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When to use a MOSFET driver?

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shadewind:
Hi,

I'm planning to dim lots of LEDs with MOSFETs and I've been looking at these:
http://www.irf.com/product-info/datasheets/data/irfh7914pbf.pdf

I've designed a board which uses a Microchip MOSFET driver but I see now that I could probably drive it directly with the MCU by looking at Fig 7 on page 4. What are the disadvantages of doing so in this case? From what I've learned, this would lead to a slower switching time since the MCU cannot deliver as much current and also higher on resistance since the MCU only gives out 3.3V as opposed to the MOSFET driver which I drive with 12V. Would you use a driver in this case?

jackbob:
What you linked is just a volatage converter it won't do the job your looking to do. I believe you are trying to drive mosfets with microcontroller using pwm. In this case yes use a tc4422 fet driver they work great.

Jacob.

shadewind:

--- Quote from: jackbob on October 15, 2011, 09:20:09 pm ---What you linked is just a volatage converter it won't do the job your looking to do. I believe you are trying to drive mosfets with microcontroller using pwm. In this case yes use a tc4422 fet driver they work great.

Jacob.

--- End quote ---
No I'm pretty sure I linked to IRFH7914PbF which is a power MOSFET from International Rectifier. And yes, I'm sure the Microchip FET drivers work great. That was not my question though.

mikeselectricstuff:
Bottom line is you need a driver when you want to switch big mosfets fast, as the gates have significant capacitance.
The driver (a)  supplies the high pulse current to charge & discharge  the gate quickly to keep it out of the partly-conducting state for any length of time to maximise switching efficiency, and (b) increases the drive voltage from logic level to a higher voltage (typically 5-15v) to turn the fet on as hard as possible to minimise static losses. 
If you're just turning LEDs on, or PWMing at a few hundred Hz, chances are you don't need a seperate driver unless you're up in the tens of amps range.

shadewind:

--- Quote from: mikeselectricstuff on October 15, 2011, 10:43:12 pm ---Bottom line is you need a driver when you want to switch big mosfets fast, as the gates have significant capacitance.
The driver (a)  supplies the high pulse current to charge & discharge  the gate quickly to keep it out of the partly-conducting state for any length of time to maximise switching efficiency, and (b) increases the drive voltage from logic level to a higher voltage (typically 5-15v) to turn the fet on as hard as possible to minimise static losses. 
If you're just turning LEDs on, or PWMing at a few hundred Hz, chances are you don't need a seperate driver unless you're up in the tens of amps range.

--- End quote ---
Right, so in this case it probably won't matter? I'm assuming this MOSFET doesn't qualify as "big"? But I'm thinking I might as well use a driver anyway to learn new things. It also means that the board can be driven at higher frequencies/currents and by arbitrary sources if I should ever want to.

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