Originally Posted by doyll
Fan rpm at PWM % is based on fan max speed and PWM%:RPM curve.
For example here is a graph of TY-14x series fans. Notice the TY-140, 147 & 147A are all 1300rpm, but TY-147A has a different curve than the other two because the PWM program is different allowing it to idle at 300rpm and ramp up faster above 900rpm. The TY-143 is 2500rpm with same PWM program as TY-140 & 147, but because of the difference in maximum speed spins faster on same PWM signal.
I would use F12 fans as intake and on cooler with A12S as exhaust. This will give a slight advantage to intake airflow to overcome filter and more restrictive vent grill than exhaust and leak filtered air out of case to balance the pressure rather than dusty air leaking in when exhaust is pulling more than intake is supplying.
There are many different pulse signal designs being used now to stop the pulse click and fan noise. Some even have a varied spacing rather than consistant spaced pulse beat to vary the power to fan.
The simplest way to generate a PWM signal is the intersective method, which requires only a sawtooth or a triangle waveform (easily generated using a simple oscillator) and a comparator. When the value of the reference signal (the red sine wave) is more than the modulation waveform (blue), the PWM signal (magenta) is in the high state, otherwise it is in the low state.
A simple method to generate the PWM pulse train corresponding to a given signal is the intersective PWM: the signal (here the red sinewave) is compared with a sawtooth waveform (blue). When the latter is less than the former, the PWM signal (magenta) is in high state (1). Otherwise it is in the low state (0).Delta
In the use of delta modulation for PWM control, the output signal is integrated, and the result is compared with limits, which correspond to a Reference signal offset by a constant. Every time the integral of the output signal reaches one of the limits, the PWM signal changes state.
Principle of the delta PWM. The output signal (blue) is compared with the limits (green). These limits correspond to the reference signal (red), offset by a given value. Every time the output signal (blue) reaches one of the limits, the PWM signal changes state.Delta-sigma
In delta-sigma modulation as a PWM control method, the output signal is subtracted from a reference signal to form an error signal. This error is integrated, and when the integral of the error exceeds the limits, the output changes state.
Principle of the sigma-delta PWM. The top green waveform is the reference signal, on which the output signal (PWM, in the bottom plot) is subtracted to form the error signal (blue, in top plot). This error is integrated (middle plot), and when the integral of the error exceeds the limits (red lines), the output changes state.Three types of pulse-width modulation (PWM) are possible:
The pulse center may be fixed in the center of the time window and both edges of the pulse moved to compress or expand the width.
The lead edge can be held at the lead edge of the window and the tail edge modulated.
The tail edge can be fixed and the lead edge modulated.
Three types of PWM signals (blue): leading edge modulation (top), trailing edge modulation (middle) and centered pulses (both edges are modulated, bottom). The green lines are the sawtooth waveform (first and second cases) and a triangle waveform (third case) used to generate the PWM waveforms using the intersective method.