Re: -5V on IIgs

["bieling@terra.es" <bieling@terra.es>]

On Mar 4, 11:27 pm, Don Bruder <dak...@sonic.net> wrote:
> The 7905 (a negative 5 volt regulator - normally supplied with negative
> 7-20 volts on the input pin, and putting out a regulated negative 5
> volts on the output pin) gets wired into the positive 12 volt supply
> such that it thinks it's seeing -12 volts, by simply wiring the input
> pin of the regulator to ground, and the ground pin of the regulator to
> +12 volts. It's wired "backwards" as far as usual practice is concerned,
> but to the regulator, it's running on a -12 volt input source. The
> output pin spits out a regulated -5 volts. Which is precisely what he
> needs - negative 5 volts.

Think of it this way: the 7905's output pin is going to be at 5v less
(-5v) than it's ground pin...
but,
It's ground pin is connected to +12v, not to ground...
therefore,
It "spits out" 5v less than +12v = +7v, referenced to ground.

In other words, -5v referenced to +12v
is not the same as -5v referenced to ground.

Jorge.