--- In "Adam Liberman" <> wrote:
>
> Hi,
>
> --- In "Rich Peet" <richpeet@> wrote:
> > DC-DC converter in the normal primitive sense is a Voltage Regulation
> > IC. A common one is the LC7805 which is a 5 volt regulator.
> ...
> > In recent years some manufacturers are getting smart and using this as
> > an advertising plus. The SD722 recorder markets their recorder as
> > being able to accept 10 to 18 volts. They likely are using a LC7805
> > and allowed a 2X safty for voltage spikes and the like.
>
> This is incorrect. A xx7805 is a IC linear regulator. A DC-DC
> converter is completely different -- it is a switching regulator, and
> contains various ICs and transistors as well as capacitors and
> inductors. Sometimes all this is contained within a sealed module. A
> linear regulator works by dropping the excess voltage as heat, so it
> is wasted. A switching regulator turns on and off very rapidly
> (usually 40KHz and up) to regulate the voltage, so it can be very
> efficient (up to 93% or so), and wastes very little power as heat. The
> trick in designing audio devices is to prevent any of the switching
> noise from becoming audible.
I understand but didn't want to go there. This is why I used the term
"primitive". I have not put a variable supply on a SD722 yet to
figure out how battery wise the design is. I will get around to that
and report if I find anything interesting that is not in the manual.
>
> Virtually all portable battery operated devices use switching
> regulators in order to conserve battery life and reduce heat, and do
> not use linear regulators like the 7805. When the SD722 says 10 - 18
> volts, that is an absolute range. The switcher likely can not reduce
> its duty cycle any further to regulate a higher voltage. In addition,
> a higher voltage may exceed the maximum voltage and power ratings of
> the semiconductors, inductors, and capacitors in the circuit and
> damage the recorder. Some devices, like some cassette and minidisc
> recorders, also use the unregulated battery voltage to power some
> circuits, and exceeding the specified voltage range may destroy these
> components.
>
> On portable recorders that only specify one input voltage, like 6
> Volts, it is likely they can tolerate a little more, like 6.4 (fresh
> batteries) or 7.5 (unloaded unregulated power adapter). But without
> analyzing the schematic for voltage and power ratings, and testing the
> internal heat dissipation at various voltage levels and ambient
> temperatures (which no-one is likely to go to the trouble to do), or
> having input voltage specifications from the manufacturer, you should
> keep the input voltage very close to the specified figure.
>
> Thanks,
> Adam
>
Since a variable voltage regulator is so easy to builld if one wants
to make sure to keep voltages in line then consider building a small
box around the LM317. Linked is a small regulator I built and the trim
pot for changing the output voltage is screwed under the cover.
Circuit diagram is on the card at radio shack where you can buy the part.
http://home.comcast.net/~richpeet/LM317T.JPG
I would show the inside but I just wired it "dead bug" then filled the
inside of the box with epoxy. This makes it easy, waterproof, and
shockproof.
Rich Peet
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