What would happen if I didn't use MOSFET gate a driver, and simply connected the MOSFET gates directly to the logic outputs of a microcontroller? I am quite confused about the need of a MOSFET driver.
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We need more information. A circuit would be helpful. What are you trying to do? – Feb 21 '13 at 10:31
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Re Rocketmagnet's 1. - To switch fast enough in the 10 kHz = 100 kHz range a MOSFET gate capacitor typically neds to be charged and discharged at 100 mA to 1A range. This is too high for gates or microcontrollers . If they are aused directly the current would be low and the switching times would be long - causing heavy switching losses. – Russell McMahon Feb 21 '13 at 11:39
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Possible duplicate - see http://electronics.stackexchange.com/questions/3348/what-is-the-purpose-of-mosfet-driver-ics?rq=1 – Adam Lawrence Feb 21 '13 at 13:30
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An H-Bridge contains 4 transistors. Often these are FETs. The gate of a FET is not as simple to drive as you might think, for two reasons:
FET gates have some capacitance, which takes a little while to charge up to the threshold voltage. This in turn means the FET take a little to switch on. While the gate capacitor is charging up, the FET is only partially on, and therefore dissipating power and getting hot. The faster you can charge that capacitor, the faster you can switch it on, and the less power you waste. You'll see that FET drivers, like the TC4426 advertise that they can drive very high currents into the gates.
The high side FET on an H-Bridge needs a high voltage to switch it off. This is almost always too high for a normal logic circuit to interface to. The driver may also act as a voltage level converter.
Rocketmagnet
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Hi, did you means that the mosfet gate need high voltage in order to turn on the mosfet as well? What is the different in High and Low side of MOSFET? Why there will having a high and low side ? Is there any affect ? – sean900911 Feb 22 '13 at 00:38