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Kain

IGBT and MOSFET drivers???

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Hi Kain,
A Mosfet driver chip is used to provide enough current to charge and discharge quickly the high capacitance of the gate of a Mosfet and its Miller Effect. It also has "dead time" to make sure that one Mosfet is turned off when the one connected to it turns on.

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Thanks Audioguru! Can you schematically show what you mean by saying that one MOSFET is connected to the other? I thought that they need to be both "on" if they are to conduct the current through the motor

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Hi Kain,
In your circuit, Mosfet Z1 is connected to Mosfet Z2. One transistor must be on and the other must be off. Similarily with Mosfet Z3 and Z4.

It takes time for the control signal to change, since it is a voltage ramp. Therefore there will be a moment when the Mosfets connected together are both turned on shorting the supply if there isn't any "dead time" when they are both off.

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Ok, so what you meant is that the driver chip is switching on and off the IGBT/MOSFET more efficiently as well as providing for "dead time" when reversing directions. Would you recommend any IC in your experience? Thanks again  ;D

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...the driver chip is switching on and off the IGBT/MOSFET more efficiently

This is also important if the motor draws a high current and it is pulsed at a high frequency for PWM speed control.

Would you recommend any IC in your experience?

Sorry, I have never made an H-bridge. IC drivers for them have been discussed on these forums.

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There are a few other clever parts to some driver chips.
A few models supply a built in PWM generator.

I like the HIP4080A for the projects I have worked on.
It has a feed back loop analogue mode that generates the PWM onboard based on a
voltage input target.  Although I have found that mode a bit tricky to use.

I prefer to use it in a digital mode where I can feed it a direction and PWM signal and
the chip handles all the rest.  The most valuable part of the chip is a charge pump that
creates the high voltage needed to trigger the MosFets (N-Channel) at the top of the bridge as they need to see slightly more than the source voltage. The charge pumps on the chip create a little more than the input voltage

Here is a link to a typical datasheet for this chip :  http://www.intersil.com/data/an/an9404.pdf

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