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Fool'n around with DSO & AWG
MikeP:
For the purity of the experiment, current feedback should be eliminated. I'm talking about the emitter resistor. The entire test setup must be grounded at the emitter. Accordingly, the current signal from the resistor will appear in an inverted form.
HighVoltage:
--- Quote from: mawyatt on September 17, 2022, 07:12:25 pm ---
#90 was using a custom HV amplifier (we developed awhile back to augment the AWG, details somewhere here on EEVblog) connected to AWG to sweep the voltage higher to show beginning 2N3904 collector breakdown, note horizontal (DSO Ch1) scale factor.
--- End quote ---
Interesting setup, thanks for sharing!
Can you point to the HV amplifier thread, somehow I can not find it.
mawyatt:
--- Quote from: MikeP on September 18, 2022, 07:08:55 am --- For the purity of the experiment, current feedback should be eliminated. I'm talking about the emitter resistor. The entire test setup must be grounded at the emitter. Accordingly, the current signal from the resistor will appear in an inverted form.
--- End quote ---
Yes this would be the proper method, and why it's mentioned in the above (#8) if we were going to design and build a proper Curve Tracing Fixture using a Transimpedance amp which moves the current sense resistor into the feedback loop and forces the emitter node to virtual ground. Of course one also could move the current sense resistor above the collector and use a differential voltage probe across said resistor.
Anyway, the kludge setup shown here was just for some fun playing around :)
Best,
mawyatt:
--- Quote from: HighVoltage on September 18, 2022, 10:53:00 am ---
--- Quote from: mawyatt on September 17, 2022, 07:12:25 pm ---
#90 was using a custom HV amplifier (we developed awhile back to augment the AWG, details somewhere here on EEVblog) connected to AWG to sweep the voltage higher to show beginning 2N3904 collector breakdown, note horizontal (DSO Ch1) scale factor.
--- End quote ---
Interesting setup, thanks for sharing!
Can you point to the HV amplifier thread, somehow I can not find it.
--- End quote ---
Sure, here's a couple that you might find interesting. The one we used is based upon the OPA462 HV Op-Amp.
https://www.eevblog.com/forum/testgear/hv-buffer-amp-for-awg/msg3623953/#msg3623953
https://www.eevblog.com/forum/testgear/cheap-diy-high-powervoltage-awg-buffer-amp/msg3449784/#msg3449784
https://www.eevblog.com/forum/testgear/awg-buffer-amp/msg3368650/#msg3368650
Best,
mawyatt:
Here's a few more interesting plots using this setup with just voltage sweeping the device.
#99 is a 6.2V Zener at 1ma/div with 100 ohm sense R
#100 is a 1N4733 Zener (5.1V)
#101 is a 1N4799 Zener (24V)
#102 is a 1N5817 SBD, note the low froward conduction voltage SBD are noted for
#103 is a very interesting plot, note the zero axises are moved to the lower left corner for a better display. This is a reversed (exchanged collector and emitter) 2N3904 with base connected to ground thur a 100K. A 1K is used from the collector to ground for current sensing (500mv/1K or 500ua per div) for CH2 and 10K is to the emitter from the + sweeping voltage with the AWG feeding the mentioned HV amplifier. Scope CH1 is across the emitter to ground to show the DUT voltage.
Note the negative incremental resistance (dV/dI) exhibited by the voltage across the reversed 2N3904 folding back occurring ~11V while the current is increasing, thus dV/dI is negative!! As the current continues to increase the negative resistance subsides and goes thru zero ~700ua and then become positive.
Just to proof to ourselves we were actually "seeing" a negative resistance, we attached a 1uF Mylar capacitor from the emitter to ground and set the AWG sweep to produce ~13.3VDC across the DUT, which produces about 250ua current, right in the middle of the negative resistance range as shown in plot #103.
#104 shows the classic relaxation oscillations created by the negative resistance reversed 2N3904.
Anyway, hope some folks find this stuff interesting!!
Best,
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