Electronics > Projects, Designs, and Technical Stuff
Curve tracer designs?
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0culus:
So I've been thinking that it would be handy to have a curve tracer in my lab, but even more, it would be fun to make it myself. I've looked at a variety of designs, some requiring mains voltage, some not. I tried soldering this one up on a protoboard today because I have all the parts on hand and no transformer required (except I omitted the switch for a prototype): http://www.electronics-lab.com/diy-generic-curve-tracer/

But, it seems to not be working at all, mainly the 3904 never starts oscillating so there's no signal being put through the DUT.

Are there better designs for a curve tracer that are similarly parts-efficient? Thanks!
JoeO:
The schematic shows a 3M resistor while the parts list calls out a 2M resistor.

Have you tried them both?
0culus:

--- Quote from: JoeO on November 18, 2018, 03:00:56 am ---The schematic shows a 3M resistor while the parts list calls out a 2M resistor.

Have you tried them both?

--- End quote ---

Yeah, I tried 3Mohm too and it still doesn't work. There's 0.584 V on the base of the transistor and 6.160 V on the collector in that arrangement, and there is nothing at the emitter. Fairly sure the transistor isn't backwards.
SeanB:
Try another 2N3904, and what capacitor are you using for C1, C2 and C3, they need to be 63V or higher mylar foil types, as ceramic or electrolytic capacitors leak way too much. Bias is turning the transistor on, but either there is leakage or a bad connection.
0culus:

--- Quote from: SeanB on November 18, 2018, 09:24:20 am ---Try another 2N3904, and what capacitor are you using for C1, C2 and C3, they need to be 63V or higher mylar foil types, as ceramic or electrolytic capacitors leak way too much. Bias is turning the transistor on, but either there is leakage or a bad connection.

--- End quote ---

OK. I only have a few of those kind of caps unfortunately, and not in the right spec. Guess it's time to order some. The 4.7nF ceramics I have don't seem to be leaking DC, but the 1uF electrolytic I used is definitely leaking.
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