Extrait d'un post pinside, pour la traduction je vous laisse faire :
It gets pretty complicated pretty quick. When you look at the lamp voltage with a multimeter, you're just seeing the average voltage. What's actually happening is the 18VDC source is being turned on and off lots of times a second.
Looking at it with an oscilloscope, you can see that when the controlling signal tries to turn a column off, it takes a while before it actually happens. The green line is the transistor output, and the yellow line is the controlling signal.
First, you can see a delay from when the input (yellow) goes high to when the output (green) goes low. Second, notice that the output doesn't actually go all the way to 0V. It decays off over time, and the amount of time this takes is dependent on multiple factors. This is happening on BOTH the column and row side of each lamp.
It gets pretty complicated pretty quick. When you look at the lamp voltage with a multimeter, you're just seeing the average voltage. What's actually happening is the 18VDC source is being turned on and off lots of times a second.
Looking at it with an oscilloscope, you can see that when the controlling signal tries to turn a column off, it takes a while before it actually happens. The green line is the transistor output, and the yellow line is the controlling signal.
First, you can see a delay from when the input (yellow) goes high to when the output (green) goes low. Second, notice that the output doesn't actually go all the way to 0V. It decays off over time, and the amount of time this takes is dependent on multiple factors. This is happening on BOTH the column and row side of each lamp.