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Old 6th April 2005, 04:25 AM   #1
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Default A42 in Threshold amp

In some Threshold amp, I found configuration like this for A42. Base and collector are tied together, but the emitors are more positive than the base/collector.

What is the name of using this transistor like this? How many mA will pass in this configuration?
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File Type: jpg a42.jpg (4.6 KB, 276 views)
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Old 6th April 2005, 01:36 PM   #2
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Hi, Walter Burkhart

Indeed it makes a dioda if the collector/base is more positive than the emitor. But in here, the emitors are more positive, like inversed diode.
What happened to a transistor treated this way?
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Old 6th April 2005, 09:04 PM   #3
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It's a zener diode, at about 7 volts, which is a typical
E-B breakdown voltage. Check to make sure though,
as some bipolar fab processes yield different voltages.
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Old 6th April 2005, 09:07 PM   #4
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Interesting, but why not use a simple zener?

/Hugo
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Old 6th April 2005, 09:22 PM   #5
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Just to be bad and confuse everybody.

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Old 6th April 2005, 09:30 PM   #6
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No doubt I believe you, you sometimes do have that tendency which we all like I presume.
Only from a commercial point of view, two transistors are more expensive than a zener. Well, for mass consumer products that would be the consideration.

/Hugo
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Old 7th April 2005, 03:54 AM   #7
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Quote:
Just to be bad and confuse everybody.
I've noticed this for quite some time, but since the .jpg is kind of blurry, I think it is a misdirected arrow. But once I got another sch that uses this, and the arrow and the marking A42 is clear, I know, I haven't recognize this kind of transistor usage.

Does everyone here knows this except me?
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Old 7th April 2005, 07:38 PM   #8
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Quote:
Originally posted by Netlist
Only from a commercial point of view, two transistors are more expensive than a zener. Well, for mass consumer products that would be the consideration./Hugo
Depends on whether you have large boxes of A42's that fall out
of the selection process.

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Old 7th April 2005, 07:40 PM   #9
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Something else you might not know is that the typical
bipolar transistor works backward (exhange C for E)
but not a rated voltage - The BE breakdown voltage is
the limit.
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Old 7th April 2005, 09:33 PM   #10
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That pretty much answers the question in post #2.
But what are A42's? I did find 2SA42 but that's an old germanium...and PNP

/Hugo
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