03-04-2014, 10:14 AM
Yes, that's pretty much correct. You are starting out with a 23V supply. subtract from that the 2.2v LED drop and another .5 v for the saturation voltage drop of the switch transistor on the MPX board. That leaves you about 20v left. You also have the voltage drop across the 220 ohm series resistor. So neglecting the 10K, you have 1500 + 220 (or 1.72k) across a 20v supply which by ohms law results in a LED current of 11.6 mA.
So there is about 2.4v drop in voltage across the 220 ohm resistor compared to 8 v with the original bulb ( 23v down to 15v)
So there is about 2.4v drop in voltage across the 220 ohm resistor compared to 8 v with the original bulb ( 23v down to 15v)
