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Honored Contributoruser LED circuit on EP3C120F780 development kit
Hi,
I checked the schematics of user LED ciruity on EP3C120F780 development board, the ciruit seems weird to me. The LED anode is connected to 3.3 through 56 ohm resistor and the cathode connected directly to FPGA pin: (led) 3.3 [V] | (pin) o---|<]----www--` 56 [ohm] What the voltage drop on the LED when it is on and when it is off? LED on: When FPGA drives '0' (LED is on) and, say the voltage drop on LED is 0.7 , the resistor current will be (3.3 - 0.7)/ 56 ~ 50 mA which seems to much ... LED off: Now the pin is connected to bank 4 which has 1.8 I\O voltage so how the LED is turned off ?3 Replies
Altera_ForumThe attempt to draw the schematics didn't come off well
I'll try again, (dots are just to fill space) .................(led)..........3.3 [V] ....................................| ....................................| ...(pin) o----|<]---www--` ..................................... ........................56 [ohm]- Altera_Forum
a LED does not have a voltage drop of 0.7V.
Depending on the color, you have a voltage drop of about 1.9 to 3.5V. see https://secure.wikimedia.org/wikipedia/en/wiki/light-emitting_diode - Altera_Forum
Ok, Thanks!
