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Old Jun 20, 2005, 05:04 PM
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Hastings, New Zealand
Joined Jan 2001
5,217 Posts
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.

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).

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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