Made a curve tracer finally but it’s exceeding the current limit of my power supply. I’m curious to know how much current other people’s builds draw.
My linear power supply uses the LT3097, a positive and negative <=15V linear regulator with current limiting set to ~45mA on each of the outputs. It works great. I can’t recall why I limited current to 45mA so now I wonder if that was a mistake.
My curve tracer uses CMOS TL072/TL074 purchased from Digikey. Due to space constraints, I had to do my own board layout using surface mount components but I’m confident it’s all correct. There are no shorts but I do measure ~225ohm between the + and – pads on my curve tracer board and by examining the schematic, I can see these tracks go only to the two opamp ICs. I can’t imagine that I destroyed an opamp during assembly but I suppose it’s possible.
I think Paul used jfet opamps in his design but I breadboarded the oscillator section and it worked great so I was confident to proceed with the build.
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So please, if some of you could measure the current draw of your curve tracer and share that with me, I sure would appreciate it.
Hi, it’s extremely easy to find out how much current your curve tracer takes by putting an ammeter in series with one rail and feed the project from a power source that doesn’t limit the current or is at least 150-200mA / rail. So once you found the maximum current that is consumed while testing something say a short circuit or something, then tune your diy PSU accordingly making sure you allow some 10-15 % current as spare on top. That’s it. Job done.
To fix
<a href=” removed link ” target=”_blank” rel=”noopener”>Schematic
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Others have used https://imgur.com/ to post photo their photos using the Direct Link.
Larry – N7LUF
Got it. I’ll share what I discovered so others may learn from my mistake.
Firstly, each op amp in a tl07x package exhibits a max quiescent current of ~1.1mA so we’re still looking at 6 opamps in the design or 6.6mA minimum current draw. Now, each opamp has it’s output limited to +-26mA in a short circuit situation for a theoretical max current draw on 156 + 6.6 = 162.6mA. Close enough.
So I thought I must have shorted at least two outputs and while verifying, I discovered a grave error made while printing the board layout: The pads were mirrored wrong.
@mikemike to be fair, I never measured the current draw since my power supply uses the LM317 and LM339 pair and can deliver up to 1 Amp and that is most likely 15 times over what is needed since my estimation is in the ballpark of 60-80mA or thereabout. But, as long as it works as it should and considering is using a little mains transformer I had no desire or need to measure it. But If I was using a battery based PSU then in that case I would have definitely measured the current consumption.
Now, my build is a complete redesign of the PCB because I used the SMD style components instead. So, a little different than the original design and way way smaller as well. 🙃
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