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Old 18th May 2006, 12:08 PM   #1
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Default Output transistor substituting

Gidday ppl,

i was asked by another tech today about replacing a 2SB755 /2SD845 with 2SA1494/2SC3858

question is what are the effects of to low or high HFE in an output stage - this is unfamiliar territory for me as i mainly deal in Hybrid Power ICs

- Baily
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Old 18th May 2006, 12:22 PM   #2
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Too high hFE can result in instability but unless it's massively higher it's not usually a problem. Too low on the other hand and you cripple the driver stage (at the very least) and distortion goes up.
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Old 18th May 2006, 12:27 PM   #3
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The HFE of the 2SB/D ranges from 55-160 (from toshiba datasheet)

the 2SA/C ranges from 50-180 (from Sanken datasheet)
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Old 18th May 2006, 01:42 PM   #4
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Those are so close as I'm surprised your even asking really!

fT would be the parameter to watch if voltage and current, SOA are all similar, now you've ruled out hFE.
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Old 18th May 2006, 02:26 PM   #5
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Hi richie00boy,
100 % agree with you! On everything.

-Chris
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