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A voltage regulator's workins (help!)

chottu

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:-?

hi all. i hav a question bout the lm317t used in daedal's circuit.the pin on the righ is the one to which voltage goes in , right? and the one in the middle out...and the one on the right is.....well i dont know which is why im askin.wat does this adj do ? if i am 2 use this in another circuit how would i hav 2 set it up.wat i think is that the +from the battery should go 2 v in and the the vout should be connected 2 the vthe - of the battery , right?But i dontknow what the adj is for and why we have to connect it 2 the vout in ddl circuit?

thnx in advnce!!

i will also be askin about a pot's workin's the next time.
 





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Firstly I am unsure of what you are asking....
Title says voltage regulator...why do you want to regulate voltage?
Are you running one LM317 from the other one so that the first reduces the voltage to the second one?
The adj is adjust...which adjusts the output by using a resistor.

In its simplest form the circuit looks like this.....
 

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chottu

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thanks 4 thee reply!!

srry for not being clear. but i want 2 regulate the current bcuz in daedal's guide he wrote:


What?
The voltage source that this circuit is designed to regulate is one supplied by an alkaline/lithium battery. An AA/AAA/AAAA battery supplies approximately 1.5 Volts DC(usually more around 1.2 for lithiums, but I've had a few at about 1.6-1.8!!). A CR123A battery supplies 3.0 or 3.6 Volts DC depending on the battery. This is very useful and very stable for the most part. When a battery is left unused for a while, the first burst of energy dispelled from the battery can spike up to 10 times the average power of the battery! Therefore, for a 1.5V battery, this would add up to approximately 15V. This burst is very small and very short that in most situations would not even kill the laser diode, but there are times when the burst packs some power along with it, supplying well over a watt of energy to the diode. This can spell instant death for most diodes!

How?
To regulate the voltage we can either use a voltage regulator and set it up in voltage regulation mode and limit the supplied voltage(This would still miss some of this spike and still pass it on to the diode) or we can use a capacitor. Capacitors work by charging up when there is a change in voltage. Direct Current voltage turns a capacitor into an open-circuit (a cut wire), and thus any spike or change in line regulation would work first on charging up this capacitor. Capacitors have 2 readings on them that correspond to maximum voltage and capacitance. For most of my applications I use a 47uF 16V capacitor. To be more on the safe side, you can get a higher capacitance and a higher voltage rating, but it all depends on personal preference. A capacitor will work to regulate the line up to the maximum power that it can soak up as fast as it could. Capacitors ADD up when connected in PARALLEL. Therefore, if you want to use mutiple capacitors with different benefits (Max voltage and big capacitance for instance) you need to make sure that BOTH positive and negative leads on the capacitors are connected together. I will explain more detail later on.



so i want to regulate the voltage so as to protect my diode.
nyway thnks 2 yr diagram i understood the thing that was bothering me the most(what adj is for).
So how do i calculate the output according to the input??should i use ohms law(v/i = r)?if so how?
 
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I hate to be picky but I don't do text speak, plain english please.

If you are going the voltage regulation route you will need to find the data sheet for the LM317 as it is a combination of resistor values to set it up, the circuit looks like this......
 

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chottu

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REALLY SORRY FOR EATING UP YOUR TIME BUT I REALLY WANT TO TRY THIS OUT ;)

anyway being a 12 year old and having absolutely no previous knowledge of this stuff , this time the diagram made absolutley no sense :p. (and it had absolutely no plain english either.hehe)

i think i just figuired out something.but am still not sure about it.in daedal's circuit is the lm317t used as a Current regulator? In daedal's circuit he doesnt regulate voltage does he?he only dampens the spikes using the capacitor right?So he uses the lm317t to regulate the current and attaches the pot and two resistors to the ADJ and v-out so as to be able to control the amount of resistance.is that correct?

Another doubt - what would happen if there was the pot and the two resistors and there was no lm317t?wouldnt the pot still be able to regulate the current?what difference would the lm317t make? Is it necessary that for a pot to be used it has to be connected to the lm317t?

thanks for replying again and again.i hope it continues(i tend to have the habit of irritating people with question after question.anyway those were only my 7th standard science teachers.and even after that i didnt learn anything about this from them , just got more confused.no one to ask questions about these things except you guys.And things get even worse when theres no radioshack in the uae - thats where i live.and being only a kid im not allowed to buy anything online and hav only a limited amount of money. But i hav managed thnx to u guys)
 
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chottu said:
REALLY SORRY FOR EATING UP YOUR TIME BUT I REALLY WANT TO TRY THIS OUT ;)

anyway being a 12 year old and having absolutely no previous knowledge of this stuff , this time the diagram made absolutley no sense :p. (and it had absolutely no plain english either.hehe)

i think i just figuired out something.but am still not sure about it.in daedal's circuit is the lm317t used as a Current regulator? In daedal's circuit he doesnt regulate voltage does he?he only dampens the spikes using the capacitor right?So he uses the lm317t to regulate the current and attaches the pot and two resistors to the ADJ  and v-out so as to be able to control the amount of resistance.is that correct?

Another doubt - what would happen if there was the pot and the two resistors and there was no lm317t?wouldnt the pot still be able to regulate the current?what difference would the lm317t make? Is it necessary that for a pot to be used it has to be connected to the lm317t?

thanks for replying again and again.i hope it continues(i tend to have the habit of irritating people with question after question.anyway those were only my 7th standard science teachers.and even after that i didnt learn anything about this from them , just got more confused.no one to ask questions about these things except you guys.And things get even worse when theres no radioshack in the uae - thats where i live.and being only a kid im not allowed to buy anything online and hav only a limited amount of money. But i hav managed thnx to u guys)

I posted the Data Sheet above.... you will need to look at it.... It is the Bible for the LM317 Regulator..
It was written by the people that designed it...

On page #1 is a circuit for a Voltage Regulator.... and on page #9 is a circuit for a
Current Regulator... not the differences between the 2 circuits... then you will understand the
2 drawings that "rog8811" posted... :cool:

Jerry
 

chottu

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thnx,, but i dont need the voltage regulator diagram as i figuired out that in daedals circuit the lm317t is used as a current regulator anyway i still want to clear these hings up-

Another doubt - what would happen if there was the pot and the two resistors and there was no lm317t?wouldnt the pot still be able to regulate the current?what difference would the lm317t make? Is it necessary that for a pot to be used it has to be connected to the lm317t?

anyway i stil will hav a look at the datasheet.
 
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It might be easier for you if you ignored how these things worked, and just built it according to the diagrams... Once you've taken a few more years of math and a couple basic electronic courses, then maybe you'll be able to grasp what's going on inside a driver, but for the meantime I get the feeling that trying to explain things to you will only confuse you further.

Also, may I suggest you use a spell checker for your posts? It would make deciphering them much easier for us. U kno cuz itz hrd 2 figger owt wut u meen wen U tyep liek dis.
 
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If you don't use the LM317 regulator in the circuit the current will change
as the battery drains... The LM317 compensates for that... until the battery
reaches the LM317's dropout voltage...

All explained in the Data Sheet............. :cool:

[Edit]
  "pseudolobster" has a point... you need basic electronics knowledge
to fully understand the inner workings of the LM317...

Jerry
 




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