Hello, I'm very much a beginner with electronics and I just got an oscilloscope so I have a few (probably quite dumb) questions...
I've built a 12vdc to 200vdc boost circuit designed for driving nixie tubes using this diagram
.
I built it on perfboard using this layout
.
Now when I probe the output of it under load I get this:
Which is mostly what I would expect except for those short >10v spikes every time at the start of a boost cycle. And I've measured if before with no load attached and the spikes could reach 30v.
Then I measured the timing pin on the mc34063 chip and at first it looked like it was at 12v and I was like wtf is going on but zooming in further reveals a normal looking clock line but with short spikes similiar to those on the output:
.
1st question: What is causing the spikes, are they real? Or is the scope just picking up interference from the switching and I can safely ignore the spikes and maybe set a BW limit to not see them?
Or are the spikes caused by my crappy perf board layout or something like that?
2nd question: When I was playing around with the scopes coupling modes, there were one or two instances where I switched to AC coupling but the signal looked like it was still stuck in the DC mode. Switching around the modes and selecting AC again fixed it, but I'm wondering if its a sign I'm doing something terribly wrong or is it a bug with the scope?
3rd question... after doing the measurements and playing around I got kind of paranoid about the safety of probing this circuit with the scope. I've previously watched Dave's video on "How to not blow up your oscilloscope" and it left me with the idea that its generally safe to probe around if your D.U.T is connected to the wall with an adapter that does not use an earth pin. And to power the 200v booster I used a random $2 230vac to 12v DC power brick from ebay (uses only 2 prongs to connect to wall, no earth pin) But then I thought that I read somewhere that the mains earth is just connected to neutral (or that it can be). So out of curiosity I tested the resistance between the 12V dc output terminals and the mains earth and I got readings of about 1M ohms... I also tested with a DMM how much current can flow from the power bricks DC output to mains earth and I got like 4milliamps... when I tested voltage it spiked to a few volts on first contact but then went down to few millivolts.
So the "non earthed" power bricks DC output is somehow connected to mains earth? So... is it safe to to probe around devices powered by this and connecting the scope probes earth clip to anywhere? even though it looks like some current could flow and there might be a voltage difference?
Last question: on the scope near the BNC inputs it says "Max 400v pk". I know there are many threads about ppl asking about the max voltage input to scopes and I've read them but its still not 100% clear to me with using 10X probes.
I've seen people say that the 10X probe will just divide the voltage seen by the scope by 10, so in my case by that logic I should theoretically be able to probe a 4000v (4kv) signal with a 10X probe? Is this correct? I know the normal probes are only rated to like 300v on 10X modes, but I'm talking theoretically, if the probe could handle it.
I've also seen some people saying that you should never probe a voltage higher than the max voltage of the scope, even with a 10X probe, because the "AC coupling capacitor will charge to the original voltage" and blow up your scope regardless of the 10X probe. Or at least something along those lines. So what is the correct answer?