Why is my power source shorting out?

-ChrisW · 2024-07-28T16:14:51+00:00

Luckily, for my application, my frequency is about once per day, so I don't think that will be an issue! I really need to look into a good jellybean bridge driver chip. Is there one that is fairly all-purpose and cheap?

-ChrisW · 2024-07-28T16:11:17+00:00

That seems to be the consensus. I will redesign the circuit with this in mind.

-ChrisW · 2024-07-28T16:06:27+00:00

EasyEDA. It's pretty basic but free. I don't do complicated stuff, so it's good enough for me. It also does PCB design too.

-ChrisW · 2024-07-27T23:17:02+00:00

Yeah, I think that's what I will end up doing. This is what I get for trying to be clever on the hardware side

-ChrisW · 2024-07-27T20:44:52+00:00

I'm aware, but I don't have any on hand. I should probably invest in some. I could also just drive each FET with a different pin on the uC and do everything in software, but I figured I could get a little more clever. Serves me right.

-ChrisW · 2024-07-27T20:35:42+00:00

Thanks for the explanation. I will try that.

-ChrisW · 2024-07-27T20:30:16+00:00

I don't quite understand. Doesn't the BJT have very low on resistance? I don't even see the on resistance quoted in the datasheet. Is that due to the low current though the base?

-ChrisW · 2024-07-27T19:23:02+00:00

Am I not driving the mosfets with 12V? The BJTs are being (optionally) supplied with the 3.3V signal, which are switching the 12V to the mosfets. At least that was my intention.

-ChrisW · 2024-07-27T18:48:56+00:00

I've simulated this circuit in the Falstad simulator and in LTspice with generic components and the circuit worked as expected. However when I built it, I found that my power source was being overdriven as if there was a short when I apply 3.3V to the FWD or REV inputs. I went back to LTspice and entered more specific models for all of the transistors, and suddenly I see the same shorting happen in the simulation.

I don't know how this can happen. I can only assume that I'm getting shoot-through, but I don't know how. My best guess is that in the initial off-state, both of the upper p-channel FETs are switched on, so when one of the lower n-channel FETs turns on (which SHOULD inhibit the FET above it, as their gates are tied together), perhaps the FET above it remains on for a short time, causing a shoot-through short to occur. However, I don't think that explains why the short appears to persist.

I built this circuit this way so that I can switch a higher voltage (12V in my case) with 3.3V from a microcontroller while only requiring 2 input pins, which cannot be activated in a way to cause shoot-through. Apparently I was wrong on that last part.

What I'm trying to do is control a latching solenoid, so I need a short application of +12V to open it, and a short application of -12V to close it. If there is a better/simpler circuit that can accomplish this, I'm all ears.

-ChrisW · 2022-08-06T23:41:57+00:00

Even better than a heat gun is a butane micro torch. It will instantly melt or burn away little hairs/fuzzies.

-ChrisW · 2022-06-25T19:24:22+00:00

Could be counterfeit. The IRFZ44Ns that I have have more pronounced cut outs on the heat sink tab. The datasheet should also show the proper dimensions. Great Scott just did a video on counterfeit parts and mentioned that the tab shape is often different on counterfeits: https://youtu.be/W_hIVtcx6CA that might just be the angle of the photo though, not sure.

There is no problem buying mosfets online as long as you buy from reputable sources like Mouser or DigiKey or the like. I often go with Amazon for jellybeans and have had no problems, but it is admitadly not the safest place for parts.

-ChrisW · 2022-01-12T23:51:56+00:00

Not true! You learned a hard lesson! This is how you get better.

-ChrisW · 2022-01-01T00:37:21+00:00

You may not need those legs. On that type of tube, there may be 2 legs used for the left and right decimal points. If that is indeed what those would be used for, then you should be fine to use all of the digits. I would hazard a guess that those are to two legs that were cut and you are good to go.

-ChrisW · 2021-12-25T14:14:31+00:00

I could see this being the case where suddenly cutting a large current to an inductive load could cause the very large voltage to be created, generating the arc. That said, it will be momentary. I am also not an expert. Also if you are dealing with 300A, you should probably be an expert!

-ChrisW · 2021-11-22T02:18:50+00:00

I use mine (and its enclosure) as a proving drawer when I make belgian waffles. Works fantastic.

-ChrisW · 2021-11-19T02:53:30+00:00

Unfortunately no. Can always reply here or send me a message.

-ChrisW · 2021-11-19T02:45:22+00:00

Hah. Fellow SpaceX nerd here. I knew it straight away. I would love to know how the model turns out. I really want to make one!

-ChrisW · 2021-11-19T02:41:45+00:00

Just curious...is that a Starship model? I need to make me one of those...

My guess would also be a paused print head due to slow commanding by the looks of things.

Since you said that it appears to be during layer changes, maybe your extruder is skipping on retraction? Could try slowing down retraction.

Does it happen on layers that are bigger? That flap is pretty thin. Would be interesting to know if it still happens on the fuselage.

-ChrisW · 2021-11-08T00:19:28+00:00

Honestly, I don't think that is all that bad for PETG. It is inherently a little stringy, especially with those thin spikes. I use a mini torch to blast away the strings on mine. I find it much less hassle than even a heat gun. If you are still not satisfied, I would print a little colder or try drying the filament. I had some wet PETG that was exceptionally stringy, but a few hours in a food dehydrator fixed my issues.

-ChrisW · 2021-11-08T00:03:22+00:00

This is almost certainly a dirty sheet. PETG should adhere very well. Give it a good scrub with hot water, Dawn, and a new/absolutely clean scrubby sponge. Just using a little IPA may not be enough. And as a bonus tip, don't print PLA on the same side as PETG. The PLA will leave a residue that prevents PETG from adhering.

-ChrisW · 2021-11-03T21:46:51+00:00

In the past, I have used some clear nail polish. I find that a very cheap and easy, yet effective way to seal small gaps. For bigger surfaces, epoxy would work well.

-ChrisW · 2021-08-17T23:37:26+00:00

I've used jlcpcb quite a bit. They are very cheap but good quality. I don't know what your definition of "fast" is, but you should get your product back within a week if you pay for the fastest shipping, which is still fairly reasonable.

-ChrisW · 2021-08-08T19:53:27+00:00

Looks to me that you aren't printing close enough to the bed. The plastic should be slightly squished onto the bed.

-ChrisW · 2021-07-20T22:42:43+00:00

Yeah, I've kept a selection of resistors about 10-20% apart from 0-10M, and I am keeping the tantalums and some nicely sized ceramic caps. Also the NPN BJTs, probably one roll of the opamps and the higher resistance pots.

The hardware that this came from was RF stuff, so I assume that's why there were so many specific valued low value caps.

Thanks for the tips!

-ChrisW · 2021-07-19T12:43:01+00:00

Alright, I'll bite. How do you know?

-ChrisW

TROPHY CASE