It means pulling to GND as well, not leaving open circuit.
Sorry, I still don't get it. I thought my last 2 circuits were closed. I only put the GND in because LTSpice requires it.
It sounds like a really fun discussion but are you sure you're not going a little OTT just to stop a fan whining?
Presumably the PWM changes in response to some kind of temperature sensing, so as long as the fan control range is able to keep up, then is there a problem?
Just asking.
On the contrary, I'm sure I'm going completely over the top. At this point it's mostly just a fun learning exercise.
The PWM doesn't actually adjust to temperature, it's purely software-controlled and it can be configured at will. This is the part cooling fan of a 3D printer, it blows air over the molten filament exiting the nozzle.
A common example would be to print the bottom layer with no cooling to improve adhesion to the print bed. After that you would use a middle-of-the-road fan speed depending on the temperature you're printing at and the material you're using. The bottom few dozen layers would still be printed at a higher fan speed to compensate for their proximity to the heated bed. If there is any bridging in your model you would use 100% fan speed for those lines because the faster they cool and become solid, the less hanging there will be. So yea, it varies throughout the print.
The bottom line is that pretty much the entire spectrum of the speed control gets used, and that most of the time you're not running at 100% which means the whining noise is always there. It doesn't matter what the duty cycle is, the noise is caused by the PWM frequency so it makes a constant ~500Hz tone at any speed below 100%. Not ideal to have next to your bedroom during a 24h+ long print.