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Altera_Forum
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14 years ago

Using LM317 to power FPGA

Analysing a couple of schematics I found out some using this device. Declared input voltage is 5..9v. Research of datasheet for LM317 shows that Vin-Vout should be >3v. Thus it will not be possible t...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
14 years ago

Suppose to have a 12Vdc.

You want to connect a fpga and all the hardware around.

It's very easy to reach 1A (317 is limited at 1A)... However suppose to have only 700mA..

the hardware want 3.3Vdc.

So it drop 12-3,3 = 8.7V on 317.

The power dissipeated by the 317 is 8.7*0.7 = 6W!!!!!

You throw away 6W!!! And you hardware use only 2.3W

Ever you start with 5Vdc there is 1.2W dissipated that is comparable with 2.3...