[Re: 7820 regulator source...?]

[Harry Bissell]

Harry Bissell writes: Another good way is to use a 5.1 volt zener diode in
series with the ground lead. Very independant of device quiescent current and
well regulated. Or for cheap, use diodes (forward biased for .7 volts per
diode. I use this trick to boost a 5volt regulator to 5.7 volts, then put a
diode in series with the output to give 5 volts again. Why??? for computer
apps with battery backed up memory. Then you can run the memory chips diode
isolated from the 5 volt supply, without the usual problems of the memory
running at 4.3 volts. This is a shitty way to interface memory. It was done on
my Oberheim Matrix 6 (which would screw up the memory every once in a
while...) I also used this trick to make a six volt car (lighter plug) adapter
for a portable radio.   :-) Harry Bissell


Gene Zumchak <zumchak at cerg.com> wrote:
Rob,

    Quiescent current for a 78XX is about 3 ma.  If you connect about a 1.6K
resitor from a 7815 ground pin to ground, you'll drop about 5 volts across the
resistor and the regulator will ride on a five volt pedestal.  Bypassing the
resistor won't hurt.  If you were doing this for a lot of systems, you would
use a smaller resistor and connect another resistor from the output to the
ground lead.  This provides 15/R of current.  If this is few times larger than
3mA, then the output will be less dependent on the quiescent current.

Gene Z.



Rob Hukin wrote:

> Anyone know of a source for these 20V regulators? Slightly off topic
> (apologies) but it's for an old Revox B77 and good old Revox want to charge
> me 15ukp for one!
>
> rob.


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