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Old 20th April 2007, 06:28 AM   #1
Pierre is offline Pierre  France
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Default IR21xx + mosfet drivers

Hello.

I am planning to make a Class D output stage using big mosfets, TO247 devices with around 4000pF gate capacitance and 120nC gate charge. I plan to switch at around 350KHz, needing less than 100ns rise/fall times.

To swith such mosfets that fast, I need a mosfet driver after the IR2113 in order to upply much more current to the gates. My plan is to add a TC4420 (6 amps) or similar at the output of the high side and another one at the output of the low side. Has anyone tried this approach?
I have seen some schematics (Crest LT and others) using similar mosfets driven directly by the IR2113 with 39ohm resistors, but I guess that can't switch too fast at that frequency (perhaps they run at 100KHz or so?)

The supply of the lower one is straight forward, just -VSS + 12V.
The supply for the upper one is the bootstrap voltage, referenced to the switching point between mosfets. But... I suppose I need a large bootstrap cap.

What is a recommended starting value for the gate resistor (I use antiparallel diode as well)?

Thanks!
 
Old 20th April 2007, 11:06 AM   #2
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Default Re: IR21xx + mosfet drivers

Quote:
Originally posted by Pierre
Hello.

I am planning to make a Class D output stage using big mosfets, TO247 devices with around 4000pF gate capacitance and 120nC gate charge. I plan to switch at around 350KHz, needing less than 100ns rise/fall times.

To swith such mosfets that fast, I need a mosfet driver after the IR2113 in order to upply much more current to the gates. My plan is to add a TC4420 (6 amps) or similar at the output of the high side and another one at the output of the low side. Has anyone tried this approach?
I have seen some schematics (Crest LT and others) using similar mosfets driven directly by the IR2113 with 39ohm resistors, but I guess that can't switch too fast at that frequency (perhaps they run at 100KHz or so?)

The supply of the lower one is straight forward, just -VSS + 12V.
The supply for the upper one is the bootstrap voltage, referenced to the switching point between mosfets. But... I suppose I need a large bootstrap cap.

What is a recommended starting value for the gate resistor (I use antiparallel diode as well)?

Thanks!
Crest Audio LT1800 & CD3000 Runs at 250KHZ!

I have used 4 X IRFP460N with Rg=4.6Ohms,Series Schottky's MBR4045, HFA series FREDs, 2 X MIC4420 Gate Driver per side, Isolated +-15V for both hi-side and low side gate drivers....Switching Frequency= 250KHZ, 6N137 optocouple to drive the gate drivers...Rails were at +- 180VDC..idle, Rise/Fall time less than 75nS
 
Old 20th April 2007, 11:10 AM   #3
Pierre is offline Pierre  France
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Thanks.
I would like to keep the IR2113 for the level shift, shutdown, etc, and only buffer its outputs, using two TC- (or MIC-) 4420.
 
Old 20th April 2007, 11:32 AM   #4
alfsch is offline alfsch  Germany
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hmmm...
2A in 4nf gives about 20ns rise time, seems ok.

i would try 10 ohm + pnp for closing gate

my favorite pnp: zetex fmmt717 , 10A peak !!
that should close every mosfet :-)
 
Old 20th April 2007, 11:44 AM   #5
Pierre is offline Pierre  France
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Yes, but that will overheat the IR2113.
Now, with a IR2110 (SMD versio) and 3nF mosfets, it gets quite hot.
Mmmm. Have to try...

On my currently working-well circuit, I have tried the modification:
Added two TC4420's and 2.2ohm gate resistors, and the new mosfets, but there seems to be a lot of cross-conduction (the mosfets get quite hot even with no signal). Maybe two possible causes:

a) The bootstrap voltage is not enough and the upper mosfets gets into linear region. (I have used 100nF ceramic || 1 uF tantalum || 10uF tantalum from switching node to IR2110's VB (VCC of the upper TC4420). Not enough?

b) The dead time is not enough (before it was), or the mosfets are not turning off fast enough (I use an antiparallel diode, through it, the driver should turn it off strongly).


Any ideas?
 
Old 20th April 2007, 11:50 AM   #6
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Quote:
Originally posted by Pierre
Thanks.
I would like to keep the IR2113 for the level shift, shutdown, etc, and only buffer its outputs, using two TC- (or MIC-) 4420.

Then your Deadtime must be at least 180nS or more, if you want to avoid destruction of mosfets and also the Turn-OFF would be a problem, since you only have the option of reducing the Vgs during TURN-OFF to around Zero...which doesnot TURN-OFF the mosfet much faster...but In my case The availability of -5V VGS during TURN-OFF makes the mosfet to switch-off much faster and also deadtime is just 35nS....

Using IR2110/2113 along with Bootstrap supplies for driving High Capacitance Large Die High Voltage Mosfet isnot a good way..you would eventually end up with nothing but smokes and flames of different colors.....
 
Old 20th April 2007, 12:39 PM   #7
Pierre is offline Pierre  France
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Well, Crest LT does this way and they have fame of being very rudged and reliable...
 
Old 20th April 2007, 02:26 PM   #8
IVX is offline IVX  Russian Federation
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Pierre, maybe choice of the new mosfets much better idea vs raping heavy old ones? How much volts & amperes you need?
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Old 20th April 2007, 02:57 PM   #9
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Quote:
Originally posted by Pierre
Well, Crest LT does this way and they have fame of being very rudged and reliable...
Who told you this....LT series was discontinued since past 3 years just because there were reliability problems associated with them, only 230 units were produced out of which 89 were returned to factory just because of "HIGH FIELD FAILURE RATES", They were replaced by new CD3000...which is much more rugged and used robust techniques such as series schottkys and high side cascoded gate drive and also their LT series uses low gate charge APT single pair Mosfets...with rails voltage +-120V thats why IR2110 survived on their test bench but failed on field operation...

Quote:
Originally posted by IVX
Pierre, maybe choice of the new mosfets much better idea vs raping heavy old ones? How much volts & amperes you need?
IRFP460 is replaced by IRFP460N with improved features....less gate charge....but there are many more with much improved features from IXYS and Fairchild...
 
Old 20th April 2007, 03:35 PM   #10
IVX is offline IVX  Russian Federation
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IRFP460?? It's old hat from the other century, that's too far from current state of the semiconductors industry. I guess, that at moment Infineon is a leader at 400+ nomination, easyly to find the Infineon mosfet ~40nC with about ~100mOhm, i don't know if IXYS already can offer such one, but Fairchild can't (AFAIK).
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