Quote:
Originally Posted by serialk11r
You bring up a good point, with 3 pole pairs that would correspond to a max alternator rpm of 6000, which is not very high.
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So, above 6000 alternator rpm, or above 2000 engine rpm, the very worst case scenario is that the MOSFETs would act like normal rectifier diodes. That might not be good for people who normally cruise at an engine speed above 2000 rpm.
I went by the description of the duty cycle given by the data sheet, because while TI gave the graphs to show why they came to 300 Hz, they neglected to give their test circuit. V(gs-threshold) appears to a heavy factor in the arrival of that figure.
It would appear that TI arrived at its 300 Hz figure to say that 300 Hz was the highest frequency at which their rectification circuit would deliver an output comparable in waveform to an equivalent diode rectifier circuit. Beyond that, the charge time would start to eat into the upswing of the AC waveform, distorting it significantly. Again, though, the MOSFET would act like a diode duting this time, so rectification would still take place. I can live with that.
I'll post a few pictures illustrating this, later on.