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Old 6th November 2012, 02:03 PM   #1
Einric is offline Einric  United States
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Default IRFP240 & 9240 Gate Source Breakdown Voltage

I am putting together parts for my F4 build.
Do I need the +-30V or will the +-20V be sufficient?
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Old 6th November 2012, 04:31 PM   #2
flg is offline flg  United States
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+- 20 - +-30V what? V breakdown at the gate??? Use the typical protection diodes scheme(Less than 20V). Or as ZM would say, show us a schematic???
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Old 6th November 2012, 04:37 PM   #3
Einric is offline Einric  United States
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Looking through Digikey they show the obsolete 240 & 9240 have GSBV of +-30V.
The current production Vishay 240 &9240 show GSBV of +-20V but are otherwise specd' the same.
This will be for application in a Pass F4 does it really matter with this circuit?

Last edited by Einric; 6th November 2012 at 04:51 PM.
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Old 6th November 2012, 05:06 PM   #4
flg is offline flg  United States
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There is a D1 and 2 in the pass F4 schematic. It originally had a 2N number for the protection diodes. That should be a 1N part number...
The above mentioned diodes prevent any input to the FET gate greater than the diode value. I don't honestly remeber the value but anything 10-15V should be fine.
Sinse Vishay bought the IR line, process, equip, and all, I would suppose the originall Vgs max is the same as it always was? (20V). Not 30V! that is likely a mistake. However, irrelavant. Any more than a few V above the necessay signal level is a waste. We are not trying to get low on resistance here.
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Old 6th November 2012, 06:01 PM   #5
Einric is offline Einric  United States
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Thank You
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Old 7th November 2012, 11:58 AM   #6
AndrewT is offline AndrewT  Scotland
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stick in the gate voltage protection.
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Old 7th November 2012, 12:04 PM   #7
Einric is offline Einric  United States
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Andrew, what do you mean?
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Old 7th November 2012, 12:18 PM   #8
AndrewT is offline AndrewT  Scotland
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Every competently designed mosFET output amplifier, I have ever seen, has gate voltage protection fitted.

Once that is fitted, Vgs limitations do not ever become transgressed.
Quote:
stick in the gate voltage protection.
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Old 7th November 2012, 12:33 PM   #9
Einric is offline Einric  United States
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So that is what the 6.8V Zener is for.
So I should have no problem with the +-20V.
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Old 7th November 2012, 04:46 PM   #10
flg is offline flg  United States
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Well, it sounds like you understand. And there are a few making the same question recently on other threads???. The zeners in the schemo are there to protect excessive high (>20V) Vgs from burning a hole in the oxide between the Gate metal (gate connection) and the channel(source in this dicussion). Once you burn a little hole in that oxide, the MOSFET is not what you think it is anymore, and is likely a permanant short! The first and formost protection Andrew is suggesting is likely correct. Just don't blow off those G-S diodes unless you know what your doing. less than 20V is a good Idea but more than 5V is probably also good. I like a 14V zener '-) Arguably, the next most important parameter is how hot those suckers are? How much bias you set it up for? Hotter is better to a point. The point where you've lost control and you melt the channel...
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