I got the LM317T from Radio Shack and I am trying to wire up an external battery pack to run an mp4 player which has an internal 3.7v battery.
Can someone explain to me (in plain english, I'm new with this stuff) what I need and how to adjust this thing? I want to run this mp4 player on a rechargable 9.6v battery that I have.
Thanks in advance.
Try the 1st circuit on
You'll need 192 ohms for R2
Ok well I'm a total "noob" at all this but I think that diagram makes sense. I'll see what I can make of it. Thanks.
Be aware that you'll burn up much of your power in the LM317. So don't expect long battery life with this method.
In plain English: The output pin regulates to a voltage that is 1.25V higher than the voltage on the ADJ pin. The two resistors form a voltage divider to set the ADJ pin voltage. You can use the formula on this page
To compute the values of the resistor.
It won't last long. You really need a switching regulator to get any real usable battery life.
BAJ
What more can you tell me about a switching regulator? What would it take to use one of those instead of the LM317T?
Switching regulators make a lot of noise. You might get better sound with the LM317. The battery life will be a about 1/2 as much compared to a switching regulator since the input is about twice the output.
Basically, a switching regulator charges a capacitor very quickly to the desired output voltage and then waits for the capacitor voltage to fall a small amount and then blast it again with a pulse of current to bring the voltage back up. It sort of switches on and off as necessary to keep the output fairly constant. But it won't be as smooth as the linear LM317 and so needs more filtering on the output to get rid of the noise and small variations in output voltage.
-Bill
Here's a "picture".
+-----------------------> Gnd To MP3 (-) | ------ | --------- +---|470ohm|---+---|-BATTERY+|---+ | ------ --------- | | | | ------ | | | o | | | |______| | | /______/| | | | || | | |LM317 |/ | | ------ | | | | | | +----------+ | +---------------+ | | | | | ------ | +---|240ohm|--+------------------------> 3.7V To MP3 + ------With the 240 and 470 resistors shown, you'll be within .003 volts of target (3.7) per the computation. You do not need any capacitors if you keep the LM317 relatively close to the battery.
Ed
Thanks a lot. So far that is working perfectly. I will post a link to my project once I have the site up, for anyone who is interested.
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