killed BJT

zilog · 27th May 2008, 09:54 PM

I have wired a NPN BJT in the manner shown in this schematic

with the result that it is internally open.. I need to sometimes have the emitter a few volts higher than the base, do I need a diode in series with the emitter, or have I experienced something weird?

Juergen Knoop · 27th May 2008, 10:34 PM

a diode would help, otherwise you would have to limit the breakdown current to a few mA.
I don't know what is considered a safe current.
regards

ilimzn · 27th May 2008, 10:36 PM

Base-emitter reverse break down voltage is on the order of 8V, which means you ran an 8V zener from a 15V source with no current limit - in other words, you killed it.
If you need the B-E junction reverse biassed, you will need some form of protection, either a series diode or a parallel diode, depending on the particular case.

zilog · 27th May 2008, 10:53 PM

Thanks,

I had completely overlooked that parameter.

Mooly · 28th May 2008, 07:28 AM

Hi,
Running as shown in post 1 (current limited) will generate a lot of "white noise" across the junction. This was the classic white noise generator 30 years or so ago.
Regards Karl

27th May 2008, 09:54 PM	#1
zilog diyAudio Member Join Date: Oct 2005	killed BJT I have wired a NPN BJT in the manner shown in this schematic with the result that it is internally open.. I need to sometimes have the emitter a few volts higher than the base, do I need a diode in series with the emitter, or have I experienced something weird?

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27th May 2008, 10:34 PM	#2
Juergen Knoop diyAudio Member Join Date: Jan 2007 Blog Entries: 3	a diode would help, otherwise you would have to limit the breakdown current to a few mA. I don't know what is considered a safe current. regards

27th May 2008, 10:36 PM	#3
ilimzn diyAudio Member Join Date: Feb 2005 Location: Zagreb	Base-emitter reverse break down voltage is on the order of 8V, which means you ran an 8V zener from a 15V source with no current limit - in other words, you killed it. If you need the B-E junction reverse biassed, you will need some form of protection, either a series diode or a parallel diode, depending on the particular case.

27th May 2008, 10:53 PM	#4
zilog diyAudio Member Join Date: Oct 2005	Thanks, I had completely overlooked that parameter.

28th May 2008, 07:28 AM	#5
Mooly diyAudio Member Join Date: Sep 2007	Hi, Running as shown in post 1 (current limited) will generate a lot of "white noise" across the junction. This was the classic white noise generator 30 years or so ago. Regards Karl

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