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Old Jun 20, 2005, 05:04 PM
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Hastings, New Zealand
Joined Jan 2001
5,217 Posts
Quote:
Originally Posted by Joel
I was wondering why you didn't just use 6 N-channel MOSFETs instead of Ns driving Ps?
To use high-side N-Channel FETs efficiently you would have to boost the pre-driver's power supply to at least 6V higher than the supply voltage.

Quote:
Also what hall sensors do I need? I'm guessing bipolar analog? 4pins?
CDROM motors have the the 4 pin analog (differential output) sensors built-in. To use single-ended Hall sensors, you would have to bias the other input to match the sensor's quiescent output level (perhaps with a trimpot connected across the sensor's power supply pins).

Quote:
if I'm not using any of the power, will the high voltage jump from the source to the gate? Is that what the Vgs is? How would I get around this?
Vgs is the maximum allowable voltage from Gate to Source. If the FET drivers are off then it should be zero. On-state Gate voltage is determined by the drivers. Usually the low-side is safe, as it will be less than the pre-driver's Vcc (regulated if necessary).

To protect the high-side FETs you could add some resistance in series with the Gate, and back-to-back zener diodes (or a transient suppressor diode) from Gate to Source.
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