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 Posted: Feb 29, 2012 - 05:41 PM |
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Joined: Sep 20, 2003
Posts: 4061
Location: Surrey, England
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After much searching, it seems that I am unlikely to find a solution.
BJTs have too much collector/emitter voltage drop, and FETs require too much gate source voltage.
Even using an NPN BJT and a P FET is a problem, since I can only guarantee 2V6 to 3V? supply.
I thought about have the AVR go into power down mode, and be woken up by the mic bias voltage, but I can't be sure that, with a new coin cell, the mic bias will be high enough.
So I think what I will try is to feed the mic bias voltage into a BJT, take the collector to an AVR pin with a pullup(probably the internal one) and use that to wake the AVR. I suppose I could disable pullup after I'd woken up, and then re-enable at intervals to check if I'm still plugged in, but it's probably not worth the bother.
Now I need to check what sort of leakage there might be through the BJT collector/emitter.
Would that work, or am I missing something?
John |
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Posted: Feb 29, 2012 - 06:16 PM |
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Joined: Sep 20, 2003
Posts: 4061
Location: Surrey, England
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Posted: Feb 29, 2012 - 10:17 PM |
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Joined: Oct 20, 2005
Posts: 257
Location: Colorado
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Posted: Feb 29, 2012 - 10:25 PM |
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Joined: Jan 09, 2007
Posts: 1857
Location: Arlington, Texas, U.S.A.
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John_A_Brown wrote:
Hmmmm. Just found this: ... ZUMT618 ...
Thanks for the Zetex ZUMT618; I was not aware of these Zetex/Diodes parts. Simulates better than OnSemi NSS12201. The advantage of the high current gain (hfe) AND low Vce-sat bipolar transistors is the reduced base current for a given collector current and Vce. |
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Posted: Feb 29, 2012 - 10:32 PM |
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Joined: Jan 09, 2007
Posts: 1857
Location: Arlington, Texas, U.S.A.
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John_A_Brown wrote:
Now I need to check what sort of leakage there might be through the BJT collector/emitter.
Almost always very low IF base current is correctly controlled; FET's d-s leakage can be a problem especially at elevated temperatures. |
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