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Old 27th April 2009, 04:15 PM   #1
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Default Lm391 N100

everybody has been arround this ic some times

havent touch any of them for years but out of the blue one amp that used it come in to the shop for repair .

while searching first for the ic it shelf ( it was blown beyond repair he he ) then i looked at the application which was the exact copy of the original application as given by national .....


then i noticed that eventhough i bias network exists to provide adjustable bias for the drivers and output there is no vbe multiplier ,,,,,,meaning that as amplifier warm probably bias will drift ....upwise as usual

any ideas ???? am i missing something ???
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Old 27th April 2009, 04:20 PM   #2
lms is offline lms  Micronesia
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vbe multiplier is in the LM391, which should be thermally coupled to the drivers for best bias stability
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Old 27th April 2009, 04:36 PM   #3
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Default thanks for your suggestion

but is something like that writen in the manual ????

if it is i missed it
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Old 27th April 2009, 05:40 PM   #4
mjf is offline mjf  Austria
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hello.
i looked at the datasheet of a lm 391 (www.datasheetcatalog.com).
vbe - biasing is built in...........and some other examples for user are shown.
greetings................
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Old 27th April 2009, 05:40 PM   #5
wg_ski is offline wg_ski  United States
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No , the data sheet didn't mention keeping the chip thermally coupled to the drivers. It just suggested a minimum value for Re which insured thermal loop stability (which does not necessarily mean zero drift).
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