I am putting together parts for my F4 build.
Do I need the +-30V or will the +-20V be sufficient?
Do I need the +-30V or will the +-20V be sufficient?
+- 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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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?
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?
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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.
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.
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.
Once that is fitted, Vgs limitations do not ever become transgressed.
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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