## Re: [Technical_Insanity] 9 volts from 12 volts?

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• Using one inline resistor works if the current requirment is always constant. If not then a voltage divider is not practical if you intend to get any type of
Message 1 of 10 , Sep 30, 2006
Using one inline resistor works if the current requirment is always
constant.

If not then a voltage divider is not practical if you intend to get any type
of voltage regulation.
To get good regulation in a divider, the current through the dropping
resistor has to be large compared to the curernt used by the device (meaning
the imput resistance of the device has to be much larger than the dropping
resistor. Dividers are almost never practical in real life for anything
that requires any kind of current.

The diode idea works for any current level (within the power constraints of
the diode that is). If the device uses 20ma then power lost in the diode is
very low.

Grim

----- Original Message -----
From: "Dean" <dean@...>
To: <Technical_Insanity@yahoogroups.com>
Sent: Saturday, September 30, 2006 10:27 AM
Subject: Re: [Technical_Insanity] 9 volts from 12 volts?

> Don't forget to figure out just how much current it will need and
> provide a GREAT heat sink to dissipate the drop. Personally,
> I'd just calculate the current/voltage drop and use resistors to drop it
> to the necessary requirements. At that point, I might also
> add the 7809, just to be sure, but there is often enough variance on the
> equipment (+/- 10% ) to accomodate the resistor method alone.
>
> Mark Mraz wrote:
>
>> Well, you could get a voltage regulator who's name is some variation of
>> a 7809 (9 being the target voltage). I have never used one of these,
>> but I have used a 7805. I assume they are basically the same. It's a
>> 3-pin device. Two are input voltage and ground. The third is the
>> output voltage, 9V in your case. There are also typically a couple of
>> capacitors involved, one between the input and ground, and one between
>> the output and ground. That's pretty much all there is to it.
>>
>> Mark
>> http://www.MarksHauntedGarage.com/halloween
>> <http://www.MarksHauntedGarage.com/halloween>
>> Live in or near western NY? Join the western New York email list.
>> See http://wny-haunters.MarksHauntedGarage.com
>> <http://wny-haunters.MarksHauntedGarage.com> for details.
>>
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• I have used 7809 that I purchased from Mouser electronics to solve a similar problem, I was running a 9VDC wall wart that turned out to be unregulated and it
Message 2 of 10 , Oct 2, 2006
I have used 7809 that I purchased from Mouser electronics to solve a
similar problem, I was running a 9VDC wall wart that turned out to be
unregulated and it was driving the chips on my board crazy.

--- In Technical_Insanity@yahoogroups.com, Mark Mraz <mark@...> wrote:
>
> Well, you could get a voltage regulator who's name is some
variation of
> a 7809 (9 being the target voltage). I have never used one of
these,
> but I have used a 7805. I assume they are basically the same.
It's a
> 3-pin device. Two are input voltage and ground. The third is the
> output voltage, 9V in your case. There are also typically a couple
of
> capacitors involved, one between the input and ground, and one
between
> the output and ground. That's pretty much all there is to it.
>
> Mark
> http://www.MarksHauntedGarage.com/halloween
> Live in or near western NY? Join the western New York email list.
> See http://wny-haunters.MarksHauntedGarage.com for details.
>
>
> denskirk wrote:
> > I'm not knowledgeable in circuitry design but can follow
directions. Can I build a circuit that I can use a 12Vdc power
source and get 9 volts to operate one of the RS 20 second sound
players? This will eliminate a 9Vdc wall wart that has already
replaced a 9V battery. Maybe the player can handle the 12 volts???
The paperwork with it just says 9V.
> >
> > Thanks
> >
> > Daniel
> > www.darkspectre.com
> >
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