Driving large mosfets: active PNP turn off

Pierre · 28th May 2007, 10:03 AM

What characteristics should I look for the PNP transistor in an active PNP turn-off circuit for driving large TO247 mosfets? It is intended to be after the IR211x driver output.

-I guess VCEmax around 25V is more than enough, as Vce=Vgs.
-A high max. collector current (2 to 10 amps) is desired for really fast turn off, right?
-What about Hfe min, transition frequency, etc?

I want to run it at 350KHz approx.

I have found some candidates such as :

MJD2955
ZXTP2012ZTA
MJD45H11TM

Do you think they are suitable? Would you recommend any other part number?

Thanks!

alfsch · 28th May 2007, 10:56 AM

my favorite:
zetex fmmt717 , 10 A peak !!!! , sot23 , hfe > 200, 110Mhz

The Saint · 28th May 2007, 11:07 AM

Don't the IR211x gate driver IC already have active gate turn off?

Also they can switch at 120ns..???

fredos · 28th May 2007, 02:42 PM

A 2n3906 is enought! The peak to discharge a gate is about fews ns....Except if you use a tick trace on your PCB, IR2110 is enought to discharge it. The only draw back, is the dissipation. Here you need a PNP discharge help...

Fred

Pierre · 28th May 2007, 03:13 PM

Well, I have seen some peak before turning on in the Vgs voltage that I don't like, it grows (up to 6-7V or more) as duty cycle is increased. I believe it can be due to reverse transfer capacitance turn on, so I think that a PNP turn off will help keeping the Vgs voltage down. Right?
I also want my IR2110 working more relaxed...

odnaizutra · 29th May 2007, 04:57 PM

if you change the gate driver to ir2010 isnt easier?

Gyula · 30th May 2007, 11:52 PM

Hi! Why don't you use TC4422 and ADuM isolator close to GS for a few ns?

Pierre · 31st May 2007, 10:39 AM

Well, about IR2010, nice, but "only" 200V max. Vcc. A bit tight if you want +/-90V rails, isn't it?
Adding an optoisolator (or similar) and mosfet driver is a good idea, but I want to keep it as similar to the original design as possible, by the moment (using only IR2110).

IVX · 31st May 2007, 12:09 PM

Follower using it's good idea indeed, ir2110 almost have not chance to live, after the mosfet blew up, bc807/817 will have much more chance even. On the other hand, why you need 2A($2) driver, if followers in use anyway? So, you can get more reliability for less money.

Pierre · 31st May 2007, 01:00 PM

The idea is simply to update the existing design for faster turn-off, by the use of a typical active-turn off PNP transistor.
The turn-on is still driven by the IR2110, so you need 2A. This way the chip will work more relaxed, too, as it doesn't have to sink the high turn off current.

28th May 2007, 10:03 AM	#1
Pierre Banned Join Date: Nov 2004 Location: Paris	Driving large mosfets: active PNP turn off What characteristics should I look for the PNP transistor in an active PNP turn-off circuit for driving large TO247 mosfets? It is intended to be after the IR211x driver output. -I guess VCEmax around 25V is more than enough, as Vce=Vgs. -A high max. collector current (2 to 10 amps) is desired for really fast turn off, right? -What about Hfe min, transition frequency, etc? I want to run it at 350KHz approx. I have found some candidates such as : MJD2955 ZXTP2012ZTA MJD45H11TM Do you think they are suitable? Would you recommend any other part number? Thanks!

31st May 2007, 12:09 PM	#9
IVX diyAudio Member Join Date: Jul 2003 Location: Everywhere (Buddhist's context)	Follower using it's good idea indeed, ir2110 almost have not chance to live, after the mosfet blew up, bc807/817 will have much more chance even. On the other hand, why you need 2A($2) driver, if followers in use anyway? So, you can get more reliability for less money. __________________ Best regards, E1.

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28th May 2007, 10:56 AM	#2
alfsch diyAudio Member Join Date: Jan 2002 Location: augsburg	my favorite: zetex fmmt717 , 10 A peak !!!! , sot23 , hfe > 200, 110Mhz

28th May 2007, 11:07 AM	#3
The Saint diyAudio Member Join Date: Jul 2002 Location: Launceston, TAS, Australia	Don't the IR211x gate driver IC already have active gate turn off? Also they can switch at 120ns..???

28th May 2007, 02:42 PM	#4
fredos diyAudio Member Join Date: Mar 2005 Location: Quebec	A 2n3906 is enought! The peak to discharge a gate is about fews ns....Except if you use a tick trace on your PCB, IR2110 is enought to discharge it. The only draw back, is the dissipation. Here you need a PNP discharge help... Fred

28th May 2007, 03:13 PM	#5
Pierre Banned Join Date: Nov 2004 Location: Paris	Well, I have seen some peak before turning on in the Vgs voltage that I don't like, it grows (up to 6-7V or more) as duty cycle is increased. I believe it can be due to reverse transfer capacitance turn on, so I think that a PNP turn off will help keeping the Vgs voltage down. Right? I also want my IR2110 working more relaxed...

29th May 2007, 04:57 PM	#6
odnaizutra diyAudio Member Join Date: Jan 2007	if you change the gate driver to ir2010 isnt easier?

30th May 2007, 11:52 PM	#7
Gyula diyAudio Member Join Date: Feb 2004 Location: Kunszentmárton, Hungary	Hi! Why don't you use TC4422 and ADuM isolator close to GS for a few ns?

31st May 2007, 10:39 AM	#8
Pierre Banned Join Date: Nov 2004 Location: Paris	Well, about IR2010, nice, but "only" 200V max. Vcc. A bit tight if you want +/-90V rails, isn't it? Adding an optoisolator (or similar) and mosfet driver is a good idea, but I want to keep it as similar to the original design as possible, by the moment (using only IR2110).

31st May 2007, 01:00 PM	#10
Pierre Banned Join Date: Nov 2004 Location: Paris	The idea is simply to update the existing design for faster turn-off, by the use of a typical active-turn off PNP transistor. The turn-on is still driven by the IR2110, so you need 2A. This way the chip will work more relaxed, too, as it doesn't have to sink the high turn off current.

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