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Old 25th July 2012, 12:13 PM   #1
jeepy is offline jeepy  Switzerland
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Hello,
Could the 2sa970 and 2sc2240 replace the MPSL01 and MPSL51 even if their Hfe is higher? ..>200. (I have a reasonable stock of those). Output stages will use IRF130 and power rails = +/-41V.
Thanks,
jeepy
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Old 25th July 2012, 01:05 PM   #2
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by jeepy View Post
Hello,
Could the 2sa970 and 2sc2240 replace the MPSL01 and MPSL51 even if their Hfe is higher? ..>200. .....
irrelevant

look just at P , I , U of xsistors for substitution

Quote:
Originally Posted by jeepy View Post
....... Output stages will use IRF130 and power rails = +/-41V.
........
rails are somewhat high for those IRF's

be careful with that axe , Eugene ;

either :

- use lower rails,or
-use mosfets with higher voltage range,or
-be sure that you're not using full swing on output
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Old 26th July 2012, 10:57 AM   #3
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Quote:
Originally Posted by jeepy View Post
Hello,
Could the 2sa970 and 2sc2240 replace the MPSL01 and MPSL51 even if their Hfe is higher? ..>200.
Generally speaking, with an amp made from BJT's, its the circuit that sets the gain,
not the Beta (hFE) of the BJT.
But don't use a darlington where a singe BJT should be.

If you look at the datasheets, there are typically clues - like Noise Figure or maximizing hFE
of where its best to set the bias for that particular BJT.

As Zen pointed out, also make sure Vce(max) and P are well within the BJT's limits.

In this case, I'm wondering if the higher Beta will actually improve the CMRR
of the differential pair.
.
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Old 26th July 2012, 01:06 PM   #4
jeepy is offline jeepy  Switzerland
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Quote:
Originally Posted by Uunderhill View Post
Generally speaking, with an amp made from BJT's, its the circuit that sets the gain,
not the Beta (hFE) of the BJT.
But don't use a darlington where a singe BJT should be.

If you look at the datasheets, there are typically clues - like Noise Figure or maximizing hFE
of where its best to set the bias for that particular BJT.

As Zen pointed out, also make sure Vce(max) and P are well within the BJT's limits.

In this case, I'm wondering if the higher Beta will actually improve the CMRR
of the differential pair.
.
Thanks to you and Zen!
The 300mW PD may not be enough for the Vas and driver so I will use the 2N5551 instead. I will use the 2SA940 for the diff pair due to better noise figure and other specs in range.
Thanks again
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