EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: alireza7 on September 22, 2017, 07:56:19 pm
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hi
as you know gate of mosfets approximately source/sink zero current and it seems very easy to drive, so why these special mosfet gate driver ics exists ?
what is the advantages of using a mosfet gate driver ic?
is it crucial to use a mosfet gate driver ic instead of simply drive the gate by a microcontroller i/o?
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Power MOSFETs have very high gate resistance, yes, but also quite high gate capacitance (in the nF range). If you want to turn them on or off quickly, you need a driver that can handle this.
If you just want to turn on a lamp, the I/O pin from an MCU is fine for gate drive.
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Based on your circuit, you may also need the gate driver to boost voltage. The most common example of that is when you are using an N-channel mosfet to source current to a load (i.e., the load is connected to ground and the mosfet source is connected to the load). In that case, you need to boost the gate voltage to greater than the supply voltage.
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Based on your circuit, you may also need the gate driver to boost voltage. The most common example of that is when you are using an N-channel mosfet to source current to a load (i.e., the load is connected to ground and the mosfet source is connected to the load). In that case, you need to boost the gate voltage to greater than the supply voltage.
i saw this topology and i always wondering why don't they just use a p channel mosfet in this case ( when one side of the load is connected to ground and mosfet connects the other side to vcc)
It wouldn't be better to use a p channel mosfet in this case ? is there an special reason that i don't know for using this topology?
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Most Mosfets need at least 10V from gate to source to fully turn on. The 5V from a microcontroller will barely turn on most ordinary Mosfets.
To drive a Mosfet with a 5V microcontroller then use a "logic level" mosfet.
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Based on your circuit, you may also need the gate driver to boost voltage. The most common example of that is when you are using an N-channel mosfet to source current to a load (i.e., the load is connected to ground and the mosfet source is connected to the load). In that case, you need to boost the gate voltage to greater than the supply voltage.
i saw this topology and i always wondering why don't they just use a p channel mosfet in this case ( when one side of the load is connected to ground and mosfet connects the other side to vcc)
It wouldn't be better to use a p channel mosfet in this case ? is there an special reason that i don't know for using this topology?
Yes, the special reason is the theoretical MOSFET vs the reallife MOSFET :).
Reallife PFETS are harder to produce than there NFET counterparts so there are lees types to choose from, they have a higher price and there NFET counterparts are better specced.
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Because sometimes you need to switch on and off that MOSFET at 100KHz. And the rise and fall time has to be as small as possible, because that will lead to losses. So you need to charge the gate as fast as possible, to some 6-12V. A small FET has a gate resistance of some 10 Ohm. If you connect 10V through a 10 Ohm resistor into a capacitor, you get 1A peak for a short time. And that is why you need a FET driver.
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Regarding MOSFETs and, particularly, their Gate drive quirks, here you are (https://www.eevblog.com/forum/beginners/how-transistors-work/msg109559/#msg109559)!
-George
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Reallife PFETS are harder to produce than there NFET counterparts so there are lees types to choose from, they have a higher price and there NFET counterparts are better specced.
It has to do with charge carrier mobility in the channel. Electrons (charge carriers of N-channel FETs) have triple the mobility of holes (charge carriers of P-channel FETs) in crystalline silicon.
Making a P-ch FET that conducts as well as its N-ch counterpart would mean making it tree times as wide, with all the negative side effects (higher parasitic capacitance and thus reduced speed).