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Old 16th December 2007, 04:46 PM   #31
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Is there any practical and easy way to see crossconduction on the scope without cutting any trace/inserting resistors?
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Old 17th December 2007, 05:37 AM   #32
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Quote:
Originally posted by lumanauw
Is there any practical and easy way to see crossconduction on the scope without cutting any trace/inserting resistors?
It is very very obvious if you look at gate-source signals or at the supply rails (provided that your circuit is clean enough so that you don't have 10 times stronger EMI on top of the interesting parts of the waveform).
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Old 17th December 2007, 05:50 AM   #33
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Hi, EVA,

is that Vgs 100% represent Ids?
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Old 17th December 2007, 07:27 AM   #34
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Talking of cross-conduction reduction: Has anyone ever tried Brian Attwood's output stage topology ?

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Old 17th December 2007, 07:35 AM   #35
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Quote:
Originally posted by lumanauw
Hi, EVA,

is that Vgs 100% represent Ids?
Vgs has the derivative of Ids summed during switching. Supply rails contain Ids too, multiplied by the impedance of the power supply system. This is advanced stuff, don't worry if you don't understand it at first, but it is very evident to te trained eye.
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Old 17th December 2007, 09:36 AM   #36
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Hi, Charles,

Quote:
Talking of cross-conduction reduction: Has anyone ever tried Brian Attwood's output stage topology ?
Where can I see it?

Hi, EVA,

I have to admit that my probing technique is not perfect yet for high frequencies. I still haven't implement AN-47 throughly yet. I still use standard probe. So, you can guess, sometimes it is confusing wheter one display is the real thing or probing mistake, in classD monitoring.

In my scope (100mhz digital), I can tilt one channel than add channel 1 and channel 2. When I do this for 2Vgs (top and bottom mosfets), I found out there are spikes.

I got gate picture similiar like this (JohnW's). How can I see if there is cross conduction from seeing only Vgs?
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Old 17th December 2007, 09:44 AM   #37
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Oh yes, EVA, all this time I monitor cross conduction by cutting traces, and then insert 2 resistors (1 resistor between upper source and output node, the second resistor between output node and lower drain). Then the output node is made the common for osciloscope and channel 1 and channel 2 both monitoring the other ends of the resistors. The resistor value is determined appropriate to the load and test signal until they both have about 1V drop. This way I can see cross conduction.
Is this technique good enough? I still want to find a technique to monitor cross conduction in classD (to adjust bias), but without cutting traces.
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Old 17th December 2007, 09:55 AM   #38
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David
Why Didn't you use current probes to check cross-conduction, its very easy!!!!
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Old 17th December 2007, 09:56 AM   #39
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I once thought about a method that measures cross-conduction the way David does by the use of small pulse transformers. The measured spikes could then be used for the automatic/adaptive setting of deadtime.

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Charles
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Old 17th December 2007, 10:15 AM   #40
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Quote:
Why Didn't you use current probes to check cross-conduction, its very easy!!!!
Hi, Kanwar,

How to do it?
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