Hi Roger,

I don't think the Voltage waveform at the collector matters, since the LED operates from Current.

According to the datasheet, the LED has 25pf capacitance. So when you turn off the transistor, that voltage can only dissipate thru the relatively small leakage currents.

To allow the LED to discharge faster ... Placing a resistor across the LED would probably improve your waveforms, but it won't change the function and will only consume more current.

A better indication of the Drive Current would be to measure the voltage across the 33 ohm resistor. Which should be very "square".

DT