A42 in Threshold amp

lumanauw · 6th April 2005, 03:25 AM

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?

lumanauw · 6th April 2005, 12:36 PM

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?

Nelson Pass · 6th April 2005, 08:04 PM

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.

Netlist · 6th April 2005, 08:07 PM

Interesting, but why not use a simple zener?

/Hugo

Nelson Pass · 6th April 2005, 08:22 PM

Just to be bad and confuse everybody.

Netlist · 6th April 2005, 08:30 PM

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

lumanauw · 7th April 2005, 02:54 AM

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?

Nelson Pass · 7th April 2005, 06:38 PM

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.

Nelson Pass · 7th April 2005, 06:40 PM

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.

Netlist · 7th April 2005, 08:33 PM

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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6th April 2005, 12:36 PM	#2
lumanauw diyAudio Moderator Emeritus Join Date: Oct 2002 Location: Bandung	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?

6th April 2005, 08:04 PM	#3
Nelson Pass The one and only Join Date: Mar 2001	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.

6th April 2005, 08:07 PM	#4
Netlist diyAudio Moderator Join Date: Jan 2003	Interesting, but why not use a simple zener? /Hugo

6th April 2005, 08:22 PM	#5
Nelson Pass The one and only Join Date: Mar 2001	Just to be bad and confuse everybody.

6th April 2005, 08:30 PM	#6
Netlist diyAudio Moderator Join Date: Jan 2003	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

7th April 2005, 06:40 PM	#9
Nelson Pass The one and only Join Date: Mar 2001	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.

7th April 2005, 08:33 PM	#10
Netlist diyAudio Moderator Join Date: Jan 2003	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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