Continuing my work on a half bridge driver . I faced problem of slow Turn on/off of the mosfet due to the "relatively" low output current of the IR21844 mosfet driver (1.4A source and 1.8A sink).

Using the equation I=Q/ton . I found that for the total gate charge of 2500nC (5 mosfets in parallel) switched at 20khz , with the desired Ton 0.5us . I would need 5A.

Searching for a solution lead me to IR application note 978 containing this circuit

I was thinking if it can be simplified ( 4 transistors per output is too much space for me ) maybe something like using 1 TC4420 on each output (HO and LO) although this is not the purpose of this IC. I am also open for other methods or suggestions that doesnot involve changing the main gate driver.

thanks in advance !

 

I'm confused.
You initially talk about 5 MOSFETs in parallel, and then say you don't have room for 4 transistors per output.
So which is it?

 

Sorry for the confusion. In the circuit i posted above there is the IGBT module , this IGBT module in my case is 5 mosfets in parallel on a separate board. The 4 transistors i donot have room for are the ones added to boost the output current (2 x IRFD9110 and 2x IRFD110) which should be placed between the gate driver and the "IGBT module" . My question is that can i replaced those 4 transistors with 1 IC ?

 

Youre saying you now have 5 mosfets in your design, and thats good but you need a driver with more power and the driver your looking into calls for 4 mosfets per output so you would then either have 9 or 13 mosfets witch is too much for you design. thats how i read it.

 

That App note circuit has me puzzled.
1) What's the supply voltage for the drains of the high-side FETs?
2) The right-hand IRFD110's have no drain connection, so are those FETs being used simply for their gate capacitance?

 

Sorry for the confusion. In the circuit i posted above there is the IGBT module , this IGBT module in my case is 5 mosfets in parallel on a separate board.

To me this quote is the defining part of your question. While a separate power board and logic board is alright to do, having the drivers on a separate board is something to avoid. The power devices, mosfet or IGBT and their drivers should be together on the same board. There should be less than one inch or 25mm distance between driver and the power device being used.

Also what is the value of the resistor being used between gate and driver?

 

That App note circuit has me puzzled.
1) What's the supply voltage for the drains of the high-side FETs?
2) The right-hand IRFD110's have no drain connection, so are those FETs being used simply for their gate capacitance?

1)The "IGBT module" is placed 10 cm away from the board , it is supplied by 48v . while the IRFD110 and IRFD9110 are supplied by 15v because their purpose is to drive the gate of the "IGBT module" not the LOAD
2) The right hand IRFD110 as i noticed too, donot have drain connection , but i think it is a printing mistake , the drain is connected to the source of the IRFD9110 as i imagine (totem pole). these are used because they have low gate capacitance and can switch very fast to provide current higher than the driver can provide.