Driving MOSFET gate from logic outputs

Would a common base transistor configuration be a good way to drive the gate of an N-MOSFET from a logic output?

The MOSFET is the high side of an H-Bridge sitting at about 40V. The gate will be drawn to 48V which is much too high for logic outputs. Since I want to run the bridge with high inputs it seems that a common base configuration would give large voltage amplification in phase with the inputs. The output of the logic gate would be fed into the emitter and the collector would hook to the MOSFET gate (and +48V through a current limiting resistor. I'm not positive but it seems as if a resistor between the collector and the gate would be a good idea as well.

In reading about this configuration several references stated that it's normally used in RF circuits because of the large voltage amplification. The bridge is to be PWM driven at possible tens of KHz but nowhere near RF. Is there something I'm missing about this that would make it unsuitable for this application? Insights, suggestions and hints are all welcome!



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The common base stage can be used to level shift and voltage amplify the logic swing, but it provides little drive current to quickly charge and discharge the gate capacitance. You will probably need to add a complementary emitter follower to provide this current capability.

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John Popelish

I use mos driver IC's for low and high side switching. D from BC

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D from BC

Consider one of these???

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It drives the high and low side of half the H-bridge. Two logic inputs so you can control the dead time, etc. Bootstrap circuit allows use of N-chan mosfets. They have a whole family of devices that might be better for your particular application. I believe you could run the whole H-bridge from one driver if you wanted. They even have versions with the MOSFETs built in. Watch out for leakage on the bootstrap cap @ 100% duty cycles.

-they call me frenchy.

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They call me Frenchy!!

You could use opto isolators to drive the gates of the FETs.

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