LM317T Help!
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LM317T Help!
Of course, this is the n64 forums, so I want 3.3V. How can I set up the LM317T to spit out 3.3V with an input of 8.4V?
According to this http://www.electronics-lab.com/articles/LM317/[/url] you want to use a 240 for R1 and 400 for R2 but it doesnt sound right to me?... let me search a little more.
Edit: After some more searching... it looks like you can use a 200 ohm resistor for R1 and a 330 ohm resistor for R2 and you will get 3.31 volts and you should be able to find resistors in thoughs values pretty easily. It doesnt matter what voltage you use for an input, so long as its 1.5 volts higher than your output voltage your trying to get.
Good luck on your n64p.
-Hayden
Edit: After some more searching... it looks like you can use a 200 ohm resistor for R1 and a 330 ohm resistor for R2 and you will get 3.31 volts and you should be able to find resistors in thoughs values pretty easily. It doesnt matter what voltage you use for an input, so long as its 1.5 volts higher than your output voltage your trying to get.
Good luck on your n64p.
-Hayden
Last edited by Dr.Weasel on Sat Feb 18, 2006 12:25 am, edited 1 time in total.
http://www.fairchildsemi.com/ds/LM%2FLM317AHV.pdf
page 4 of the datasheet, input voltage doesnt matter as long as it's about 2V above whatever the output is
EDIT: darn...you beat me to it. Use values in the kilo-ohm range, it'll waste less power that way
page 4 of the datasheet, input voltage doesnt matter as long as it's about 2V above whatever the output is
EDIT: darn...you beat me to it. Use values in the kilo-ohm range, it'll waste less power that way
What I have shown you is reality. What you remember, that is the illusion.
"Say, what does this button do?"
All the dishes rattle in the cupboards when the elephants arrive
"Say, what does this button do?"
All the dishes rattle in the cupboards when the elephants arrive
Basically using higher resistors lowers the current that flows through the feedback portion of the circuit. If you use 200 and 330 ohm resistors, then at 3.3V there will be 6.2mA flowing through them, ignoring the adjust pin current. And unfortunately, power depends on the square of the current (p=i^2*R), so you'll waste about 20mW.
If you used 2k and 3.3k ohms, the ratio would be the same, but you would instead be pulling 0.622mA, meaning that you'd only dissipate 2mW. It may not seem like a big difference, but using a linear regulator you want all the effeciency you can get!
If you used 2k and 3.3k ohms, the ratio would be the same, but you would instead be pulling 0.622mA, meaning that you'd only dissipate 2mW. It may not seem like a big difference, but using a linear regulator you want all the effeciency you can get!
What I have shown you is reality. What you remember, that is the illusion.
"Say, what does this button do?"
All the dishes rattle in the cupboards when the elephants arrive
"Say, what does this button do?"
All the dishes rattle in the cupboards when the elephants arrive
eh...it doesnt really work that way unfortunatley. The 300mAh rating is the capacity (though 300 might be a typo, seems kind of small). The capacity rating means that one battery can supply 300mA for one hour before it is considered dead. If you put the batteries in series to increase the voltage the capacity stays the same, but if you put the batteries in parallel the voltage stays the same but the capacities add.
hope that helps
hope that helps
What I have shown you is reality. What you remember, that is the illusion.
"Say, what does this button do?"
All the dishes rattle in the cupboards when the elephants arrive
"Say, what does this button do?"
All the dishes rattle in the cupboards when the elephants arrive
The 300mAh is the current rating, not necessarily what the batteries will always put out current-wise. The system will take whatever current that it needs, provided that the batteries can supply it. (Sorry if you knew that already, since the question was pretty general; might as well cover all the bases, though).
So, for those batteries, if about 1.2A is being drawn, then for 6 of them in parallel, they'll last for about 1.5 hours (not considering any power loss from the regulator here). But, for the LM317, didn't Dr.Weasel say that you'll need at least 1.5V above 3.3V (I didn't use one, so not sure what would be good enough)? You'd need four in series for 4.8V then, and to get a high enough rating you'd probably need 6 sets of 4 in parallel. Twenty-four batteries just for the 3.3V line seems pretty inconvenient, especially since they'll only last about 1.5 hours, depending on the game.
So, for those batteries, if about 1.2A is being drawn, then for 6 of them in parallel, they'll last for about 1.5 hours (not considering any power loss from the regulator here). But, for the LM317, didn't Dr.Weasel say that you'll need at least 1.5V above 3.3V (I didn't use one, so not sure what would be good enough)? You'd need four in series for 4.8V then, and to get a high enough rating you'd probably need 6 sets of 4 in parallel. Twenty-four batteries just for the 3.3V line seems pretty inconvenient, especially since they'll only last about 1.5 hours, depending on the game.
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