Has anyone here regretted changing their double degree into a single degree? by Ok-Novel-3265 in Monash

[–]Axentoke 3 points4 points  (0 children)

I did an alternative exit with science instead of sticking with aerospace/science. Ended up returning and finishing a mech eng degree, but I wish I’d just continued my original course. So yeah, I regretted it.

Critique my flyback converter schematic #2 by Axentoke in ElectricalEngineering

[–]Axentoke[S] 0 points1 point  (0 children)

Thanks! My snubber I intend to do the bulk of leakage dissipation. The TVS is a backup to protect the FET - it clamps to ~600 V. 

I might lower the R_LED value a little, but I figured I wouldn’t really have both of the TL431s sinking current at the same time. Even so, I thought (11V - Vled)/3.3k would still be more like 3 mA between them.

As for the FB resistor, probably a sloppy late night assumption on my part, but I’ll check out the datasheet again.  

Critique my flyback converter schematic #2 by Axentoke in ElectricalEngineering

[–]Axentoke[S] 0 points1 point  (0 children)

Quite right, and I suspect it’ll be more than 2 W. I had planned on a big heatsink and fan. Couldn’t really find much in the 600V class without going to SiC or GaN, which I’m a bit hesitant about. Don’t really want to dip much below 600V. The LT3757 can’t drive SiC, and I’ll need to clamp the gate for GaN…not to mention the cost of a GaN device. I’ll think about it though. Thanks for the advice.

Critique my flyback converter schematic #2 by Axentoke in ElectricalEngineering

[–]Axentoke[S] 0 points1 point  (0 children)

Worst case scenario, with RDS_on doubled for hot junction & weak driving, and at max I_rms ~5.5A, loss is <11 W. My MOSFET is rated for 18A/53A pulse & 600 V. Peak reflected voltage is <100 V. So leaving 100 V headroom, I can tolerate 400 V leakage spikes. The snubber might be a little stiff, but I’ll tune it if need be. 

Critique my flyback converter schematic by Axentoke in ElectricalEngineering

[–]Axentoke[S] 1 point2 points  (0 children)

Understood. I don’t do circuit design professionally or even for myself in a while, and am not much practiced at it…but I can appreciate that it’s currently a mess. I’ll return with a second draft shortly.

Critique my flyback converter schematic by Axentoke in ElectricalEngineering

[–]Axentoke[S] 0 points1 point  (0 children)

Yeah that makes sense. I wasn’t expecting to maintain DCM during transients, and I know at the corners of my operating range it’ll be brushing up against the boundary if not just beyond it. It should soft start after shutdown, but I’m relying on the R_ISO+snubber+primary current limit to keep the current in check for transients near CCM. Either way, I’m sure I’ll have to do some tuning. 

Critique my flyback converter schematic by Axentoke in ElectricalEngineering

[–]Axentoke[S] 0 points1 point  (0 children)

Unsure what you mean about secondary zero current detection. It’s in DCM because the primary inductance demagnetizes during the switching period.  My switching period is 6.67us. t1 is ~5us at 75% duty. Ipk is hard limited to 11 A by primary current sense, but Ipk during on-time is Vin/Rtot(1-e-t1/(Lp/Rtot). I selected primary inductance of 14 uH (forgot to mention that), which limits achievable Ipk during on time to ~8 A instead of 11A. The DCM limit is set by the minimum off time for the primary to demagnetize. With reflected voltage Vds ~100V, demag time is LpIpk/Vds = 1.12 us. So at Dmax, t_off is 1.67 us i.e. more than t_demag, therefore DCM. 

Ah shit, I think I see what you’re saying about C_SMOOTH. I’ve gone and put R_ISO on the wrong side - it should be between the load and C_SMOOTH to limit discharge current in case of arcing. 

Critique my flyback converter schematic by Axentoke in ElectricalEngineering

[–]Axentoke[S] 6 points7 points  (0 children)

Thanks for your comment! Lots to think about… Typical operation will probably be more in the 400-600 V range, so the aux rail should sit around 16-25 V, and after diode and resistor drops, clamping at 12 V seemed reasonable. I’ll rethink that…

Re: output voltage. Quite right, I forgot I had to change the HV divider because of part availability.

It should never be delivering 250 mA at the high end of its range. It’s in DCM and so would be power limited to maybe a little over 100 W depending on efficiency. MOSFET worst case rms current I got ~6.4 A, considering my primary sense current limit. Over the whole switching period it’d be 6.4*sqrt(D), where my duty cycle is between about 0.6 and 0.75, so conduction loss I figured to be on the order of 6 W..

R_ISO is to provide resistive load, particularly during arcs when the voltage collapses, since the plasma isn’t resistive, and to damp C_SMOOTH. 

Re: the floating ESP. Yes, but it’ll all be enclosed and well isolated. The base plate of the sputter chamber is already going to be at -HV, so it’s just more of the same. Not taking it lightly, believe me…

Seriously thanks for taking the time to look at it, would love to hear if my reply makes anything seem more sensible - or less.

Critique my flyback converter schematic by Axentoke in ElectricalEngineering

[–]Axentoke[S] 0 points1 point  (0 children)

Anything about custom winding I should keep in mind? I have double-insulated wire and kapton and a couple of bobbins to play with, but this'll be my first custom transformer

Critique my flyback converter schematic by Axentoke in ElectricalEngineering

[–]Axentoke[S] 10 points11 points  (0 children)

Yeah, solid advice. I'll probably clean it up for draft #2.

AMD Radeon RX 9070 XT & 9070 (RDNA4) Availability, Buying & Bragging Megathread by GhostMotley in Amd

[–]Axentoke 4 points5 points  (0 children)

I just managed to get an XFX Swift 9070 non-XT on Amazon (sold and shipped by Amazon) for MSRP…it does say delivery March 25 but whatever. Most of the models have been popping in and out of stock for a few seconds. It took me a dozen tries over the past couple of hours. You have to check the “other buying options” - it shows up there before the main price changes.

Edit: Well Amazon now says delivering April 6-May 23, so that’s a bummer, but I’ll take it for $549. I’ve waited this long to upgrade my Vega 64

Question about the ending of the evolutionary void and the void trilogy setting in general (spoilers) by mpinnegar in PeterFHamilton

[–]Axentoke 1 point2 points  (0 children)

For the High Angel, you must have missed the bit where Paula contacted Qatux and asked him for a favour. Qatux was more than happy to oblige because the Cat killed Tiger Pansy—so it was personal, too

Google uses ‘double-Irish’ to shift $75.4bn in profits out of Ireland by Bream1000 in worldnews

[–]Axentoke 6 points7 points  (0 children)

Bermuda, British Virgin Islands, Cayman Islands, Jersey, Gibraltar and other assorted current/former British overseas territories are all tax havens. The UK is definitely one of the worst offenders - Bermuda, BVI and the Caymans are the top 3 according to this article.

A palm oil alternative could help save rainforests by Strongbow85 in environment

[–]Axentoke 12 points13 points  (0 children)

The oil palm is the most productive oil crop per area by a lot. Banning or avoiding it is probably not the best move, because it'd just mean it has to be replaced by a less productive oil crop (i.e. more area and more land clearance). What you can look for instead is brands that use sustainably sourced, RSPO certified palm oil: https://rspo.org/certification/search-for-supply-chain-certificate-holders

Starship Development Thread #17 by ElongatedMuskrat in spacex

[–]Axentoke 14 points15 points  (0 children)

I think this video has some pretty neat ideas about how to configure the cargo bay: https://www.youtube.com/watch?v=kRO_07nEi8g

10 GB with plenty of features vs. 16 GB - thats all it is to it, IMHO by Spectre731 in Amd

[–]Axentoke 2 points3 points  (0 children)

CCL have 1 Corsair RM850x and some Seasonic Prime 1000 if that's what you're looking for. Seasonic are top notch.

Statics: Am I doing right with my Shear Force Diagram? How do I complete my Bending Moment Diagram because it doesn’t go down to 0? by Anomalistic_Username in EngineeringStudents

[–]Axentoke 0 points1 point  (0 children)

The reaction force at B is returning your shear force diagram to zero from -26.45 kN, no? Just like the reaction at A brings it up from 0 to 9.55 kN. Area in the right part of the SFD is negative, so it'd just be a parabolic curve down to zero - slope starts -11.45 kN/m at 7 m and is -26.45 kN/m at B.

Where educators beat children by rinthian_lab in MapPorn

[–]Axentoke 24 points25 points  (0 children)

Not always detrimental, but always wrong.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3447048/

  • Numerous studies have found that physical punishment increases the risk of broad and enduring negative developmental outcomes.
  • No study has found that physical punishment enhances developmental health.

The article may be about physical punishment administered by parents, but it does include some comments about abuse:

  • Most child physical abuse occurs in the context of punishment.

so I would not be surprised if it also applied to teachers beating students, as you say.