LM317 Power Supply Design. (SOLVED)

[Mint.]

Well I am designing an Lm317 voltage regulator, however I am a bit stuck. I have no idea how much current the lm317 needs to operate, and I cannot find it on the data sheet. I need this to understand what wattage to pick for resistors. I am planning to power this from 12v dc charger that supplies 3A, will I need to place some kind of resistor before the Vin? Or is the 50ohm resistance enough inside the 317?
See attached picture for circuit.

[vk6hdx]

I have no idea how much current the lm317 needs to operate, and I cannot find it on the data sheet.

Hi Mint, are you referring to the quiescent current?  If so this is available on the datasheet.  Otherwise the current required by the 317 @ vin will be proportional to the current drawn @ vout.

No need to use a currently limiting resistor on vin as the 317 has all the internal protection it needs.

[Mint.]

I have no idea how much current the lm317 needs to operate, and I cannot find it on the data sheet.

Hi Mint, are you referring to the quiescent current?  If so this is available on the datasheet. Otherwise the current required by the 317 @ vin will be proportional to the current drawn @ vout.

No need to use a currently limiting resistor on vin as the 317 has all the internal protection it needs.

Perfect! Thanks!

[metalphreak]

That is also where you get the value for power dissipated by the regulator. Current in is the same as current out, combined with the voltage drop across the regulator (Vin - Vout), gives you the power dissipated.

P = (Vin - Vout) x I

The greater the different between input and output voltages, the lower the efficiency as the regulator consumes more power.