Well, curve might be misleading since it's most often linear. Diodes of all sorts often have an inverse Vf vs. I know this thread is getting old, but I just wanted to add a point for future readers. What makes LEDs sometimes turn on and sometimes not?ĭoes this behavior indicate that either one or more of the LEDs are actually damaged, or is it more likely that there's a lose connection somewhere? Also, most connection points are covered with conformal coating and I am now suspicious if the coating puts stress on some of the solder joints) (Obviously, there could be, as the boards are handsoldered. There is no visible sign of a broken solder joint or lose wire connection. I go back to connect the 9V in connection A (at connector) and suddenly all LEDs work from here as well.Then I test connect 9V at connection B (directly on the solder joints on the PCB) and now all LEDs work.I test connect 9V in connection A (at connector) and only half the LEDs work.What I now want to understand is the behavior I observe when debugging those faulty boards: Outside the setup, i test them with a 9V power supply. In the proper setup those LEDs are driven with a LED PWM chip. In an installation with several of those PCBs, I've experienced that after a while a few of them only light up half the LEDs. The PCB has wires soldered onto it that go to a connector about 10cm down the line. I have a small PCB that holds 6 LEDs ( model, fV 3.2V, 30 mA), 2 parallel lines of 3 LEDs in series.
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