I was playing with the Tektronix 576 that I recently purchased, testing transistors and getting familiar with its use.
I used to check the hfe of transistors and do some basic hfe matching with one of those cheap M328 transistor/component testers that are so popular online, so I thought it would be good to do a comparison of the hfe on a series of transistors.
I measured a 2N304, a BC447, an S8550 and a BD139.
For the first 3, the hfe values from the transistor tester were pretty much spot on, for the BD139 it was higher by about 150.
I got another BD139, to repeat the same measurement, and again the cheap transistor tester was higher by about 180. The curve tracer gave me an hfe for the two BD139 of approximately 250, which matches the specs.
Has anyone else noticed this strange behaviour? It is quite strange that for some types of transistors the hfe values of the curve tracer are so off, whereas they can be pretty much spot on for others. 😕
I used to check the hfe of transistors and do some basic hfe matching with one of those cheap M328 transistor/component testers that are so popular online, so I thought it would be good to do a comparison of the hfe on a series of transistors.
I measured a 2N304, a BC447, an S8550 and a BD139.
For the first 3, the hfe values from the transistor tester were pretty much spot on, for the BD139 it was higher by about 150.
I got another BD139, to repeat the same measurement, and again the cheap transistor tester was higher by about 180. The curve tracer gave me an hfe for the two BD139 of approximately 250, which matches the specs.
Has anyone else noticed this strange behaviour? It is quite strange that for some types of transistors the hfe values of the curve tracer are so off, whereas they can be pretty much spot on for others. 😕
Are we considering the currents employed? Transistor gains are at currents. A curve tracer should present different currents to show you curves. A hand tester won't do that, it has one current.
Consider the common 1N4007 diode. The rating on the ON Semi data sheet is 1.1v forward. But that is at the rated 1A current. Just measuring with my hand meter, I usually see under half a volt. That is at very low current.
Consider the common 1N4007 diode. The rating on the ON Semi data sheet is 1.1v forward. But that is at the rated 1A current. Just measuring with my hand meter, I usually see under half a volt. That is at very low current.
The cheap curve tracer measures at a Ic of 6.2mA and a Vce that must be lower than 4V as that is the voltage of its fully charged battery. At those values (or around those), the hfe of the BD139 should be between 25 and 250, which is what I get from the Tek576 (I tested 3, all 3 gave me a 250 gain), whereas the cheap component tester gives me values from 380 to 430 depending on the which of the three I measured.
I have owned a TEK 576 with the high current module. But most of the time I want to just match transistors. The cheap-o transistor tester is fine for that - even if the Hfe value is not accurate.
Even something as simple as this is good for matching (compliments).
The TEK is best at measuring a host of parameters of a transistor not just Hfe.
If in doubt, I would trust the TEK.
-RNM
Even something as simple as this is good for matching (compliments).
The TEK is best at measuring a host of parameters of a transistor not just Hfe.
If in doubt, I would trust the TEK.
-RNM
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