I was putting diodes in a pot of boiling water this morning. No, it's not a hangover cure. I was just trying to get an idea of whether led's have the same temperature coefficient as "regular" diodes. So I made a series of 1N4148's, put 8 mA through it, and measured voltage drop at room temperature and boiling. Did the same, at 8 mA, with a string of cheap pink led's. I assumed a change from room temp to boiling of 75 degrees centigrade (didn't have a thermometer). The 1N4148's and the led's came out to have very nearly the same tempco, they were both between 2.00 and 2.05 volts per degree centigrade per diode. Also pretty close to the tempco figures I've seen cited in the literature of about 2.1 or 2.2 mV/C. I then put 19 mA through the 1N4148's and got a much lower tempco of 1.56 mV/deg C. I'm wondering if this is because (A) 19 mA was enough to warm up the diodes, throwing everything off, (B) tempco really varies that much with current, or (C) my kitchen experiment was too sloppy.
17 years ago