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Electronics => Projects, Designs, and Technical Stuff => Topic started by: RonFred2 on May 01, 2021, 09:19:24 pm

Title: Transistor Curve Tracing Shows Weird Scope Display
Post by: RonFred2 on May 01, 2021, 09:19:24 pm

I recently crafted a transistor curve tracer with my Oscilloscope and Arbitrary Waveform Generator. Most BJT Si transistors show typical/normal traces but one device undertest produces abnormal trace when collector-emitter voltage (Vce) goes higher than about 6 Volts.

Does anyone know what is the cause of this abnormal trace?

I present a few images below showing my test setup, a good trace, and the weird trace.

http://www.biophysicslab.com/2021/04/27/testing_transistor_hfe/#measure-hfe-using-an-oscilloscope-and-arbitrary-waveform-generator-awg (http://www.biophysicslab.com/2021/04/27/testing_transistor_hfe/#measure-hfe-using-an-oscilloscope-and-arbitrary-waveform-generator-awg)

Title: Re: Transistor Curve Tracing Shows Weird Scope Display
Post by: T3sl4co1l on May 01, 2021, 11:15:21 pm

I suppose it's not inverted as hFE looks reasonable.  Just defective then?

Negative resistance is normal avalanche operation -- but this normally occurs between Vceo and Vcbo, over 60V for 2N3906.

Tim

Title: Re: Transistor Curve Tracing Shows Weird Scope Display
Post by: RonFred2 on May 05, 2021, 01:30:08 am

Someone on another forum had this to say about this circuit and transistor behavior, with one other person agreeing...

Quote

Looks like the CE junction got zapped and acts as a SCR with a negative incremental resistance . Might be good for a tunnel diode oscillator at RF if biased at -7V.;)This is a breakdown arc failure with say 40K/mm might be 40V/um so 7V is about a 175 nm gap that the E-Field bridged This PNP should be good to -40V and act like a Zener near -50V.

I thought this contribution may help others who look at this issue as well.

Thank you all for looking at my forum post here.