MOSFET vs. MOSFET Driver??

Thread Starter

theeld

Joined Oct 5, 2006
12
Will someone tell me the difference between a MOSFET transistor and and MOSFET Driver??? Im looking for parts online and in some of the data sheets of a MOSFET Driver they use language similar to "They are capable of 6A (peak) output and can drive the largest MOSFETs with an improved safe operating margin."

what are they talking about "driving MOSFETS"?? as far as I know mosfets dont need alot of current at the gate since it is electrically isolated from the rest of the FET... does driving always mean "driving current" im confused... help

Theeld
 

beenthere

Joined Apr 20, 2004
15,819
Hi,

MOSFETs have specialzed drivers to help minimize turn-on and turn-off times. The advantage of very low on resistance is lost if the MOSFET takes a relatively long time going in and out of conduction. This will cause the device to heat up and fail, even though the circuit voltage and current were within the spec's of the MOSFET.

To the driver, a MOSFET's gate looks like a small capacitor. The driver places and removes charge from the gate in a big hurry (tens of nanoseconds).
 

Thread Starter

theeld

Joined Oct 5, 2006
12
So???

Can a MOSFET Driver be used in a similar situation as a regular MOSFET or is a MOSFET Driver supposed to be used in conjunction with a regular MOSFET??
 

Papabravo

Joined Feb 24, 2006
14,677
What part of "MOSFET drivers are used to minimize turn-on and turn-off times" do you not understand? No they cannot be used interchangeably. There is another small and often overlooked detail. MOSFET drivers can often create voltages to drive the gate to a higher voltage than the supply for the MOSFET. They do this with a so called "bootstrap" circuit. They do this so the rds(on) of the MOSFET is as small as possible.
 
Gate charge determines whether a MOSFET or IGBT is on or off. To the driver, the gate acts like a capacitor. The driver turns the transistor on or off in a matter of tens of nanoseconds, by charging or discharging the gate.

The MOSFET and Driver are like a Q and a U.
 

JMac3108

Joined Aug 16, 2010
348
Yes,the gate of a mosfet is high impedance and requires essentially zero DC current. BUT, the gate has capacitance that must be charged up when it is switched on, and discharged when it is switched off.

If you drive the gate of a mosfet with something that can not source much current (maybe a logic gate or micro-controller pin), it takes a while for the mosfet gate capacitance to charge up. During this time when the gate is charging up, the mosfet is partially on, operating in its linear region, and dissipating power. This will waste power and is inefficient, and in some cases could damage the mosfet.

The solution in situations where its important to turn on a mosfet quickly, is to use a mosfet gate driver that can source a lot of current to charge up the mosfet gate quickly.
 
Top