I have a 90mm, 12vdc, 200ma computer fan that I need to control the speed in an application unrelated to the computer. Power supply is 12v, 400ma. Does anyone have a circuit schematic that I could use to accomplish this. I tried the attached circuit with a 555 timer but I'm not getting any speed control with that circuit; just full speed. I believe these fans typically don't work well at voltages below 50%. I tried increasing the capacitance of C1 to bring the frequency down (on recommendation of circuit designer), but without any luck. I am an amateur here so I could use some help. Thanks!