Aaaand the tube current doesn’t have a nice clean rising edge, so I think the “≤1 ms” spec applies to a resistive test load, not an actual CO₂ laser tube.
The traces:
- Yellow = X axis
DIRsignal for scope sync - Magenta =
L-ON= negative-active Enable - Cyan =
IN= analog voltage 2 V/div - Green = tube current 10 ma/div
Over on the left side, the L-ON signal goes low with the IN signal high for the first bar of the test pattern. The tube current jumps from 0 mA to a huge off-screen-high value, then rings like a bell for maybe a millisecond before settling down.
Yeah, we all switch L-ON for a millisecond or two, but the tube current has nothing to do with any reasonable assumption based on the good old single-pole risetime we all think should describe it.
So the PWM (and analog) inputs have a low bandwidth and the Enable signal isn’t much, if any, faster.
We just assume everything works the way we think it should, but the truth is that we’re just putting up with whatever it does. 