Digest Number 163
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> t 08:21 AM 7/25/00 -0500, Mike DeMetz wrote:
> > The power dissipated is a function of the voltage AND current. A
> > 78xx
> >series regulator needs about 2.5V overhead. If you are running 12V in
> >you have to drop 4.5V(12-5-2.5). 4.5x.2=.9W .
>
> Sorry, Mike, but the above is not correct. The dropout voltage only
> reflects how much higher the input voltage must be than the output for
> correct operation. The dissipation is calculated by the total voltage
> across the regulator X the current. In other words, your figures
> above should be (12 - 5) X .2 = 1.4 Watts.
>
> dwayne
>
Yes, as I thought about it after I posted I realized that the overhead
was part of the dropped voltage.
> > The power dissipated is a function of the voltage AND current. A
> > 78xx
> >series regulator needs about 2.5V overhead. If you are running 12V in
> >you have to drop 4.5V(12-5-2.5). 4.5x.2=.9W .
>
> Sorry, Mike, but the above is not correct. The dropout voltage only
> reflects how much higher the input voltage must be than the output for
> correct operation. The dissipation is calculated by the total voltage
> across the regulator X the current. In other words, your figures
> above should be (12 - 5) X .2 = 1.4 Watts.
>
> dwayne
>
Yes, as I thought about it after I posted I realized that the overhead
was part of the dropped voltage.