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Old Nov 12, 2004, 01:38 AM
jeffs555 is offline
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"Simplify, then add lightness"
Joined Nov 2000
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There are several problems with using mosfets like you show. The first thing is that driving directly from the logic that way, your motor voltage could be no higher than your logic voltage, or the top mosfets would never turn off. Also, mosfets have very high input capacitance, so at a bare minimum, you would need a series resistor to limit the current from the logic to prevent damage to the logic and you would have slow switching times on the mosfets which would cause them to heat up more. Also, you generally would use nmos for the bottom mosfets. The way you have it shown with pmos on the bottom in the common drain configuration, the bottom mosfets would never fully turn on. To turn them on fully you would need to drive the gates below ground.
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