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Old 16th June 2010, 03:24 PM   #1
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Default Biasing and cascoding questions

Hi Everybody,

I have some questions on good bias point for the 2SK170/J74 and IRF610/9610 and on cascoding device, if anybody has something to share, please go ahead.

1) My question on the low power jfet is:
is it correct to say looking at the datasheet that the most linear point/ vs power dissipation vs current input demands (if paralleled and used as input for low output cartridge) would be Id 5.5mA/ VDS 13V ?
And if so, the question is, is it better to select from the GR type the specifc current or having an higher IDSS one and put lets say a 18-22ohm feedback resistor?

2) the IRF610/9610 curve looks like that by increasing the current at the drain decreases linearity as the curve starts bending down steeper and steeper as Id goes up.
Would it 15mA be good bias point? also degeneration resistor, what is the ideal voltage drop across the resistor? for BJT the "magic number" is 25mV, what about MOS-Fets?

3) A last question on cascoding device: I am currently using 2SA1538/2SC3955 which are very good device, but here again the 1538 seems not to be so linear at higher current like 35-40mA.
Do you guys have a good cascoding device in mind that I might give a try to?

Best
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Old 18th June 2010, 02:07 PM   #2
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woohhhh!!what's going on with the DIY forum?
It seems like people are only interested on building somebody else's thing...but when it comes to discuss technical subjects it looks like there is no interest whatsoever.
Too bad, I thought it could have been an interesting subject, maybe not I guess.

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