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LED Voltage Drops

Posted by jpluimers on 2019/09/19

[WayBackDangerous Prototypes: Basic Light Emitting Diode guide – Voltage drop or forward voltage has a nice table of common LED types:

You can also measure them yourself using most multi-meters have setting for that as described in [WayBack] Easy way to figure out a LED’s Vf in order to pick an appropriate resistor – Electrical Engineering Stack Exchange

You can also measure yourself, but my Proster VC99 multi-meter (cheap, but functions well, see for instance the review in [WayBack] MagPi issue 43) can measure voltage drop, so I’ve measured some LEDs from old PC cases:

  • Red: 1.8 V
  • Yellow: 1.8 V
  • Green: 1.8 V
  • Blue: does not measure

Given that they all have the same voltage drop, I made the below table with some resistor values to get the same current through them on various voltages (3.3V, 5V and 12V) based on Standard resistor values.

Note anything less than 20mA of current usually is OK (though 20mA often is on the bright side).

LED Colour Voltage drop (Vf) Total Voltage Remaining Voltage Resistance Ω Current mA Power mW
Any 1.8 5 3.2 220 14.55 46.55
Any 1.8 12 10.2 680 15.00 153.00
Any 1.8 3.3 1.5 100 15.00 22.50
Any 1.8 5 3.2 330 9.70 31.03
Any 1.8 12 10.2 1000 10.20 104.04
Any 1.8 3.3 1.5 150 10.00 15.00
Any 1.8 5 3.2 470 6.81 21.79
Any 1.8 12 10.2 1500 6.80 69.36
Any 1.8 3.3 1.5 220 6.82 10.23

Background for doing these calculations:



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