How to minimise crossconduction

ionutgaga · 9th December 2007, 03:34 PM

I have too much deadtime in my prototype (6n137@1kohm+tc429cpa+10ohm+irfp260n). Minimum deadtime is from 74hc02+1kohm+390p+1n4148. Trying to reduce, i have too much cross-conduction.

ajazz · 9th December 2007, 04:01 PM

No help without a schematic?

ionutgaga · 9th December 2007, 04:13 PM

Is very simple to find out what topology i'm using; look out my photo and my description... half bridge

ajazz · 9th December 2007, 05:12 PM

I knew it's ur standard half bridge, but still can't help much without knowing the Frq, mosfets and drivers used.

The 1K & 390p already seems too much for a Dt above 75K Frq as per my experience. But still the Cross conduction problem what you experience can be because of slow mosfets with high Qgd & high Trr or small gate resistors or can be any other reason which can be only identified by knowing your circuit. Even ur circuit layout matters.

A lot many schematics has already been discussed in the forum from which u can easily solve ur problem.

Eva · 9th December 2007, 06:35 PM

Do you experience cross-conduction when the amplifier is idle too or only with some signal and load?

Bear in mind that IRFP260N is very old and is absolute junk for class-D due to the hyper-slow body diode and the ultra-high gate charge, you need newer generation MOSFETs, preferably in TO-220 case.

ionutgaga · 9th December 2007, 06:45 PM

I have a couple of IRFP260N; i know that is a junk, but i have seen a comercial classD amp that it use this. I have crossconduction at idle, resistive 4ohm load. And small hiss...
Do you think that my inductor (gapped 2mm 3f3 toroid ferite) is the source of my problem? Or IRFP260N only?
What low cost 40-50a/200v device do you recomand me?

ionutgaga · 10th December 2007, 05:31 PM

Partial resolved with add of schottky diode paralel to Rg=10 ohm. Now, the deadtime is formed with 1k and 100p. Remember, with IRFP260N, Fsw=250khz. Plays stable with 1 ohm output and +/-90v...

Workhorse · 11th December 2007, 11:41 AM

Quote:

Originally posted by ionutgaga
Partial resolved with add of schottky diode paralel to Rg=10 ohm. Now, the deadtime is formed with 1k and 100p. Remember, with IRFP260N, Fsw=250khz. Plays stable with 1 ohm output and +/-90v...

Bypass the body diode

Workhorse · 11th December 2007, 11:44 AM

Quote:

Originally posted by ajazz
No help without a schematic?

ajazz · 11th December 2007, 07:51 PM

My Dear Kanwar,

I thought of solving all his problems in one go instead of giving him step by step instructions.
Like for instance first he created a dead time by adding a diode at the gate and then you suggested to bypass the body diode and now there can be many other problems to create a perfect Damp.

By asking for his schematics we(all other experts) could have solved his problem in one shot.

Today there is nothing great in designing a Half-Bridge circuit using self oscillation or synchronised version as there are umpteen number of circuits available('cos it's the first step Damp) and people are still toying around the same.

I would appreciate some different & better topologies to be discussed on this forum like DIY BCA or Phase Modulated etc etc.

May be I will have to start one shortly.

9th December 2007, 04:01 PM	#2
ajazz diyAudio Member Join Date: Apr 2005 Location: INDIA	What's ur topology No help without a schematic?

9th December 2007, 06:35 PM	#5
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	Do you experience cross-conduction when the amplifier is idle too or only with some signal and load? Bear in mind that IRFP260N is very old and is absolute junk for class-D due to the hyper-slow body diode and the ultra-high gate charge, you need newer generation MOSFETs, preferably in TO-220 case. __________________ I use to feel like the small child in The Emperor's New Clothes tale

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9th December 2007, 04:13 PM	#3
ionutgaga diyAudio Member Join Date: Jul 2006	Is very simple to find out what topology i'm using; look out my photo and my description... half bridge

9th December 2007, 05:12 PM	#4
ajazz diyAudio Member Join Date: Apr 2005 Location: INDIA	I knew it's ur standard half bridge, but still can't help much without knowing the Frq, mosfets and drivers used. The 1K & 390p already seems too much for a Dt above 75K Frq as per my experience. But still the Cross conduction problem what you experience can be because of slow mosfets with high Qgd & high Trr or small gate resistors or can be any other reason which can be only identified by knowing your circuit. Even ur circuit layout matters. A lot many schematics has already been discussed in the forum from which u can easily solve ur problem.

9th December 2007, 06:45 PM	#6
ionutgaga diyAudio Member Join Date: Jul 2006	I have a couple of IRFP260N; i know that is a junk, but i have seen a comercial classD amp that it use this. I have crossconduction at idle, resistive 4ohm load. And small hiss... Do you think that my inductor (gapped 2mm 3f3 toroid ferite) is the source of my problem? Or IRFP260N only? What low cost 40-50a/200v device do you recomand me?

10th December 2007, 05:31 PM	#7
ionutgaga diyAudio Member Join Date: Jul 2006	Partial resolved with add of schottky diode paralel to Rg=10 ohm. Now, the deadtime is formed with 1k and 100p. Remember, with IRFP260N, Fsw=250khz. Plays stable with 1 ohm output and +/-90v...

11th December 2007, 07:51 PM	#10
ajazz diyAudio Member Join Date: Apr 2005 Location: INDIA	My Dear Kanwar, I thought of solving all his problems in one go instead of giving him step by step instructions. Like for instance first he created a dead time by adding a diode at the gate and then you suggested to bypass the body diode and now there can be many other problems to create a perfect Damp. By asking for his schematics we(all other experts) could have solved his problem in one shot. Today there is nothing great in designing a Half-Bridge circuit using self oscillation or synchronised version as there are umpteen number of circuits available('cos it's the first step Damp) and people are still toying around the same. I would appreciate some different & better topologies to be discussed on this forum like DIY BCA or Phase Modulated etc etc. May be I will have to start one shortly.