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Brians256 · 11-05-2002, 06:32 PM

Be careful, though. Too much capacitance will turn the PWM fan control into a DC-to-DC converter. You will end up with a variable output (unregulated) switching power supply. Kind of like the 12VDC rail on most cheap PC PSU's. Well, I take that back. I think it's the 12VDC rail that's unregulated. It might be the 5VDC rail.

In other words, large amounts of capacitance will smooth out the PWM output such that the pulses are gone. Instead of having peaks at 12VDC and a 25% duty cycle, you will have a smooth 3VDC feeding into the fan. The fan will not run on 3VDC, but it WOULD run on a 25% duty cycle PWM waveform.

11-05-2002, 06:32 PM	#15
Brians256 Pro/Staff Join Date: Oct 2001 Location: Klamath Falls, OR Posts: 1,439	Be careful, though. Too much capacitance will turn the PWM fan control into a DC-to-DC converter. You will end up with a variable output (unregulated) switching power supply. Kind of like the 12VDC rail on most cheap PC PSU's. Well, I take that back. I think it's the 12VDC rail that's unregulated. It might be the 5VDC rail. In other words, large amounts of capacitance will smooth out the PWM output such that the pulses are gone. Instead of having peaks at 12VDC and a 25% duty cycle, you will have a smooth 3VDC feeding into the fan. The fan will not run on 3VDC, but it WOULD run on a 25% duty cycle PWM waveform.