------@
                            !
                           Cap
                            !
ground----------------------@-------

5 caps and 5 diodes


Peter Cousens
email: peter@cousens.her.forthnet.gr  phone: + 3081 324450, 380534
snailmail:  Folia, Agia Fotini, Karteros, Heraklion  Crete, Greece.