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'[EE]: Dual Voltage help'
2002\05\29@130110 by Tal Bejerano - AMC

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part 1 309 bytes content-type:text/plain; (decoded 7bit)

Hi 2 All

Look at the attached files, it's a schemes from 2 sites , look at the
capacitors mounted on the negative rail.
which one is correct or I miss something here? in which order should be the
capacitors on the negative rail?

Regards

Tal Bejerano
AMC - ISRAEL
>




part 2 1175 bytes content-type:Image/GIF; (decode)

part 3 4039 bytes content-type:image/gif; (decode)


part 4 131 bytes
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2002\05\29@131812 by shawnmulligan

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The potential of the ground rail (0V) is greater than the potential of the
negative  rail (-15V), so the caps are correct, with the positive side going
to the higher potential (0V).

> Hi 2 All
>
> Look at the attached files, it's a schemes from 2 sites , look at the
> capacitors mounted on the negative rail.
> which one is correct or I miss something here? in which order should be
the
> capacitors on the negative rail?
>

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2002\05\29@135059 by M. Adam Davis

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They are both correct.  What you are missing is the idea that the + side
of an electrolytic cap must always be at a higher potential than the -
side of the cap.

In both circuits this is the case.  The second circuit shows the +
connected to gound and the - connected to the negative 15 volt supply,
which is at a lower potential with respect to ground.

-Adam

Tal Bejerano - AMC wrote:

{Quote hidden}

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2002\05\29@135923 by Mark J. Dulcey

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Tal Bejerano - AMC wrote:
> Hi 2 All
>
> Look at the attached files, it's a schemes from 2 sites , look at the
> capacitors mounted on the negative rail.
> which one is correct or I miss something here? in which order should be the
> capacitors on the negative rail?

The capacitors are oriented correctly in both drawings. The positive end
of a polarized capacitor always goes toward the circuit point where the
voltage is more positive.

In your first drawing, ground is shown in the middle. V+ (drawn above
ground) is more positive than ground. V- is more negative than ground.
So the cap going from V+ to ground has the + end at V+, and the cap
going from ground to V- has the + end at ground. This voltage divider
will only work well when the current demand is low (the rule of thumb
about circuit impedance says that the input impedance of the load should
be at least 10K - 10 * the 1K resistors in the divider - which would
limit the current to about 1mA), though it will also behave if the
current drains from the V+ and V- terminals are equal or nearly so
(again giving you a divider with equal resistances on each leg).

In your second drawing, the grounds are shown near the regulator
components. The in and out terminals of a 7815 (fixed voltage positive
regulator) are more positive than ground, so those caps have the + ends
on the in and out terminals. The in and out terminals of a 7915 (fixed
voltage negative regulator) are less positive than ground, so the + ends
of the caps go to ground. This circuit can supply more current (1A each
from V+ and V-, though I might use larger diodes than 1N4001s if I were
going to approach that limit), and will remain well-regulated even if
the positive and negative current draws are unequal.

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2002\05\29@164832 by uter van ooijen & floortje hanneman

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> Look at the attached files, it's a schemes from 2 sites , look at the
> capacitors mounted on the negative rail.
> which one is correct or I miss something here? in which order should be
the
> capacitors on the negative rail?

All are correct, which would probably be easier for you to see if you
mirrored the 7915 circuit around the x-axis (so the ground ends up above the
negative rail, as in your first circuit).

Wouter van Ooijen
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2002\05\29@171132 by Olin Lathrop

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> Look at the attached files, it's a schemes from 2 sites , look at the
> capacitors mounted on the negative rail.
> which one is correct or I miss something here? in which order should be
the
> capacitors on the negative rail?

All capcitors in both drawings seem to be shown correctly.  The + side is
always toward the more positive voltage.  Everything seems right.  What
specifically is the problem?


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