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How to match Mosfet Gate Driver with Mosfet
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ZeroResistance:
I currently have a mosfet gate driver (half bridge) IR2111.
Max output current is 200mA, min rise time is 80nS, max is 130nS
I want to drive a IRF540 mosfet with this and turn it on as fast as I reasonably can, the faster the better. The Qg (total gate charge) of this mosfet is 71nC.
By using I = Qg/ t, and using t as 80nS we get  a current of 0.9A which is more than four times than that of the gate driver. I could of course choose a higher current rated gate driver however currently I only have this in my kitty.
How do I ensure that I do drive the mosfet as fast as I can and yet stay within the limits of the gate drivers max output current?
Is it as simple as adding a series gate resistor at the IRF540 gate?
T3sl4co1l:
Are you sure you actually want to turn it on "as fast as possible"?

Many things, probably far more extreme that you are expecting, are possible.  Particularly given enough budget.  A woefully underconstrained problem like "as fast as possible" leads to very interesting, but not ultimately very helpful, proposals. :)

If you're worried about the driver itself, it is fine to connect to a minimal resistance load.  Read the datasheet, it's measured with -- I forget what for IR2111 exactly, but 1nF or 10nF load, no resistance, is very common.

BTW, the equivalent gate capacitance is Qg / Vgs(on), or about 7nF here.

Tim
jmelson:

--- Quote from: ZeroResistance on August 28, 2018, 06:36:20 pm ---I currently have a mosfet gate driver (half bridge) IR2111.
Max output current is 200mA, min rise time is 80nS, max is 130nS
I want to drive a IRF540 mosfet with this and turn it on as fast as I reasonably can, the faster the better. The Qg (total gate charge) of this mosfet is 71nC.
By using I = Qg/ t, and using t as 80nS we get  a current of 0.9A which is more than four times than that of the gate driver. I could of course choose a higher current rated gate driver however currently I only have this in my kitty.
How do I ensure that I do drive the mosfet as fast as I can and yet stay within the limits of the gate drivers max output current?
Is it as simple as adding a series gate resistor at the IRF540 gate?

--- End quote ---
If you want fast, you need a stronger gate driver.  I think IR has up to about 6 A capability.  200 mA is really weak, and will lead to long turn-on and turn-off times, causing extra heating in the transistors.  I use the IR2113 (6A) and the IR2181 (I think) at 2 A.

Jon
ZeroResistance:

--- Quote from: T3sl4co1l on August 28, 2018, 06:38:45 pm ---Are you sure you actually want to turn it on "as fast as possible"?

Many things, probably far more extreme that you are expecting, are possible.  Particularly given enough budget.  A woefully underconstrained problem like "as fast as possible" leads to very interesting, but not ultimately very helpful, proposals. :)

If you're worried about the driver itself, it is fine to connect to a minimal resistance load.  Read the datasheet, it's measured with -- I forget what for IR2111 exactly, but 1nF or 10nF load, no resistance, is very common.

BTW, the equivalent gate capacitance is Qg / Vgs(on), or about 7nF here.

Tim

--- End quote ---

OK so maybe I worded it wrongly, however I checked the datasheet and saw that the rise time of the IRF540N is around 35nS @ 50V /16A with a gate resistor of 5 ohm.
BTW I do f ind a  CL = 1000pF mentioned in the IR2111 datasheet.
ZeroResistance:

--- Quote from: jmelson on August 28, 2018, 06:48:44 pm ---
--- Quote from: ZeroResistance on August 28, 2018, 06:36:20 pm ---I currently have a mosfet gate driver (half bridge) IR2111.
Max output current is 200mA, min rise time is 80nS, max is 130nS
I want to drive a IRF540 mosfet with this and turn it on as fast as I reasonably can, the faster the better. The Qg (total gate charge) of this mosfet is 71nC.
By using I = Qg/ t, and using t as 80nS we get  a current of 0.9A which is more than four times than that of the gate driver. I could of course choose a higher current rated gate driver however currently I only have this in my kitty.
How do I ensure that I do drive the mosfet as fast as I can and yet stay within the limits of the gate drivers max output current?
Is it as simple as adding a series gate resistor at the IRF540 gate?

--- End quote ---
If you want fast, you need a stronger gate driver.  I think IR has up to about 6 A capability.  200 mA is really weak, and will lead to long turn-on and turn-off times, causing extra heating in the transistors.  I use the IR2113 (6A) and the IR2181 (I think) at 2 A.

Jon

--- End quote ---
I will move to a faster driver as soon as I can but for my immediate tests I need to get this driver working. My frequency of turning on is not too high here maybe just a momentary pulse so I'm not so concerned about the heating.
I just don't want to damage the gate driver, so how do I ensure that the current is within the 200mA limit and how much turn on time should I expect in the mosfet.
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