CO₂ Laser Tube Current: PWM Bandwidth

As with the analog bandwidth measurements, start with the same sine-bar bandwidth target:

Return the laser power supply’s IN terminal (and the purple wire to the oscilloscope) to the Ruida KT332N controller’s PWM output:

Engraving the pattern in grayscale mode at 254 dpi produces 0.1 mm pixels and makes each bar 1 mm wide:

Engraving at 50 mm/s = 50 Hz lets the laser current once again hit full scale:

The traces:

• 1 X axis DIR, low = left-to-right (yellow)
• 2 L-ON laser enable, low active (magenta)
• 3 PWM digital signal (cyan)
• 4 tube current – 10 mA/div (green)

The PWM signal runs at 20 kHz and presents itself as a rather blurred trace, but you can see both the general tendency and the discrete steps between the vertical gray bars. As far as I can tell, the signal never reaches 0% or 100%, most likely to prevent the PWM filters from saturating in either condition.

The tube current drops from 23.8 mA to 13.8 mA, just over the half-power level of 12 mA, at 200 Hz:

So the PWM bandwidth is a little over 200 Hz, slightly higher than the analog bandwidth of a little under 200 Hz.

All of the measurements as a slide show:

Now, with all the measurements in hand, maybe I can reach some sort of conclusion.