On 22 May 2006 13:19:44 -0700, "Chris" <cfoley1064@xxxxxxxxx> wrote:
>> 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/illustrated/illustrated_assembly_manual_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.
>> Try presetting the pot to 744 ohms with a digital meter. OR, power it
>> up and adjust the output to 9 volts. 744 assumes the 120 ohm resistor
>> is exactly 120 -- they rarely are. Either way, you need a meter and if
>> you intend to do more of this, you NEED a meter. Prices start from $5
>> to ???
>Bigdaddy, GG's right. One other thing -- the reason it's called a
>voltage regulator is that the voltage stays almost exactly the same if
>the load current is small or large. For the LM317 with a 120 ohm
>resistor, it stays the same even if there's no load.
>So, get a voltmeter. Power up your regulator circuit with *no load*
>connected, and tweak in the pot to the right output voltage. Then
>you'll know it will keep 9.0V for any reasonable load (but make sure
>you put a good heat sink on the LM317 to keep it from getting too hot).
That is my point. Its being voltage regulator, it is not doing its
job. 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.