For this objective, I built an actual PWM low-power AM transmitter. The details of the actual work and the circuit itself are so many that a detailed discussion is beyond the scope of this article.

Figure 1 PWM amplifier circuit built around a two quadrant driver circuit. Here, R1 and C1 make up a modest filter for transistor Q4. 3.3V at the emitter of Q5 will reverse bias base-emitter junctions ...

Looking at the circuit diagram, the "+12V" and "0V" terminals connect to the respective connections on the PSU Molex connector. The "FAN+" and "FAN-" connect to the corresponding +v and -v ...

The back EMF, along with the RL circuit in a brushed DC motor, brings non-linearity to the PWM control and the PWM frequency and PWM duty cycle become significant for getting the best output power.

It also inverts the duty cycle, so that 100% drive to the fan occurs when the PWM output is at 0V. Figure 2: This circuit improves the standard approach of Figure 1 by including a low-pass filter that ...

1. Shown are a series resonant circuit (a) and parallel resonant circuit (b). On the other hand, the parallel resonant LC tank’s impedance is maximized at resonance.