On Sat, 27 May 2006 10:22:12 GMT, bigdaddy
wrote:
On Fri, 26 May 2006 16:26:41 -0400, default wrote:
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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Yes I want round about 9 Volts. The point is, Its being voltage
regulator, it is not doing its job. There are no lose connection or
dry connection for that matter. I do have digital volt meter and I did
tweak the pot to 9 volts but when I connect it to the board with a
basic 555 circuit I get 6.51 volts at the terminals, but with a 9 volt
battery I get 8.47 volts.
The 120 ohm resistor is not exact, but wouldn't the pot compensate for
that. There is a heat sink attached to the LM317 firmly with
conducting paste in between and the heat sink remains cool.
Thanks for your help.
Oh - I had a similar problem not so long ago. It was the 3 amp TO3
style adjustable regulator - would regulate as far as the output was
concerned but would fall off rapidly when any kind of current was
required. Heat sink stayed cool. PS is ~20 years old and had worked
fine all that time.
My biasing resistor had opened up. The 133 ohm resistor between the
output and adjustment point and pot was reading over 2K. Check that
and check the connections.
Another possibility is that there isn't enough voltage going in to
maintain regulation. For nine out you want about 13 volts input (and
that is to "the valley of the ripple") Check the input with and
without a load.
As a rule of thumb I use 2,000 microfarads for every amp of current
for around 10% ripple, at 60 HZ. Electrolytic caps have loose
specifications but they usually err on the side of more capacity than
the label reads.
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