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Re: How to caliberat voltage regulator

 Subject: Re: How to caliberat voltage regulator bigdaddy Tue, 23 May 2006 11:35:23 GMT sci.electronics.basics
 ```On 22 May 2006 13:19:44 -0700, "Chris" wrote: > >stratus46@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 ??? >> >> GG > >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). > >Good luck >Chris 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. ```
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