[HN Gopher] The magic of DC-DC voltage conversion (2023)
___________________________________________________________________
The magic of DC-DC voltage conversion (2023)
Author : _Microft
Score : 350 points
Date : 2024-09-11 03:53 UTC (19 hours ago)
(HTM) web link (lcamtuf.substack.com)
(TXT) w3m dump (lcamtuf.substack.com)
| crote wrote:
| > Between the resulting thermal management issues and reduced
| battery life, linear regulation is seldom worth the pain.
|
| I'd argue the exact opposite. The article is targeting
| "enthusiasts", and a _very_ large portion of enthusiast projects
| are going to be powered by a 5V USB charger and consume in the
| order of a few 100mA of power.
|
| LDOs are dirt cheap, widely available, have pretty decent output
| characteristics, and incredibly easy to use. If you have
| basically unlimited 5V and want 100mA of 3.3V, why _not_ use one?
|
| On the other hand, buck converters require you to actually do
| some actual engineering. You can't just haphazardly throw in a
| single IC and expect it to work flawlessly on your first try. You
| either have to use an (expensive!) fully-integrated module, or do
| a decent bit of math and part sourcing yourself. Neither option
| is exactly attractive to a hobbyist building a fairly simple one-
| off PCB.
| quacksilver wrote:
| Linear regulation is also very good when you have situations
| where you want to avoid generating unwanted noise or stray RF.
|
| Cheap buck converters are very noisy and annoying if you are
| building an audio or radio related project, or have such things
| nearby.
| f1shy wrote:
| In my experience, not only noise in the RF sense, but also
| audible. I put together a little audio amplifier, and the
| sound of the DC/DC makes it unusable in quiet situations. The
| 12kHz (coming physically from the converter, amplifier off)
| really hurts the ears!
| arghwhat wrote:
| That's magnetostriction, components under switching load
| (caps, inductors) need to be secured in place with an
| appropriate glue/putty.
|
| Using a higher switching frequency can also help, plenty to
| choose from.
| schoen wrote:
| Can that also help with the emanations security issue
| where an adversary might be able to extract usable data
| from the audio produced by the electronic components?
| mschuster91 wrote:
| TEMPEST and other side-channel hardening is _hard_ to do
| if you lack access to anechoic /RF isolated chambers,
| sensitive scopes/microphones and knowledge.
| kragen wrote:
| yes, but the audio usually doesn't travel as far as the
| rf; you'd almost have to be in a situation where the
| adversary can't put equipment near you but has managed to
| subvert a microphone
| foldr wrote:
| The usable data would just be "DC-DC converter is
| on/off". In theory, if the converter uses a variable
| frequency or duty cycle, you might be able to extract
| some information about that too. But that's not very
| interesting.
| arghwhat wrote:
| A DC-DC converter always uses a variable duty cycle to
| maintain the target output voltage (or for CC, current).
| Without it, the voltage would vary wildly depending on
| load.
|
| For something like an audio amplifier, obtaining precise
| power supply load would in turn give you a curve over
| amplifier load, which effectively gives you the speaker
| amplitude. Input caps and filtering will likely remove
| the high frequency components entirely, but you might be
| able to construct at least part of the played waveform.
| foldr wrote:
| All good points. I would say that it's a fairly
| outlandish scenario where you are (i) close enough to the
| device to listen to the caps whining but (ii) can't
| measure actual voltages within the circuit (which could
| be a lot more informative) and (iii) can't just listen to
| the audio output of the device directly.
| arghwhat wrote:
| Acoustic noise is one thing, but it's not at all
| outlandish to be within range of the EMI emitted from the
| same power supply which tells the same tale. What _is_
| outlandish is thinking anyone bothers listening in. :)
| arghwhat wrote:
| The noise would correlate with load, but this is the
| _least_ of your worries.
|
| Unless you have a proper RF testing lab and skilled EMC
| engineers at your disposal, the only thing you can do is
| stuff everything into a properly designed faraday cage.
| jimmyswimmy wrote:
| The other answer about magnetostriction is technically
| correct (the best kind) but Misses the actual cause, which
| is subharmonic oscillation. This occurs when you have not
| stabilized your control loop properly and is often the
| result of inadequate phase margin. A simple fix may be to
| allow the control bandwidth by increasing capacitance at
| the work amplifier output. But this may also make the
| response too slow.
|
| For most people designing DCDC converters, this is the most
| difficult part to understand and correctly tune. If you get
| the parts selection right and carefully lay out the
| circuit, this is the one that they can't get right. It
| takes some understanding of control theory or careful
| testing and tweaking. And it's what drives a lot of folk to
| the expensive and relatively inflexible power modules.
| megous wrote:
| Noise can also come from pulse-skipping mode of
| regulation, if you draw too little power from the DC-DC
| converter, and can go away under higher load.
| Animats wrote:
| > Cheap buck converters are very noisy and annoying...
|
| Yes. This is why the good ones have more parts. It's a
| totally fixable problem, and the parts cost to fix it isn't
| high, but it takes extra engineering effort.
| shiroiushi wrote:
| All true, but for a hobbyist it probably isn't worth it if
| their goal is to just build some little audio project.
| atoav wrote:
| You are right. Yet, if you asked me how to get less noise
| on your audio circuit the LDO is the easier answer that
| will cost you less time to implement and likely give you
| the superior result.
|
| Especially for beginners without a ton of measuring
| equipment and experience having potentially bursty high
| frequency components in series can be an interesting way to
| not get the thing they were planning done, but instead have
| to deal with an entire new set of problems whose existence
| they didn't even know about.
|
| Technically you are correct, but "just slap a LDO on it" is
| probably the better advice.
| Animats wrote:
| Agreed. I had to learn a lot to build one. I had an
| application so unusual (driving antique teletype machines
| from a laptop) that I had to do a unique design. For most
| low-volume applications, it's not worth the trouble.
| roaringraster wrote:
| And 3.3/5 is approximately 66% efficiency, which isn't too
| horrible. So even if you get your buck converter working,
| getting those 95%+ efficiency numbers you see in datasheets out
| of the circuit is not trivial.
| _fizz_buzz_ wrote:
| If you have 5V and have to step down to 3.3V using an LDO is a
| very reasonable choice (at 100mA you have about 170mW losses).
| However if you have e.g. 24V and need to step down to 3.3V, an
| LDO can get annoyingly hot (at 100mA you now have over 2W
| losses). But I agree, this is really a "it depends" situation.
| michaelt wrote:
| _> On the other hand, buck converters require you to actually
| do some actual engineering. You can 't just haphazardly throw
| in a single IC and expect it to work flawlessly on your first
| try._
|
| It used to be a hassle a few years ago - but these days you can
| haphazardly throw in a R-78K3.3-0.5 - which has the pinout of a
| classic three-pin 3.3v linear regulator, but it's actually an
| 80% efficient DC-DC converter with 500mA output and an input
| range that goes up to 36v.
|
| That's enough current even if you've got something like an
| ESP32 that needs 250mA - and for any type of hobby project, the
| $2.40 is fine.
| progbits wrote:
| I can highly recommend the MIT 6.622 Power Electronics course
| recently released on OCW:
|
| https://youtube.com/playlist?list=PLUl4u3cNGP62UTc77mJoubhDE...
|
| https://ocw.mit.edu/courses/6-622-power-electronics-spring-2...
|
| Prof. David Perreault is excellent. While the course gets into
| pretty advanced topics that simply won't matter unless you are
| designing multi-kW systems, it covers all the fundamentals and
| builds understanding from ground up so you will know what makes
| sense to use and when.
| kleiba wrote:
| Thank you!
|
| I was just going to ask about recommended resources for getting
| into electronics. I've never been able to find anything that I
| personally found useful - often times, introductury courses are
| too basic and slow to keep me focused, or they lack exercises
| or are too theoretical, etc.
|
| There are many hobbyists who have learned all that stuff and
| can design and implement their own circuits (say, audiophiles
| or model train enthusiasts), so obviously they have all been
| able to get there. But I have never managed to learn anything
| about electronics, although I would really like to.
| progbits wrote:
| Yeah it can be hard. As a self-taught hobbyist I've found a
| mix of university courses (not whole curriculum, just pick
| and choose and don't feel bad fast-forwarding over some of
| the math theory), books (art of electronics, practical
| electronics for inventors), and high quality youtube channels
| (eevblog, phil's lab, robert feranec, microtype engineering)
| to be a good way to learn.
|
| Also eevblog forums are great. I don't post much but just
| reading through the discussions you get a lot.
|
| My greatest annoyance is the flood of very low quality
| Arduino tutorials everywhere that polute the search results.
| Not to be ungrateful, Arduino got me into the hobby, but if
| you just learned about resistors last week the world doesn't
| need your blogpost on how to connect it to a breadboard.
| Max-q wrote:
| You probably know about this already, buy in case you
| missed it: The Arts of Electronics is a wonderful book on
| electronics, starting from zero, ending up at bachelor
| level EE.
|
| I was introduced to the second edition (silver) when I
| attended college in the late 90s, and have later upgraded
| to the third edition (gold). It also has a companion book
| with more exercises and lab experiments.
|
| For everyone that wants to learn EE, it is highly
| recommend. Just beware: there are fake copies for sale on
| Amazon, so be sure you get a genuine copy.
| tzs wrote:
| The MITx version of MIT's 6.002, "Circuits and Electronics",
| is excellent. Its on MIT's OpenCourseWare [1], and on EdX
| where a session is starting today [2]. The EdX is divided
| into three parts, and that is part 1. Here are parts 2 [3]
| and 3 [4].
|
| Caveat: when I took it at EdX the textbook was available
| online for free during the course, and it is an excellent
| textbook that I found very useful. That was back when all the
| MOOC platforms weren't too worried about monetization.
|
| Now the textbook is only free online for people enrolled in
| the "verified certificate track" of the course, which is
| $189. The book is $64.97 for the paperback or DRM-free PDF
| [5]. I'm not sure how well the course works without the book.
|
| [1] https://ocw.mit.edu/courses/6-002-circuits-and-
| electronics-s...
|
| [2] https://www.edx.org/learn/circuits/massachusetts-
| institute-o...
|
| [3] https://www.edx.org/learn/circuits/massachusetts-
| institute-o...
|
| [4] https://www.edx.org/learn/electronics/massachusetts-
| institut...
|
| [5] https://shop.elsevier.com/books/foundations-of-analog-
| and-di...
| creeble wrote:
| Most of the course in link[1] is available on YouTube as
| well.
| tecleandor wrote:
| What's the starting level? My electronics knowledge is very
| basic and I'd like to start "designing" some simple power
| circuits.
|
| I know the basics of resistors, diodes, capacitors,
| transistors... And I could explain the most simple classic
| power supply: transformer, full wave rectification, capacitors
| and so on. I've built basic digital circuits (LDO + arduino/ESP
| + leds and stuff) and know some basic physics. I'm good
| soldering, though :D
| EricE wrote:
| Checkout bigclivedotcom on youtube - he reverse engineers
| circuits all the time in entertaining and accessible ways; a
| great way to learn through practical applications.
| detourdog wrote:
| MIT I think always starts from first principals. If one can
| understand and not do math that is generally enough. I have
| taken many MIT OCW classes and I'm completely uneducated.
| nraynaud wrote:
| funny, it got recently suggested to me too. I really feel like
| youtube is not individualizing the recommendations.
| hcfman wrote:
| I've been working with audio recently and found so many of the
| devices that convert 3.7V to 5V for example inject noise into the
| rail that make's it in the microphone input source.
|
| The battery support from pisource does this terribly. But so do
| many battery sources. It's not just microphones that get
| affected, but also other sensitive sensors like accelerometers.
|
| I hope that other people making DC-DC convertors put some effort
| into making sure the supply is so clean so as to prevent this in
| future.
| euroderf wrote:
| Isn't this like 95% fixable with a capacitor ? Aren't there
| cables with small embedded caps ?
| dragontamer wrote:
| Oh hell no.
|
| I think a lot of people are overly cautious of DC-DC
| conversion in this topic, but you've gone full-tilt in the
| opposite direction and are severely underestimating the
| problems that occur.
|
| 1. Its not "power-conversion" that's hard per se, its EMC
| that's very hard and not taught very well at a bachelor's
| level.
|
| 2. DC-DC Voltage Converters usually handle the entirety of
| your board's power, meaning they are the highest power
| component.
|
| 3. High power and high-frequency is a difficult EMC problem.
| This means that a bad design will absolutely send your
| electrons / energy out and radiate out like an antenna. And
| if things on the same board pick it up, it will be called
| crosstalk. And if things off-board pick it up, its called
| electromagnetic interference which almost certainly leads to
| a compliance problem.
|
| ---------------
|
| 1. Hobbyists don't care about compliance. So bam. We are
| already dealing with the biggest problem by simply not caring
| about it. (Maybe you can care and go into deeper studies,
| but... if you're a beginner just don't care. Learn this very
| difficult stuff later).
|
| 2. Prevent crosstalk by following good board design rules:
| have a 4-layer board. Use Power+Signal / GND / GND /
| Power+Signal stackup. Use two vias (one for signal-1 to
| signal-4 traversals), and a 2nd via for GND2 to GND3
| traversal of the return current). Thinking of both the
| forward current and a tightly bound reverse current is
| basically all you need to do to avoid difficult crosstalk
| problems on board.
|
| Done.
|
| Point#2 requires deeper studies than is typical in bachelor's
| level electrical engineering. But it truly isn't very
| difficult once you learn the theory. Tight ground-planes
| reduce crosstalk (and EMI problems), and furthermore thinking
| of the return-current explicitly prevents problems.
|
| Now you could have some truly difficult "ringing" from trace
| inductance and other such nasty problems... but that tends to
| occur beyond 100MHz. I'm thinking most beginners are going to
| be under 20MHz for most of their designs and thus never deal
| with those advanced "PDN" / Power Delivery Network problems.
|
| Though if you do go into PDNs, its obviously a tough subject
| with huge amounts of study and reading involved. But most of
| the problems truly are at very high frequencies and/or at EMI
| compliance. Beginner Hobbyists avoid the most difficult
| issues entirely by nature of beginner (aka: low-speed) and
| hobbyist (and therefore don't have to follow regulators).
|
| ----------
|
| I'm not a professional. But my understanding is that top-
| level EEs who work on PDNs will simulate the circuit-board
| itself to figure out trace inductances / capacitances in the
| board itself. (Closer planes of ground/power will create more
| capacitance. Long traces tend to increase trace inductance,
| etc. etc.). And tight simulations are the only way to truly
| understand the PCB and how it interacts at high frequencies
| with high-power.
|
| But such methodologies are gross overkill for a 1MHz boost
| converter with a pre-made PCB Layout, and a list of
| capacitors + inductors already picked out for you. (ex:
| https://www.microchip.com/en-us/product/mcp1640)
|
| Seriously: Page 17 (https://ww1.microchip.com/downloads/aemDo
| cuments/documents/A...) already gives you the PCB-layout you
| need for this, with recommended components. Don't overthink
| it, just copy the design from the document.
| Max-q wrote:
| We have a couple of challenges today. Hobbyists often go
| over 20MHz, because they put WiFi, BT or USB on their
| boards, giving EMC issues. Also, the speed of the modern
| ICs tend to be very high. If you have a 9600 Hz UART
| signal, that is not a 9600 Hz signal if it's a square wave
| with a modern IC with very short rise time on the pins. So
| a good old, slow serial line can with modern MCU emit noise
| up in the hundreds of MHz range.
|
| So your PCB layout tips are important, even on slow
| circuits these days.
| dragontamer wrote:
| Unless a beginner plans to sell a design on the public,
| there is no EMC (compliance) issue.
|
| Maybe EMI crosstalk. But WIFI and BT are supposed to
| eminate out like a radio and jump across boards. That's
| the point.
|
| ---------
|
| USB is a matched impedance differential pair. Are
| beginners really running high speed USB differential
| pairs down their circuits today?
|
| Because that's a really.... Erm.... strange....
| definition of a beginner. IMO anyway.
| archi42 wrote:
| Depends on your definition of beginner. It's trivial to
| put a nrf52 module (like [1]) in a PCB design and wire a
| USB socket to it; just make sure to route the data lines
| as a differential pair in kicad (add protection diodes if
| feeling fancy). And speak a little prayer that it
| actually works as intended. No need to understand what
| any of that means.
|
| Of course the notion of using such a module might be a
| step up from beginner for you, but IMHO it's more about
| the understanding. But I agree that there is no definite
| definition.
|
| Disclaimer: I'm a beginner by my definition.
|
| [1] example module:
| https://www.waveshare.com/core52840.htm
| Youden wrote:
| > Use Power+Signal / GND / GND / Power+Signal stackup.
|
| I'm just a novice (maybe intermediate) so I'm wondering:
| the common 4-layer stackups available to hobbyists seem to
| be 1oz/0.5oz/0.5oz/1oz and I assume the outer layers have
| better thermal dissipation since they're only kept from the
| air by solder mask; so wouldn't it be better to put
| power/ground on the outer layers and keep signals in the
| middle?
|
| Also maybe I'm weird and this is pointless but I typically
| put a filled copper zone tied to ground on every single
| layer, unless I have a reason to put some other kind of
| zone in a particular area. Is it necessary to have a full,
| dedicated ground plane, rather than ground + signal or
| ground + power?
| dragontamer wrote:
| Ground fill is counterproductive on the signal layer.
|
| If you accidentally get the return path on layer1 or
| layer4 instead of the designated layer2 or layer3, you've
| created noise.
|
| Power+Signal / GND / GND / Power+Signal is about
| consistency and braindead-easy tracking of return paths.
| The return path for layer1 is always layer2. The return
| path of layer4 is always layer3.
|
| Keeping track of both the forward signal (or power line)
| and the reversed return current (which was electrically
| induced onto the nearest reference plane) stops working
| if suddenly you have random reference ground-fill planes
| on the layer1 or layer4.
|
| DO NOT put GND on layer1 or layer4 if you're doing this
| methodology.
|
| ---------------
|
| Beginners likely aren't working with a hot enough circuit
| where thermal dissipation is an issue. If you do have
| thermal dissipation then I guess thermal ground on layer1
| and layer4 ties with thermal vias will be needed.
|
| In practice, the thermal resistance across the PCB cross
| section is better than beginners expect anyway. Thermal
| conductivity is just one attribute, the other attributes
| of heat movement are distance and cross sectional area.
|
| So the shape favors you up and down the PCB. Yes the
| fiberglass has worse thermal conductivity but you win on
| shape.
| aaronmdjones wrote:
| > so wouldn't it be better to put power/ground on the
| outer layers and keep signals in the middle?
|
| Signals must never cross a break or split in the plane
| they're referencing (usually 0V or ""ground""). This
| creates huge EMI problems. Your proposal would have
| signals on layer 2 crossing a split in the ground plane
| on layer 1 (that split caused by power traces).
|
| Some interesting material on the subject:
|
| https://www.youtube.com/watch?v=ZYUYOXmo9UU
|
| https://www.youtube.com/watch?v=QG0Apol-oj0
|
| https://www.youtube.com/watch?v=ySuUZEjARPY
|
| https://www.youtube.com/watch?v=0RyBCnowLsI
| dragontamer wrote:
| All of those videos are great.
|
| I'd start with this one specifically:
| https://www.youtube.com/watch?v=ySuUZEjARPY . (Your 3rd
| link).
| magicalhippo wrote:
| As the sibling comment mentions there are several aspects.
|
| You'll need proper input filtering which may require a non-
| trivial filter network. You'll also need proper output
| filtering, which does include slapping a lot of capacitors on
| there, but also careful selection of those capacitors both
| type and size. Parasitic inductance of larger packages can
| mean they can't filter high frequencies, and MLCC capacitors
| have a DC bias which means the effective capacitance is
| significantly reduced when they have a DC bias on them which
| they will have in a DC-DC converter.
|
| Then you need to take great care about component placement
| and board layout, to minimize the return path of the currents
| and such.
|
| You can skip all of that and get a board that functions as a
| DC-DC converter if you measure it with a multimeter, but
| actually be horrible. And you just can't fix bad layout by
| slapping more capacitors on there. And even with a not
| terrible layout, you can't fix it by using the wrong kind of
| capacitors. Like anything through-hole is just not gonna
| pass.
| klysm wrote:
| Making a noise-free DC-DC converter is very difficult. Any
| buck/boost style converter is going to introduce ripple and
| switching noise into the system. This is inherently
| unavoidable, and it's very sensitive to the layout of the
| board. Actively or passively filtering out all this broadband
| frequency content is far from trivial, and there is no general
| solution - only a large, high dimensional tradeoff space.
|
| You're right that noise is a concern for any analog circuitry
| though, and if you want to, you can spend a lot of money on
| specialized DC/DC converter modules with integrated inductors
| that do their best to eliminate this noise.
| exar0815 wrote:
| I do work in automotive EMC testing and it's nearly always the
| voltage conversion at fault when you fail tests or influence
| other devices.
|
| Buck-Boost converters are a noisy and finicky thing, and not easy
| to debug if you use a monolithic IC from the cheapest vendor.
| Quite annoying discussions.
| Animats wrote:
| DC-DC converters are hard, but fun. The basic concept is that
| when you put current through an inductor for a while, then
| disconnect it, you get a big voltage spike. That's a classic auto
| ignition system. You can put that spike through a diode and use
| it to charge a capacitor to get DC out. The neat thing about
| switching power supplies is that there's very little resistance
| in the power path. That's why the efficiencies are so good. The
| not-neat thing is that they are a dead short across the input for
| part of the cycle, which is why failures can cause fires and why
| you may need an inrush current limiter and/or a fuse.
|
| There are boost converters, buck converters, and ones with
| transformers. With a transformer you can isolate the input from
| the output, which is mandatory for safety if you're driving the
| thing from the AC power line.
|
| Here's one of mine. USB 5VDC in, 120 VDC out, to operate antique
| teletype machines that need 60mA 120VDC.[1] The basic circuit is
| simple, but there are multiple surface mount ferrite beads and
| small capacitors to keep the spikes from coming out via the input
| USB, output, or as RF. LTspice simulation was needed to pick the
| values for those, so as to minimize noise in both voltage and
| current.
|
| [1] https://github.com/John-
| Nagle/ttyloopdriver/blob/master/boar...
| rkagerer wrote:
| Can't you also charge up capacitors then slam them together in
| series? Is there a name for that kind of supply?
| caf wrote:
| Yes, it's called a charge pump.
|
| There's one specific sub-type called a Cockroft-Walton
| voltage amplifier.
| pfdietz wrote:
| They won the Nobel prize using this invention (which wasn't
| theirs).
|
| https://circuitcellar.com/resources/quickbits/cockcroft-
| walt...
|
| Cockcroft went on to great acclaim for "Cockcroft's Folly".
|
| https://www.bbc.com/news/uk-england-cumbria-29803990
| hakonjdjohnsen wrote:
| This is known as a charge pump, and is the third concept
| described in the linked article. The article only mention one
| flying capacitor, but you can use more than one and connect
| them in series to get a higher multiple of the input voltage.
|
| Ben Eater also did a nice introduction to charge pumps by
| building a simple one on a breadboard:
| https://www.youtube.com/watch?v=4alV5LzHLE4&t=704s
| Animats wrote:
| The high voltage version of that is called a Marx generator.
| The Museum of Science and Industry in Chicago used to have a
| million volt Marx generator made by General Electric. The
| parallel to series switching was mechanical. The "crack" when
| it fired echoed through the whole building.
|
| They've downsized to a Tesla coil.
| jrockway wrote:
| I know exactly what you're talking about! I used to go
| there so often as a kid and definitely remember the crack.
| (Also nearby was that exhibit where you could perform
| electrolysis on some water. It had a "push to start" button
| that was activated by touching some glass with a button
| outlined by a red decal. I still don't know how that
| works.)
|
| Something else stuck in my head from that museum was the
| Operation Lifesaver displays around the model train
| exhibit. I think my dad was a little freaked out by how
| many times I wanted to watch the video of the train hitting
| a car.
|
| Honestly, I'm a little disappointed every time I visit a
| museum because of how much fun I had at MSI as a kid. I
| think a lot of that was from being a kid, but ... good
| museum.
| amelius wrote:
| I see you made a current limiter from a mosfet + resistor. I
| wonder if there are ready-made components that do the same, and
| also monitor overheating. Maybe not necessary in this case
| (because you're only limiting the inrush current, not a
| continuous current). There are current-limiting diodes but as
| far as I've seen they are only available for smaller currents.
| michaelt wrote:
| You can get single-chip current limiters for LED driver
| applications. A CL2N8-G for example.
|
| In some applications you can also use almost any linear
| voltage regulator - put a resistor between your linear
| regulator's ground and output pins, and you'll get a constant
| current.
|
| Of course if your application involves the amount of power
| dissipation that requires a heatsink, you'll probably end up
| with a discrete component for that anyway :)
| amelius wrote:
| Let's say I have a voltage source of 48V, and I want to
| limit current in my system to 4.5A, precisely, and with
| overheating protection. I could be wrong but I don't think
| the led-driver and voltage regulator solutions would fall
| in this range. Also, a heatsink would not be required if
| the duration in which the current needs limiting is small.
| Animats wrote:
| Oh, you mean Q2-R5 in [1]? That was a late addition, and yes,
| it's a linear current regulator using a depletion-mode
| MOSFET. I did that because I didn't want to change the board
| layout much and it only took two components. Others have
| built this device, and having good protection circuitry means
| it works for them, not just me.
|
| Q2-R5 is not the inrush current limiter. The inrush current
| limiter is U2. That's an AP2553W6.[2] That's a part designed
| to solve a specific problem - plugging into a USB port. USB
| port ICs have overcurrent detection which will quickly turn
| off power from the port if you try to pull too much power.
| This keeps external devices from pulling down the +5 rail in
| a laptop or pad with limited power available. The port turns
| off until reset. (On Windows this used to take a reboot;
| Linux usually resets if you close and open the device.)
|
| So if you plug in something with a large filter capacitor,
| the inrush current as the capacitor charges can momentarily
| cause an overcurrent condition and shut the port down. The
| AP2553W6 has both a linear regulator and a switch. When
| everything is good, the switch is closed and power flows
| through. If there's a momentary overload, it current limits.
| If there's a steady overload, it cuts power.
|
| Devices which don't do this power startup properly are often
| the cause of problems mentioned in searches for "USB port
| stops working". Not doing this properly saves about $0.25 in
| parts cost in volume. Such devices will work fine plugged
| into a USB charger or a desktop machine, but may shut down a
| USB port on a laptop or tablet.
|
| (This is for USB-A. USB-C is more complicated.)
|
| [1] https://github.com/John-
| Nagle/ttyloopdriver/blob/master/boar...
|
| [2] https://www.diodes.com/assets/Datasheets/products_inactiv
| e_d...
| petertodd wrote:
| > The basic concept is that when you put current through an
| inductor for a while, then disconnect it, you get a big voltage
| spike.
|
| That's actually usually _not_ true, as the vast majority of DC
| to DC converters are step-down converters: you do _not_ want
| the voltage to spike. And in general, it isn 't really a
| "spike".
|
| A better way to think about what is happening is that passing a
| current from a power supply through an inductor transfers
| energy into the magnetic field. When you stop doing that, the
| magnetic field diminishes, transferring energy back into
| current. But this time, you direct the current into the
| circuit.
|
| The trick is that by picking the timing and other parameters
| correctly, you can pick the voltage of the downstream current.
| Specifically, you can do this because the _voltage_ across the
| inductor is a function of the _slope_ of the strength of the
| magnetic field around the wire in the inductor. Pick a
| different slope, and you can pick a different voltage. Since
| you usually want a stable voltage, the graph of the magnetic
| field strength will be (roughly) a sawtooth, and the graph of
| the induced voltage will be (roughly) a square wave (I am
| simplifying here for understandability!). A sawtooth shape has
| a consistent current _slope_ , which leads to a consistent
| voltage.
| Terretta wrote:
| DISCLAIMER: Described for entertainment value only. Some
| details omitted. Don't try this at home!
|
| That energy transfer makes an "interesting" party trick.
|
| Get the step up/down winding transformer from an old CRT TV.
| Get rid of other components*, and wire it with a 9 volt
| battery on one side, and connect the other with + to
| conducting surface on three sides of a box with - to the
| three opposing sides. Put a switch on the underside that
| opens the circuit.
|
| To pick up a box generally requires touching two opposite
| sides. Opening the circuit dumps the field into the person
| picking it up who gets a momentary jolt.
|
| It's enough to run through multiple people: hold hands in a
| ring of 2 - 10 people, and have two people at ends of the
| ring each press an opposite side of the box and pick it up,
| the whole ring gets the jolt!
|
| As a grade school science experiment, have the experiment
| display say something along the lines of "Guess the weight"
| so people pick up the box and get a surprise.
|
| For more about retro transformer circuits, see:
|
| https://hackaday.com/2016/07/04/retrotechtacular-dc-to-dc-
| co...
|
| This is sort of a single vibe (the switch opening) of a
| vibrator-transformer-rectifier transformer, to collapse the
| magnetic field that dumps into the still "closed" side
| through the person picking it up. No rectifier since it's not
| AC, it's just C. So the same principle, without the rest of
| the parts.
|
| * WARNING: Don't look up the rest of the owl. Don't build
| this. Don't try this. Don't let anyone touch this.
| PopAlongKid wrote:
| Way, way back, when I was in fifth grade, my dad (who was
| part owner of a car repair shop) brought an ignition coil
| (the old kind, that was connected to a distributor for the
| spark plugs) into the classroom, and I guess a 12-volt car
| battery. All 25 of us students held hands in a large circle
| and got the jolt. this was part of the teacher's ongoing
| study of electricity, which also involved winding wire
| around a hollow cardboard cylinder to make a magnetizer/de-
| magnetizer tube.
| Terretta wrote:
| Yes! And same age when my dad taught me this.
|
| (Wasn't it great learning in an age before cars had
| seatbelts, before push mowers had kill bars, and when
| nothing had warning labels?)
|
| I was mostly tongue in cheek about the danger above, as
| the most dangerous step would be relieving a previously
| functional CRT of the transformer block. The CRT
| discharge _can kill you_.
|
| Using an ignition coil should work (I didn't try it) and
| is likely safer to source if you're getting it from
| something assembled instead of from a used parts bin.
|
| As for the rest of the owl, this is from memory, nearly
| half a century ago, so, yeah, disclaimers:
|
| ---
|
| # How to Build a Prank Shock Box for a Science Exhibit
|
| This fun project will surprise your friends with a
| harmless electric shock when they pick up a prank box to
| guess its weight. Here's how you can build it and how it
| works.
|
| ## Materials:
|
| - 9-volt battery
|
| - Step-up transformer (designed to increase voltage)
|
| \\_ consider a flyback transformer from old CRT or auto
| ignition coil, talk to circuit electrician expert
|
| - Switch (spring-loaded or pressure-based)
|
| - Wires
|
| - Small box (to hold the circuit)
|
| - Electrical tape
|
| - Conductive foil or metal strips for accessible sides of
| box
|
| ## How It Works:
|
| This circuit uses a _step-up transformer coil_ to
| generate a small electric shock when someone picks up the
| box. While transformers typically work with _alternating
| current (AC)_ , here you use _direct current (DC)_ from
| the 9-volt battery. The trick happens when the circuit
| opens as the box is lifted, causing the transformer's
| magnetic field to collapse and induce a voltage spike.
|
| When the box is lifted, the switch opens, cutting off the
| current from the battery. This sudden interruption
| collapses the transformer's magnetic field, generating a
| quick, harmless jolt.
|
| ## Steps to Build:
|
| 1. _Assemble the Circuit_ :
|
| - Connect the 9-volt battery to the primary side of the
| transformer, with a switch in between. The switch should
| stay closed when the box is at rest and open when it's
| picked up.
|
| - Wire the secondary side of the transformer to two sets
| of exposed contact points on the outside of the box: one
| set connected to the positive side and the other set to
| the negative side of the transformer.
|
| 2. _Add Conductive Surfaces_ :
|
| - To make it more effective, cover _three sides or faces
| of the box_ with conductive material (like aluminum foil
| or metal strips) connected to the positive output of the
| transformer. Then cover the _opposite three sides_ with
| conductive material connected to the negative output of
| the transformer.
|
| - When someone picks up the box, their hands will
| naturally touch both a positive and negative side,
| allowing the shock to pass through them.
|
| 3. _Install the Switch_ :
|
| - Position the switch on the underside of the box so that
| it opens when the box is lifted. You can use a spring-
| loaded or pressure-based switch that triggers when the
| box is moved.
|
| 4. _Test the Circuit_ :
|
| - With the box resting, the current will flow through the
| transformer, building up a magnetic field. Once someone
| lifts the box, the circuit breaks, causing the field to
| collapse and induce the shock.
|
| 5. _Secure the Box_ :
|
| - Place and affix all the components securely inside the
| box, bringing your two wires through the sides and making
| sure the exposed contact points are positioned on
| opposite sides of the box. Tape down any loose wires.
|
| ## Science Explanation:
|
| This project uses _Faraday's Law of Induction_ , which
| states that a changing magnetic field induces voltage.
| The transformer converts the collapsing magnetic field
| into a brief, high-voltage spike, delivering a small
| shock to whatever is completing the high side circuit
| when the low side circuit is opened. Although
| transformers usually work with AC, you're using the
| moment when the DC current stops to mimic that effect.
|
| https://en.wikipedia.org/wiki/Faraday%27s_law_of_inductio
| n
|
| The conductive material on the box ensures that when
| someone lifts the box, their hands make contact with both
| the positive and negative sides, completing the circuit
| for the jolt.
|
| ## Safety Note:
|
| When done correctly, this project delivers a tiny,
| harmless jolt, similar to static electricity. Always use
| low power, an appropriate transformer, and avoid using
| higher voltages or currents. Consult with a TV repair
| expert or similar on your design before starting. DO NOT
| TOUCH ASSEMBLED CRTs. Let the TV repair person do it.
| She'll have parts anyway.
| chrisdhoover wrote:
| 7th grade shop class. We all held hands and teacher crank
| an old telephone generator
| sfilmeyer wrote:
| I initially misread this as you proposing using a car
| battery rather than a 9 volt battery, which sounds like a
| much less fun party trick.
| dheera wrote:
| > A better way to think about what is happening is that
| passing a current from a power supply through an inductor
| transfers energy into the magnetic field. When you stop doing
| that, the magnetic field diminishes, transferring energy back
| into current. But this time, you direct the current into the
| circuit.
|
| That's not my understanding of how down-converters work.
|
| Rather, there's a big fat output capacitor that the load is
| connected to, and you keep topping off its charge with a
| MOSFET gated by a feedback loop that monitors the capacitor's
| voltage and actively adjusts the PWM duty cycle to keep the
| capacitor charged at the desired voltage regardless of what
| the load does. If you your input is 100V and your desired
| output is 10V, you just keep charging a capacitor to 10V,
| disconnect when it gets to 10V, and keep repeating that at
| hundreds of kHz, faster than the load can appreciably drain
| the capacitor. Inductors and diodes are "optional", but added
| to absorb current spikes. Their main principle doesn't rely
| on induction though.
|
| Boost converters, on the other hand, rely on inductors to
| achieve higher output voltages than the input.
| kosma wrote:
| That voltage spike only applies to flyback converter. Your
| typical buck/boost converter doesn't do that - the current
| waveform is a sawtooth, and voltage ripple is designed to be in
| the mV range.
| mindslight wrote:
| DC-DC converters are not a "dead short across the input for
| part of the cycle" in normal operation - rather the voltage is
| across the inductor. If the switch stays on too long and the
| inductor reaches its saturation current, or one of the many
| other (cascading) failure modes, _then_ can you end up with
| effectively a short across the input. This can happen to many
| kinds of electronics (eg a simple tantalum decoupling cap, or
| an IC 's SCR latchup), but designing the power topology is a
| good place to think about these failure modes.
|
| (Although going 5V->120V with USB as the power source, I can
| understand how "dead short" was a decent intuition)
| Animats wrote:
| > DC-DC converters are not a "dead short across the input for
| part of the cycle" in normal operation - rather the voltage
| is across the inductor. If the switch stays on too long and
| the inductor reaches its saturation current, or one of the
| many other (cascading) failure modes, then can you end up
| with effectively a short across the input.
|
| Right. Which is why under-designed AC-line powered power
| supplies can catch fire. The failure mode of MOSFETS is
| usually to the "on" state, so the switch staying on is quite
| possible.
| retrac wrote:
| I think of it as synthesizing a sine wave (AC power) with DC
| pulses, using an inductor or capacitor for smoothing. The
| result is then rectified back to DC.
| 3dGrabber wrote:
| There exists an interesting connection between Boost Converters
| and Hydraulic Rams [1]. A Hydraulic Ram is device that can pump
| water from a stream to a higher location by harnessing the
| kinetic energy of the stream, no other power source required.
|
| The equations for the two devices are essentially the same, only
| the units change.
|
| 1 https://en.wikipedia.org/wiki/Hydraulic_ram
| agumonkey wrote:
| I love analogies between fields like this.
| nraynaud wrote:
| There is a whole area of multi-domain simulation, where the
| simulator seamlessly jumps from one form of energy to another
| as long as the units match. I have always loved that.
| agumonkey wrote:
| oh nice
| 3dGrabber wrote:
| Modelica comes to mind.
|
| https://media.springernature.com/lw685/springer-
| static/image...
|
| https://en.wikipedia.org/wiki/Modelica
| SoftTalker wrote:
| Water flows in pipes, valves, etc. concepts transfer to a lot
| of basic electrical circuits and concepts. E.g. voltage is
| analogous to pressure. Current is analogous to the volume of
| water flowing. Bigger pipe (wire) can carry more current.
| Valves are like switches or resistors. It works to de-mystify
| concepts for kids who have no concept of what electricity is
| but can think about water flowing in a pipe.
| agumonkey wrote:
| The base analogy working is cool but that other mechanisms
| on top also work similarly is what amazes me.
| ssl-3 wrote:
| Circuitry (both digital and analog, including entire
| computers) can be built using hydraulics. Complex parts
| like logic gates, oscillators are present, but also
| "passive" things like accumulators, resistors, and valves
| -- it's all there.
|
| They work in about the same way as electronic circuits
| do.
|
| (But it's almost always less expensive to push
| electricity around than it is to push liquid around, and
| the parts are a lot smaller, so obviously electronic
| circuits are the usual winner.
|
| Nonetheless, hydraulic circuits are still pretty common:
| See, for example, the valve body of an automatic
| transmission such as (mostly?) electronics-free 700R4.)
| mystified5016 wrote:
| Also the signal propagation speed in a fluid system is
| limited to the speed of sound in that fluid, vs ~c in
| electric circuits
| wrycoder wrote:
| Current is analogous to momentum, because electron drift has
| net momentum.
| mikewarot wrote:
| I've learned that the magic search word for 150ish volt boost
| converters is "Nixie".
|
| My friend needed that voltage for a Geiger counter B+ battery
| replacement.
| moffkalast wrote:
| 96% efficiency sounds great on paper for synchronous converters,
| but as SBC current draw just keeps increasing and BLDC motors can
| run at higher voltages it starts to create a major heating
| problem when you have to supply both from the same source.
|
| Something like 12V down to 5V at 5A creates a managable amount of
| heat, but going higher, 20V, 30V on the battery side and things
| start to melt all around from heat losses from that large a drop.
| In some cases I've had to resort to using cascaded rails,
| stepping first down to 24, then 24 to 12 and then 12 to 5 just to
| keep the heating spread between different buck converters even if
| it multiplies losses. Would love to hear what the expert solution
| is to this that isn't just a massive heatsink.
| mschuster91 wrote:
| > Would love to hear what the expert solution is to this that
| isn't just a massive heatsink.
|
| A smaller heatsink with active cooling and parallel MOSFETs. At
| a certain power level, it's just physically impossible to rely
| on convection cooling alone - just look at audio amps or your
| average CPU/GPU... banks of MOSFETs, caps and inductors it is.
| While the BOM part count may be higher, you need lower-
| capability parts.
|
| The danger is, you need to carefully grade and match the
| MOSFETs, otherwise you risk them failing sequentially in a very
| short time if you're operating too close to their rated current
| - one burns out, the load distributes to the others, and then
| they fail because they cannot handle the additional load (or
| one fails into dead short instead of open, which instantly
| kills all of the others).
| posterboy wrote:
| you forgot to mention it should fit under a thumbnail, probably
| moffkalast wrote:
| It would be a nice plus :P
|
| Honestly the size isn't such a big deal, as long as it
| doesn't weigh as much as two African elephants like the
| average mains PSU of this amperage.
| michaelt wrote:
| You can get 48V DC -> 5V DC 6.5A converters that are 92%
| efficient [1]
|
| You're dissipating 25W from your SBC already. You can dissipate
| the 2W from your DC-DC converter the same way.
|
| [1]
| https://www.meanwellusa.com/webapp/product/search.aspx?prod=...
| moffkalast wrote:
| > current range 0 ~ 6.5A
|
| > Fuse recommended (5A)
|
| I see they are very confident about going to 6A. These
| ratings are often just "yeah it can technically do that but
| it will reach 100 degrees during it", for any kind of stable
| continuous draw you just have to halve the rating to be safe.
| michaelt wrote:
| If you want you can buy the next size up [1] giving you 11A
| at 5V with the same 92% efficiency.
|
| Of course, it'll still dissipate the same amount of power,
| because 8% of 25W is still 2W.
|
| [1] https://www.meanwellusa.com/webapp/product/search.aspx?
| prod=...
| moffkalast wrote:
| That looks more like it (8A fuse), and relatively cheap
| on Mouser too interestingly enough. Thanks for the heads
| up I'll have to order and try one.
|
| It does puzzle me why they went with the 2.54mm pin
| layout though, those are rated for 3A max I think? So
| even if the draw is perfectly split between the two vout
| pairs they give it'll be melting at 6A already, probably
| more like 5 if not.
| michaelt wrote:
| I know the pin looks small compared to the cable you'd
| run to a wall socket for a 10A current - but those cables
| are a lot longer these copper pins, and cables are sized
| with the assumption the copper will be coated in
| insulation then coated in another layer of insulation
| then installed into a wall full of insulation.
|
| A 10mm copper pin measuring 0.6mm x 0.6mm pin would have
| half a milliohm of resistance. Even if you ran your
| entire 5A load through a single pin, it would only have
| to dissipate 13 milliwatts.
|
| I'd be more worried about the PCB traces if I were you -
| 2oz copper is only 0.07mm thick :)
| ziofill wrote:
| I'm a theoretical physicist and I swear electrical stuff is so
| hard to understand! I have a lot of respect for electrical
| engineers ^^' (and electricians)
| mglz wrote:
| For beginners it is super annoying that many tutorials say "there
| is a magical switch or oscillator here which is integral to the
| function of the boost converter, but we will not tell you how to
| actually realize it". Additionally, that needs to work at the
| voltage level you are starting out from and in many cases should
| be galvanically isolated from the converter. This is _a lot_ to
| keep in mind and it is actually not trivial.
|
| The answer here is usually to find an IC that works at your
| desired input voltage or to have a linear regulator provide a
| small amount of power for the PWM generator. Also be wary of just
| running with an AI generated answer. Claude 3.5 Sonnet suggest
| you connect an Arduino straight to 230V and after some back and
| forth generates circuits which contain strange elements like
| "antiparallel diodes" which makes no sense.
| posterboy wrote:
| sounds like a spherical cow on a frictionless plane.
| mglz wrote:
| It is a very hairy cow, which likes to bite and is stuck in
| the mud. Also it has a wierd high-frequency response. There
| is a description of tractors to get it out, but we'll skip
| how the controls work for now.
| awjlogan wrote:
| The TI Power Designer[0] is a great resource. Obviously it will
| only show you TI parts, but it's very helpful to get a base
| design. You can filter by complexity (roughly BoM count), size,
| cost etc based on the parameters (input voltage range, output
| voltage range, power etc). The designs usually have a reference
| layout as well.
|
| 0: https://webench.ti.com/power-designer/
| mglz wrote:
| Very convenient, thank you!
| londons_explore wrote:
| I have often wondered if ideas from a buck/boost converter could
| be applied to a mechanical gearbox. Voltage and current in
| electrical circuits (where voltage x current = power) is
| completely analogous to torque and speed in mechanical shafts
| (where torque * speed = power). Every electrical component has a
| physical counterpart. Spring = capacitor. Inductor = mass with
| momentum. Resistor = friction brake.
|
| The goal would be a variable ratio gearbox using a fully
| mechanical system, using a spring and a hammer type mechanism to
| convert one torque/speed to another torque/speed.
|
| This is already done in impact wrenches, but I would hope that
| rather than having an impact rate of say 5 Hz, you have an impact
| rate of 50 kHz or more, allowing a smooth conversion from one
| speed to another.
|
| Obviously, the difficulty is in the details - designing parts to
| withstand 50k hammers per second for years of operating without
| failing from fatigue.
|
| Various other mechanical things already operate at high
| mechanical frequencies. SAW filters vibrate things mechanically
| at Ghz and don't suffer fatigue failures.
| hwillis wrote:
| You're overcomplicating it; you only need a single clutch and
| in/out springs[1] to do this. If you're spinning at 4000 rpm
| and your springs cover 6 degrees of rotation, then your clutch
| needs to be able to actuate at 4000 Hz.
|
| When the clutch is engaged, the engine-side springs compress to
| supply the torque and match the speed difference. When it's
| disengaged, the springs expand back out as it returns to engine
| speed. The obvious problem is that clutches do not smoothly
| click on and off like a transistor.
|
| However there are more specialized devices that use stick-slip
| dynamics like piezo actuators. Since there is a much more rapid
| transition between "on"/"off", they can be very efficient and
| allow relatively weak devices to exert very large forces.
| They're just only able to take very small steps.
|
| [1] Labeled 4 here: https://haynes.com/en-
| gb/sites/default/files/styles/blog_lan...
| londons_explore wrote:
| > When it's disengaged, the springs expand back out as it
| returns to engine speed.
|
| What is _it_?
|
| I think you need an intermediate flywheel, with springs and
| clutches on each side. The intermediate flywheel's mass is
| tiny, so might be formed by just the masses of the springs
| and clutch mechanism.
| kbouck wrote:
| I want to power my 12V devices with USB PD. Looks like 12V is
| optional in the spec and is supported only by some devices (eg.
| UGREEN), and not by others (eg. Anker)
|
| Given a USB PD power supply which supports 15V but not 12V, and a
| usb-c/barrel-jack cable configured to negotiate for 15V, what
| would be the simplest (yet safe) circuit i could add via barrel
| jack to regulate the to voltage down to safe/consistent 12V?
|
| is a simple linear voltage regulator (LM7812) sufficient? would i
| need capacitors to smooth it out?
| klysm wrote:
| A 3V drop over an LDO is usually reasonable with low enough
| currents. Some LDOs require capacitors to be stable, and it's
| usually a good idea to have some capacitance on your power
| rails anyway.
| 15155 wrote:
| The one important thing missing from your query here is:
|
| How much current do you need?
|
| If you need, say, >100A, the possible architecture looks very
| different than ~1A or less.
| _Microft wrote:
| It might be cheaper to get a power supply that supports later
| PD standards? E.g. IKEA is selling some cheap here for either
| 8EUR (Sjoss, 1 USB-C port (max. 30W, up to 3A)) or 15EUR
| (Sjoss, 2 USB-C port (combined power output of 45W, up to 3A,
| also on a single port)). Both support PD 3.0 and PPS (that's
| the fanciest PD standard that implements requesting arbitrary
| voltages from the power supply) They also stock nice and cheap
| USB-C cables. These power supplies work fine with USB-PD
| trigger boards set to 12V.
| cushychicken wrote:
| A decent article, but there's a ton of misunderstanding in the
| comment section.
|
| For one thing: LDOs can be more efficient than buck converters,
| especially at very low current consumptions. If you're drawing
| sub 1 mA, like a battery powered system, an LDO is going to be a
| more efficient step down converter, because it doesn't have
| switching losses. Bucks are only better choices for stepping down
| voltage at higher currents because the switching losses become
| negligible.
|
| Second: a ton of people here are vastly exaggerating the
| difficulty of designing a step down buck converter. Integrated
| designs from TI or analog devices will tell you all the
| compensating components, output capacitor values, inductor
| values, etc. for common step down output voltages. Most will
| include reference layouts with a four layer six layer or even two
| layer stack up for optimal performance. It's really not that hard
| to get a one spin win out of most common buck designs.
|
| Don't be afraid. Just follow the manual. You'll be fine.
| minkles wrote:
| Lots of things in here which kill me a little:
|
| 1. You don't get a voltage spike when you disconnect an inductor.
| The field collapses and induces a current. If you measure it
| across a high impedance then it looks like a voltage spike. If
| you measure it across a low impedance then it's not necessarily
| much of a spike. Ergo depends on load impedance.
|
| 2. SMPS designs are not necessarily noisier than linear power
| supplies. It's always a design trade off. In fact you see SMPS in
| all modern RF test gear which is generally far more sensitive and
| has far more bandwidth than anything back when linear supplies
| were common. Also there is a lot of noise coming off the diodes
| in a basic bridge rectifier as well! Noise is a whole-system
| design consideration that has to be made.
|
| 3. Don't use any LLMs for designing circuits. Please go read a
| book on it designed by experts, not stuff scraped from thousands
| of idiots. I've seen some horrible stuff out there.
|
| 4. I'm sure I'll come up with more over time.
| hwillis wrote:
| > If you measure it across a high impedance then it looks like
| a voltage spike. If you measure it across a low impedance then
| it's not necessarily much of a spike.
|
| "Disconnect" implies an open circuit and high impedance.
| Workaccount2 wrote:
| This is really nit-picky.
|
| The fundamental action of a boost converter is from the
| inductors "voltage spike" behavior. The lowest noise linear
| regulator is less noisy than the lowest noise smps.
|
| I agree though that LLM's are not good at circuit design.
| thehappypm wrote:
| If you measure any voltage at low impedance, you'll suddenly
| have a massive spike of current that will blow out your
| fuses, drain your battery/capacitor/inductor, or blow your
| measurement device
| CamperBob2 wrote:
| 5. Contrary to the article, FETs don't make suitable pass
| transistors for Zener regulators that rely on Vgs being
| relatively constant, the way Vbe is with bipolars. In fact,
| even with a proper feedback loop, most FETs make awful series
| regulators due to SOA limits.
| marcodiego wrote:
| A commonly used alternative in the microcontroller world is to
| simply stack a few diodes. Very simple alternative which I have
| seen being used a few times.
| shellback3 wrote:
| Interesting, but I had expected to see a comparison of generating
| DC voltages using tubes, which were used in my university
| Electronics course, with solid state. In those days to generate a
| DC voltage from another DC voltage required generating an AC
| voltage from the DC and then rectifying it.
| stonethrowaway wrote:
| Friendly warning to people who aren't electronics savvy: this
| blog post is written in a "now draw the owl" sort of way. I'm not
| sure who the audience is. Anyone who can read this stuff at the
| level presented inherently knows most of this and then some.
| Everyone else will need a book and that book will cover this
| material as it's fairly fundamental and will derive equations
| used in here as well so you can make sense of it.
| anthomtb wrote:
| Maybe the target audience is those with lapsed circuit theory
| knowledge from undergrad and no hobby or professional power
| electronics experience afterwards? Describing myself, of course
| (most of icamtuf's stuff is up my alley, fwiw).
|
| One would think the title including "DC-DC voltage conversion"
| is enough of a squirrel-catcher to stop folks who either 1)
| Know nothing about what it means or 2) know exactly how to do
| it, from reading the article.
| dgacmu wrote:
| I've moved a lot of my home computing to home-brewed 12V UPSes
| using these. LFP charger --> Battery --> 12V or 5V DC-DC buck or
| boost/buck regulator --> device. Most UPSes are designed for high
| wattage, short runtime, but things like my firewall or small
| proxmox box for SDN+DNS benefit from low-wattage, long-runtime,
| and getting the inverter out of the picture substantially
| improves runtime. Said proxmox box uses under 10W and gets about
| 20h of runtime from a $50 battery.
| kijiki wrote:
| What charger and battery did you use?
| thehappypm wrote:
| Does it outperform a $50 UPS?
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