Nigel Goodwin said:
(which you could then buffer with a driver transistor to feed the motor).
OK, that's a new term to me. Is that the same thing as a VFET? In other words, a power transistor, which instead of turning on and off, tracks the control's voltage?
I've been searching patents and I found a diagram of what is claimed to be a "simple PWM controller". It's very similar to what you are saying. Basically, a capacitor across the load, and an inductor (or rectifier?), but the inductor is in series
before the capacitor. Finally, it has a low-side transistor which I assume is turned on when the high side is off. So in other words, you create A/C. I guess the inductor needs to be able to draw current from ground when the PWM signal is switched to low.
**broken link removed**
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Here is a description of the circuit from the patent:
"Electrical power for an integrated circuit (IC) is typically supplied by one or more direct current (battery) power sources, such as a pulse width modulation (PWM)-based, DC-DC converter. As diagrammatically illustrated in FIG. 1, this type of converter contains a PWM signal generator 1 that supplies a synchronous PWM signal to a switching circuit driver 2. Such a PWM-based converter architecture is ideally intended to deliver constant energy to an output node regardless of the input voltage. To this end, the switching circuit driver 2 controls the on-time and off-time of a pair of electronic power switching devices 3 and 4 (typically external NFETs) connected between power supply rails Vin and ground (GND). A common or PHASE node 5 between the two FETs is coupled through an inductor 6 to a load reservoir capacitor 7, with the connection 8 between inductor 6 and capacitor 7 serving as an output node from which a desired (regulated) DC output voltage is applied to load 9"