What is Mosfet Driver?? How Does it work??

Discussion in 'General Electronics Chat' started by keathow87, Mar 5, 2011.

  1. keathow87

    Thread Starter New Member

    Feb 6, 2011
    1) Anyone please explain to me why we can't just drive the gate of the Mosfet by using DC voltage instead of using Mosfet driver??

    2) How does Mosfet driver work actually?

    3) What input should we give to the Mosfet driver to get the desired output?? Please explain using this Mosfet driver for example, if I want to have a 13.56MHz 15Vp output to be used for Mosfet switching http://www.farnell.com/datasheets/32537.pdf

    Thanks in advanced and your help are very needed and appreciated =)
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
    1) Unless you using a logic level mosfet, you need at least 10V to turn it completely on. The driver also gives more current to turn the mosfet on quicker, the faster a mosfet switches the lower the heat it produces.

    2) The driver internally switches the higher voltage/current, allowing the mosfet to switch faster. The gate of a mosfet is like a big capacitor(no connection is made to the drain and source in the mosfet) The faster you can 'charge' the gate(capacitor) the faster it will turn the mosfet on.

    3) You need to give a signal of 5V(square wave) to pin #2 at what ever frequency you want to switch your mosfet at. The other pins would be at the levels stated in the data sheet. Pins #6 OR #7 would go to the gate of your mosfet. You can only use one at a time, either a N mosfet on pin#6 OR a P mosfet on pin #7. You can't use both out puts at the same time.

    Here is an Application Note on the use of the driver; http://datasheet-found.com/Datasheet.jsp?pn=EL7104
    Last edited: Mar 5, 2011
  3. JMac3108

    Active Member

    Aug 16, 2010
    Shortbus is correct except for a minor detail...

    The gate of a MOSFET has a very small capacitance (in pf) but this is significant when you are trying to switch at a high speed. MOSFET drivers can source high currrents to quickly charge up this cap.

    If you are just using the MOSFET to switch a load on and off (maybe an LED or a relay) then a MOSFET driver is not required. Use a logic level MOSFET and drive it with your mico-controller or logic.
  4. Jaguarjoe

    Active Member

    Apr 7, 2010
    Most MOSFET datasheets list a value for gate charge in nC (Nanocoulombs). Shuffelling Q = CV and I = C(dv/dt), you get Q = I*T. You know Q, so now you can see how much "I" you need to switch the MOSFET in "T" seconds.
  5. keathow87

    Thread Starter New Member

    Feb 6, 2011
    thanks for all the explanation, now I have better understanding of it.

    By the way, can you guys help me determine if this op-amp connection correct?? From the circuit, usually op-amp need a bipolar supply which is +/-15V...but the problem is I don't have a bipolar supply and I don't want to use the single ended design, so in the end I plan to supply it with two independent DC power supply, both supplying 15V but I'll connect one of the 15V positive pin to ground and its negative pin to the op-amp for the purpose of -15V, will this work?? I wish to amplify the 13.56MHz 3Vp square wave signal to 15Vp using EL2045, is that possible?

    note: I'm not using it to switch the Mosfet but its another part needed in my project.