Measuring base spreading resistance - Page 4

Mark Johnson · 7th April 2018, 12:58 PM

It costs less than GBP 1,00 to purchase one. Now you can measure Vcesat at a variety of currents and a variety of temperatures.

jackinnj · 02:37 PM

Quote:

Originally Posted by Mark Johnson

It costs less than GBP 1,00 to purchase one. Now you can measure Vcesat at a variety of currents and a variety of temperatures.

Set the Vertical knob of your Tektronix 576 to "StepGen", the Horizontal knob to Collector and the Terminal Selector to "Emitter Grounded" and the vertical axis will display Ib, the horizontal axis Vce

(Unfortunately, the 576 doesn't give logarithmic results!)

jackinnj · 7th April 2018, 06:53 PM

Quote:

Originally Posted by Maxwell3

This is cool, thanks for doing all the look-up!

Can you use the Excel option to label each point with the transistor number?
It would be good to understand what is the difference between transistors that have vce(sat) near 0.01V and very low noise vs. the ones that have vcesat of 0.005V but more noise.

I labeled the datapoints in Photoshop.

Anyone, feel free to provide better Vce(sat) numbers.

Maxwell3 · 8th April 2018, 02:35 AM

Thanks! I looked at more specific examples. For example 2sd2653 and 2sb1690 clearly have Vce(sat) of less than 10 mV, while 2sc3601 and 2sc3955 have Vce(sat) of about 0.1V. Yet the noise of the first pair is a factor of 2 higher than the noise of the second pair. So, while low Vce(sat) seems to contribute to giving a low-noise transistor, its not the only necessary ingredient.

Perhaps someone can stare at the examples of these datasheets and identify another reason why some transistors might be better than others.

I am going to get some PBSS4021nz transistors, which have Vce(sat) of less than 1 mV, the lowest I could find, and try to measure their noise. I haven't done such measurements before, so it may take me some time to setup the amplifier circuit. If anyone already has a setup to measure the noise, feel free to beat me to it.

jackinnj · 8th April 2018, 11:23 AM

Quote:

Originally Posted by Maxwell3

... less than 1 mV, the lowest I could find, and try to measure their noise. I haven't done such measurements before, so it may take me some time to setup the amplifier circuit. If anyone already has a setup to measure the noise, feel free to beat me to it.

You just went "down the Rabbit hole, Alice".

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7th April 2018, 12:58 PM	#31
Mark Johnson diyAudio Member Join Date: May 2011 Location: Silicon Valley	It costs less than GBP 1,00 to purchase one. Now you can measure Vcesat at a variety of currents and a variety of temperatures.

8th April 2018, 02:35 AM	#34
Maxwell3 diyAudio Member Join Date: Apr 2018	Thanks! I looked at more specific examples. For example 2sd2653 and 2sb1690 clearly have Vce(sat) of less than 10 mV, while 2sc3601 and 2sc3955 have Vce(sat) of about 0.1V. Yet the noise of the first pair is a factor of 2 higher than the noise of the second pair. So, while low Vce(sat) seems to contribute to giving a low-noise transistor, its not the only necessary ingredient. Perhaps someone can stare at the examples of these datasheets and identify another reason why some transistors might be better than others. I am going to get some PBSS4021nz transistors, which have Vce(sat) of less than 1 mV, the lowest I could find, and try to measure their noise. I haven't done such measurements before, so it may take me some time to setup the amplifier circuit. If anyone already has a setup to measure the noise, feel free to beat me to it.