I'm working on a system that was designed to light incandescent lamps in a matrix. When the lamps are replaced with LED bulbs, they light dimly when they're not supposed to. These bulbs include the current limiting resistor and a rectifier to allow them to be used with AC.
I've narrowed the matrix to a single bulb, 18VDC switched by a TIP107, GND switched by a TIP102, and the controlling circuit. I can turn on the 18V, for 300 usec, off for 1 ms, GND on for 300 usec, off for 1 ms. At no time are both transistors on, but the LED bulb still lights dimly. I have verified with a scope that the controlling logic timing is correct.
Should I be looking at current leaking through the transistors when they're off? A capacitance source somewhere? Other ideas?
I've narrowed the matrix to a single bulb, 18VDC switched by a TIP107, GND switched by a TIP102, and the controlling circuit. I can turn on the 18V, for 300 usec, off for 1 ms, GND on for 300 usec, off for 1 ms. At no time are both transistors on, but the LED bulb still lights dimly. I have verified with a scope that the controlling logic timing is correct.
Should I be looking at current leaking through the transistors when they're off? A capacitance source somewhere? Other ideas?