On Mon, 22 May 2006 17:02:56 GMT, bigdaddy
wrote:

Hi all

I am learning electronics and for my bread board I have build myself a
voltage regulator to get 9V using the following circuit :

http://www.velleman.be/downloads/0/i...nual_k1823.pdf

I am using 220V-12V 2A AC transformer. The only deviation from the
above circuit is the use of a bridge rectifier W02 8169, Cermet Preset
Pot. Also the capacitors C1 and C3 are disk and Tant. respectively,
but values are the same.

At what voltage the Pot. should be set so that when I connect it to
the bread board, I would get 9V throughout. Thank you for your help.

You really need/want a decent voltmeter for that - you adjust the pot
for the voltage out. (BTW I couldn't see the website with the link
you supplied)_ any problem with just getting and using a three
terminal regulator that is designed to put out 9V?

Somewhere in this electronics stuff there has to be a "standard" In
days of yore they used something called a "standard cell." As long as
the chemistry was working, and you didn't load it too much, it output
a KNOWN voltage. We used something called a "differential voltmeter"
that could take the voltage that the standard produced and compare
that to an input (unknown voltage). They depend on precise resistors
in a "decade" box to compare voltages. (and it is still done that way
today in labs that certify equipment)

The more important thing is to ask how critical are you that this be
9.000 volts? Would 9.6000 or 8.4000 be close enough?

The voltage drop of a silicon diode is about 0.6000 with just a little
current (0.001 amps) flowing through it. Like the idea of using
LED's - enough diodes can be a "standard".

Want to just replace a nine volt battery? Get a 9 volt battery and
put a 100 milliamp 2 volt bulb between the two sources. Adjust for
zero light. You put a load on your constructed power supply (as heavy
a load as it will take) put the bulb between the 9 V battery and PS
(+ to +) and tweak until the bulb goes out/comes on - then set if for
the approximate middle.

Or hell - unless it is a critical application, 12 volts may work - how
close to 9 does it have to be, and why?

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