Electronics > Projects, Designs, and Technical Stuff
Curve tracer designs?
Wolfgang:
Love it. POOGE at its best ! :)
rhb:
I wanted to build one of these many years ago, but never got around to it.
In 2018 I have to ask a simple question.
Why would you not use a fast ARM MCU with stereo ADC/DAC feeding suitable op amps? One channel for the base drive and one for the collector with the ADC taking readings.
I have a Peak Technologies DCA75 which does a decent job, but it only reports Vbe_sat and Vce_sat. It will do curve tracing with the PC software. My BSIDE ESR02 Pro reports Vbe_turn_on, but not Vbe_sat, etc.
I've not done any in depth analysis of what a good transistor tester should do, but it seems to me that there is room for considerable improvement at low cost.
0culus:
--- Quote from: johnwa on November 21, 2018, 10:23:32 am ---Hi,
Here is an overview of a curve tracer I built recently, don't know if this is of any help:
It all started when I was wondering what to do with this old oscilloscope that a friend gave me some years ago. I already had an analogue scope, and I was thinking of giving this one away to some deserving newbie, but it was in pretty poor shape: noisy switches, timebase not working, and I had already needed to make a repair to the EHT supply using the tripler out of an old TV set. So I decided, rather than burden someone else with it, I would convert it into a dedicated curve tracer.
To provide the drive signal, I used an amplifier out of some old PA equipment. This circuit used a couple of quasi-complementary 2N3055s, and was good for about 40W into 8 ohms. Conveniently, I managed to find some suitable +/- 35V supply rails inside the scope to power it. Maximum output swing is about +/-33V.
For the oscillator, I got lazy, and ordered a sine/square/triangle signal generator module from ebay, for the grand sum of $3.50. This feeds a front panel attenuator (I repurposed some of the controls in the timebase module), and some switchable level shifting to provide positive, negative, or AC output. I also added an adjustable current limiting circuit to the amplifier. (Let me know if you would like details).
The output of the amplifier is connected to the CH1/X input, which then becomes the drive output. The CH2 input has a 1 ohm resistor connected across it, to act as a current shunt. The input attenuators work as normal, with the CH2 one being recalibrated in amps instead of volts.
I also added a base drive staircase generator, based on the Elektor December 1989 circuit. (I think someone may have posted this on the forum somewhere - search around)
In the picture, the original X deflection board is at the back, then comes the amplifier module. The function generator is at the top, with the staircase generator below it. The current limiter is partially hidden behind the heatsink.
Edit 21/11/2018: spelling
--- End quote ---
Oh that's really neat! Thanks for sharing. That would be a totally awesome use for an old scope in the future.
--- Quote from: rhb on November 23, 2018, 03:27:13 pm ---I wanted to build one of these many years ago, but never got around to it.
In 2018 I have to ask a simple question.
Why would you not use a fast ARM MCU with stereo ADC/DAC feeding suitable op amps? One channel for the base drive and one for the collector with the ADC taking readings.
I have a Peak Technologies DCA75 which does a decent job, but it only reports Vbe_sat and Vce_sat. It will do curve tracing with the PC software. My BSIDE ESR02 Pro reports Vbe_turn_on, but not Vbe_sat, etc.
I've not done any in depth analysis of what a good transistor tester should do, but it seems to me that there is room for considerable improvement at low cost.
--- End quote ---
While that would likely work, I personally prefer analog test equipment. :) My main scope is a Tek 2465B.
rhb:
Certainly a valid reason. I bought a refurbished Tek 485 from Reed Dickinson via eBay precisely to have an analog scope to double check strange stuff from DSOs.
0culus:
I will probably try to get a decent digital scope at some point to have access to the nice features they have, but I certainly wouldn't want it to be my only scope!
On another note, I tried building another prototype of this circuit with some better caps and I am pretty sure the design originally mentioned in the OP doesn't work.
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