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PICList Thread
'It's wrong. 5Vdc supply'
1998\10\14@223319 by Eduardo Rivera

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It took me some time trying to figured out how is possible to get 5 volts
D.C. from this circuit and  finally decided to ask for your opinion.
It was hard  for me to belive the drawing is wrong because this circuit was
found on the Internet and it's the power supply for a PIC application.

Can't we trust on applications downloaded on line? Even from well known
sources.

-------------
EDUARDO WROTE:

> Hi all guys,
>Could someone give me his thoughts about this circuit?(hope is clear ASCII).
>It is supposed to supply 5 volts and is powered directly from AC, 220 Volts
>in this particular case. It looks for me that the zener is wrongly biased.

0  <-------------- 220 Vac ---------------->      0
|                                                 |
|                                                 |
x----------|(-----\/\/\/\/----x-------|<|---------x Gnd
        220nF     1K 5W      |                   |
                             |                   |
                             |            100nF  |
                             x--|>Z----x---|(----x
                                       |         |
                        5 V  zener     |         |
                                       0         T Gnd
-----------------------------               5Vdc
Peter wrote:
>>The zener is wrongly biased, swap the diode and the zener around. Also add
>>a 470K 0.5W resistor in parallel with the 220nF.

>>Peter
-------------------------------
{Quote hidden}

1998\10\15@124725 by Peter L. Peres

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On Wed, 14 Oct 1998, Eduardo Rivera wrote:

>  It was hard  for me to belive the drawing is wrong because this circuit was
> found on the Internet and it's the power supply for a PIC application.
>
>  Can't we trust on applications downloaded on line? Even from well known
> sources.

You can't trust:

a) People you know
b) Parts and assemblies bought without a certificate from a reputable
source, even if others use them by the zillions
c) Most drawings and diagrams and tables in reputable books that have no
published errata
d) Your own engineering calculations (if you don't check yourself you're a
fool imho)
e) Your most trusted instruments (do you short the DVM cables between them
every time before testing ohms ? I do ;)

In any case, use extreme caution when building something after a net
document. This includes asking questions before you build.

Peter

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