Russell McMahon wrote:
>
> > I am putting 24volts in to a 7905 to get a -5volts out.  The 7905 does get
> > warm with a large heat sink...no it gets hot.  Is there something like the
> > Black regulator that I could use to cool things down?  Keeping ripple to a
> > minimum is very important, thats why I used a linear regulator.  I've
> always
> > had a difficult time reducing ripple.  Any help is appreciated.
>
> You could use something EXACTLY lime the Black Regulator as a pre-regulator
> provided it meets your power requirements.
>
> For a negative input and output voltage you need to "invert" every active
> component.
> Replace any NPN with a PNP, and PNP with an NPN, reverse the "direction of
> all diodes and zeners, feed input negative below ground and expect negative
> output below ground (ground connection stays the same in old and new
> versions)  and voila - a negative input & output black regulator. Using this
> to feed you existing 7905 with about 8 volts will allow it to operate at
> much lower temperature while still providing the good regulation of a linear
> regulator.
>
> As you are dissipating highish power now you are probably working at the
> better part of 1 amp load. If so you will need to design the black
> pre-regulator accordingly. Suitable output transistor and an inductor that
> doesn't saturate at the required current levels are probably the main
> requirements.
>
> Roman may be prepared to suggest component values to get you started.


Sure, given the data for max load current and
expected input voltage range. :o)
-Roman

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu