[HN Gopher] The magic of DC-DC voltage conversion
___________________________________________________________________
The magic of DC-DC voltage conversion
Author : zdw
Score : 103 points
Date : 2023-04-22 17:10 UTC (5 hours ago)
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| crote wrote:
| > Between the resulting thermal management issues and reduced
| battery life, linear regulation is seldom worth the pain.
|
| Rather the opposite, actually! Most simple electronics or DIY
| stuff has rather trivial needs, like USB-sourced 5V->3.3V
| conversion at a few dozen mA. A simple LDO will cost you about
| $0.01 in bulk, so your total BOM is $0.03 once you include
| capacitors. The linked CUI VXO7803-500 module is closer to $2.00.
| An LTC3240 IC will cost you $1.00, and an AP63203 IC is at least
| $0.50 too.
|
| Unless your application requires high efficiency, has significant
| voltage differences, or is handling large currents, there is no
| reason not to just throw in a dirt-cheap LDO.
| the__alchemist wrote:
| Current handling in space-constrained situations is what drives
| me from LDOs. Ie, if space-limited, linear regs top out at
| 500mA for sot23-5. So, then you need to go switching, along
| with the slew of accompanying passives.
| ejiblabahaba wrote:
| A few points:
|
| 1) LM317 and LM7805 are not LDOs. LM317 is a series regulator,
| which is way more flexible and has some infrequent but
| difficult-to-emulate use cases. LM7805 is a linear regulator
| but has substantial voltage drop relative to a modern LDO.
| Enthusiast/hobbyist space would do well to consider
| alternatives to the LM317/LM7805 if they're designing PCBs with
| surface mount components and very simple power rail needs, but
| for quick and dirty through hole designs there's few well-known
| alternatives that are truly LDOs - maybe MCP1700?
|
| 2) Enthusiast/hobbyist market isn't too sensitive to bulk
| pricing. Case in point: LM317 is about a dollar in
| hobbyist/enthusiast quantities, and LM7805 is comparable. TI
| lists 1ku TO-220 pricing at $0.65. You're definitely right for
| real products with mass manufacturing, but hobbyists don't
| generally haggle over pennies.
| Gibbon1 wrote:
| They are better than they used to be but LDO's are finickier
| than traditional NPN pass element based regulators. Unless
| you need a low drop out regulator there isn't much advantage
| to them.
|
| Tip for power supply stuff, derate the heck out of
| everything. Voltage current and power derate by 2X and you
| usually won't have issues.
| jjoonathan wrote:
| Agreed. Low-N solutions should optimize for simplicity rather
| than cost, but simplicity tends to favor LDOs too.
|
| PSA: Watch out for residual flux residue on your voltage
| dividers! I've seen parallel resistance as low as 50k. If your
| rails come up at the wrong voltage they can fry your expensive
| chips! Consider investing in packaged LDOs at the exact voltage
| you require.
| terom wrote:
| Nothing wrong with linear regulators in the appropriate
| applications. In fact, the switching converter/controller IC will
| generally include a small LDO to generate an internal Vcc supply
| for the control logic.
|
| Just don't make the basic mistake of reading the 25V maximum
| input voltage/ 1.5A maximum load current specs for an L7805 and
| thinking you can pull 1.5A at 5V from a 24V supply - it will
| quickly go up in smoke. You must understand the operating
| principals and what "thermally constrained" means.
| mastax wrote:
| For a good practical guide on switching regulator component
| selection and layout check out Phil's Lab on YouTube:
|
| https://www.youtube.com/watch?v=FqT_Ofd54fo
| https://www.youtube.com/watch?v=AmfLhT5SntE
|
| He also has good guides on digital audio processing and sensor
| fusion.
| krmblg wrote:
| His videos definitely helped demystify my prior assumptions
| about how to incorporate ESP32s or STM32 in my own custom PCB
| designs (and not deal with external programmers, castellated
| edge ICs etc or resort to devkits adding quite some vertical
| space requirements and coming with issues of their own).
|
| Highly recommended channel.
| phkahler wrote:
| If you replace the diode in a boost or buck converter with a
| second switch that is turned on and off complementary to the
| other one, they are the same circuit run in opposite directions.
| Just an observation.
| ejiblabahaba wrote:
| You can use this observation to build a "buck-boost" topology
| that can make the output voltage larger or smaller than the
| input voltage. This is common for 1sNp Li-ion batteries that
| need a high-current 3.3V rail - buck from 4.2V to 3.3V at full
| charge, boost from 3V to 3.3V at low charge.
|
| There's actually a bunch of ways to make buck-boost style
| converters that can do both functions, like the cuk and sepic
| topologies. There's also bidirectional bridge converters that
| can change input and output direction - you see this a lot on
| hybrid vehicles (12V to 48V or vice versa) and electric
| vehicles (48V to 400V and vice versa).
| osigurdson wrote:
| I always liked the switched capacitor concept.
| jacquesm wrote:
| Indeed. The first time I ran into the MAX233 I really did a
| double take. How on earth does it do away with all of the
| supply voltages?
| stametseater wrote:
| I'm not sure if it's a good analogy, but I think of boost
| converters like hydraulic ram pumps, which convert high flow low
| pressure water into low flow, high pressure.
| mastax wrote:
| I spent a long time afraid of making switching regulators because
| I heard so much about how complicated they are, failure modes,
| EMI problems, etc. But when I got over that I never had any
| problems just reading and following the datasheet
| recommendations. The layout rules aren't even particularly
| complex and the datasheets will always give you an example layout
| to copy anyway.
|
| Of course once I figured that out I found self-contained
| switching regulator modules like the RECOM R78-K and RPM series
| which are foolproof and cheap. Well the RPM modules were cheap at
| the time, but apparently they've doubled in price. Maybe that was
| an introductory thing or the supply chain got to them.
| ejiblabahaba wrote:
| During a college internship, I actually debugged an EEPROM
| corruption issue on a PLC card all the way back to the power
| supply the original designer had copy-pasted out of the
| datasheet. The compensation network they had used was
| definitely not stable, even though it was exactly the same
| input and output voltages and circuit elements in their diagram
| and our application.
|
| I've written my fair share of datasheets now, and while most of
| us are trying to do a good job and be clear and helpful,
| sometimes the stuff below the spec tables in the datasheet is,
| uh... less good than we'd like, for any number of reasons
| (inexperience, no time, someone left halfway through writing
| the datasheet, someone forgot to clean up copy-paste from the
| other datasheet with the slightly different thing, etc). I
| guess my point is: trust, but verify.
| mikewarot wrote:
| I was helping a friend repair some _old_ (WW2 vintage)
| transmitting gear. The voltage dividers used to bias the tubes
| used almost 100 watts by themselves! Quite the contrast to modern
| electronics.
| perlgeek wrote:
| Just the other day I idly wondered how LED "light bulbs" regulate
| down their 230V (here in central Europe, at least) to the ~2V
| needed per LED.
|
| Although it's from a different starting point (AC, not DC), after
| reading the article it seems they could use an AC->DC converter
| and then a charge pump.
|
| Is that what they actually use? Or is there something
| easier/cleverer when starting from AC?
| NikkiA wrote:
| LED bulbs usually use the most basic of power supplies, the
| capacitive dropper[0], the downside is that they tend to die
| easily.
|
| Also, the LED diodes themselves will often be multiple in
| series (a string), or series-parallel (several strings in
| parallel) depending on the bulb, that end up needing more than
| just 2V, anywhere from 12V to 60V or so per string of diodes.
|
| Sometimes the high power diodes being used are themselves a
| series chain of diodes on a singular piece of silicon encased
| in a blob of phosphor, so that the diode package ends up
| needing 12V or so. These are often referred to as 'COB' diodes.
|
| (apologies for the RAS syndrome, but saying 'LE diodes' or just
| 'LED' to refer to the individual light elements when talking
| about 'LED bulbs' is too confusing otherwise)
|
| [0] https://en.wikipedia.org/wiki/Capacitive_power_supply
| wrenzh wrote:
| For household LED bulbs almost always Flyback.
| toast0 wrote:
| They probably have a switching power supply, but if you want
| really simple and low parts count, you'd do a transfomer down
| to something nicer, have a full bridge rectifier, a capacitor,
| a current limiting resistor, and then put all the leds in the
| bulb in series; that way you don't need a big ratio for the
| transfomer... although maybe that's not a big deal, and you may
| prefer to not need a higher voltage capacitor, or a more
| failure tolerant parallel wired LEDs. You could have a linear
| regulator in there too, but careful component choices may allow
| that to be omitted.
|
| But switch mode power supplies are probably more efficient and
| highly miniturized, better adapted to different line voltages,
| etc. All around a better choice. Some sort of smarts are needed
| to work well with dimmers as well.
| VLM wrote:
| The proper way to select linear vs switched is really a flow
| chart of some applications require super low analog noise or low
| quiescent current and cannot tolerate a switcher solution. The
| next step is a complete system analysis including power/battery
| budget AND thermal for both solutions then pick the overall
| system level winner. No point in spending dollars of switcher
| components to save fractions of a penny of battery energy.
|
| Another interesting point is its "generally" easier to buy/build
| constant current linear sources than constant current switching
| sources. Plenty of sensor applications where you want to mostly
| just limit to 4-20 mA or similar.
|
| Final point to make is "generally" with massive hand waving and
| isolated exceptions, linear sources are harder to destroy via
| inductive loads and oscillating loads and ESD / EMI impacts.
| hgomersall wrote:
| As someone that works with low noise systems but on the
| firmware/software side, is it possible to design a low noise
| power supply with a switcher, without some kind of linear stage
| (like a final LDO regulator)? The hardware engineers are good,
| but I'd like to understand this a bit myself.
| ejiblabahaba wrote:
| In principle yes, in practice it's rarely worth the cost and
| complexity.
|
| If you're careful about the converter design (keep the high-
| current loops extremely short, use counter-rotating loops to
| tightly confine magnetic field within those short loops, use
| a soft-switching topology to reduce EMI and sharp edges at
| the switch node, switch quickly or use multiple parallel
| converters at different phase offsets to reduce magnitude of
| current ripple), you can get decently low noise. There's a
| good Jim Williams app note about this.[0]
|
| But it's almost never worth it to do this, since there's LDOs
| with two or three orders of magnitude better noise voltage.
| There's a time and a place for a really low noise converter;
| usually EMI constrained galvanically isolated converters like
| medical supplies or scientific instruments need them and
| aren't too sensitive to the cost or development effort. But
| even then, you'll often find LDOs cascaded on the outputs
| just afterward, since a good LDO can add another two orders
| of magnitude of ripple rejection in the switching frequency
| band.
|
| [0] https://www.analog.com/media/en/technical-
| documentation/appl...
| PragmaticPulp wrote:
| > The proper way to select linear vs switched is really a flow
| chart of some applications require super low analog noise or
| low quiescent current and cannot tolerate a switcher solution.
|
| Switching pre-regulators followed by a high PSRR LDO with some
| filtering can work here
| bilsbie wrote:
| What's the best way to boost a dc voltage really high like into
| the mega volts?
| hasmanean wrote:
| For megavolts just rub some cats fur over an ebony rod.
|
| Megavolts.
|
| Aka static electricity.
| bilsbie wrote:
| How does the boost converter mentioned here work? I'm not
| understanding the explanation.
| mordae wrote:
| You really need to design it yourself to grok it. It's weird.
| Try using Falstad's online simulator.
| ejiblabahaba wrote:
| Step 1: You briefly short the inductor. Inductors cannot
| instantaneously change current, so they will linearly ramp up
| the current over time. This builds up a magnetic field in the
| inductor.
|
| Step 2: Stop shorting the inductor. Inductors cannot
| instantaneously change current, so the now-built-up magnetic
| field continues pushing current into the switching node. The
| magnetic field and the inductor current linearly ramp down over
| time.
|
| The forced current will push charge onto the parasitic
| capacitance of the switch (from switch to ground), the inductor
| itself (from inductor output to inductor input), and the
| reverse diode capacitance (anode to cathode).
|
| Since capacitor voltage is charge over capacitance, once enough
| charge is forced onto the capacitance at the switch node,
| eventually the voltage from the switch node to the output
| capacitance is high enough to turn the diode on in forward
| conduction. The rest of the inductor current is forced into the
| output capacitance until the remaining magnetic field in the
| inductor is depleted.
|
| Step 3) Repeat very fast to reduce inductor size and ripple
| current required (100s of kHz or MHz speed). Vary the duration
| for which the inductor is shorted in step 1 according to how
| much charge you need to put on the output capacitor. You could
| figure this out open-loop by noting that output current at the
| high voltage side is in charge per second, output voltage is
| equal to charge over output capacitance, calculating the time
| taken for the ramp to grow and decay, etc. Or you could design
| a closed loop control scheme that looks at the output voltage
| and converts it to shorted duration for you (this is what most
| integrated circuit boost converters do).
|
| In summary, you dump current into a inductor to build up a
| magnetic field, then you use the inductor's magnetic field to
| yeet current up over a large voltage difference.
| SigmundA wrote:
| I know how boost converters work but reading your great
| explanation made me realize how similar they are to an impact
| wrench. Ever wonder how an impact wrench creates such massive
| torque?
|
| Spin up a fly wheel then let it hit the dogs greatly
| amplifying the torque through stored kinetic energy similar
| to an inductor being dumped.
|
| https://www.youtube.com/watch?v=xQzqNnWG21s
|
| I always like how electricity can be compared to mechanical
| and hydraulic systems, it's not always perfect but there is
| obviously a lot of overlap between voltage, current,
| pressure, flow, torque and rpm. Power is the common thread.
| Animats wrote:
| I designed a DC-DC converter once.[1] This is an exotic
| application - providing 60mA Teletype signals at up to 120VDC,
| with power from a 5V USB port.
|
| There are two main trouble spots in DC-DC converter design -
| protection and noise.
|
| A switching power supply is a dead short across its input once
| the inductor has saturated. The switch, usually a power MOSFET,
| needs to turn off on every cycle before that happens. Otherwise,
| something will fail and probably burn out. Also, the failure mode
| of power MOSFETS is usually "on". So protection circuitry is
| needed. Fuses, current limiters, etc. This is why UL approval for
| switchers connected to the power line is important.
|
| Switchers work by generating big inductive spikes. Those spikes
| are supposed to be directed into capacitors and smoothed out into
| DC. Without suitable filtering, spikes will be pushed into the
| power source, the load, and the RF spectrum. A few ferrite beads,
| Zener diodes, and small capacitors in the right spots will fix
| this. LTSpice simulation is useful in picking the component
| values. You're not done until both the current and voltage curves
| are flat.
|
| [1] https://github.com/John-Nagle/ttyloopdriver
| azubinski wrote:
| Oh yes, elementary physics course is full of magic...
| jacquesm wrote:
| I'd be really interested in a teardown of what goes into a modern
| tri-phase solar inverter.
| ejiblabahaba wrote:
| There's not much to it. There's usually some stage-1 converters
| at a subnetwork of panels that step the panel voltage up to a
| common DC bus voltage with all the MPPT and relevant
| OTP/OVP/UVP/OCP/etc. Then the big DC bus gets combined across
| all panels and fed into a three phase inverter with IGBTs or
| sometimes SiC FETs (getting more common), which just looks like
| a hex bridge across a three phase transformer. There's gate
| drivers (maybe isolated), amps for current and voltage sensing
| (maybe isolated), some protection circuits, and a half-assed
| flyback to run the fans and the control DSP. Some models might
| host an MCU for data logging and comms out to a control plane.
|
| There's a handful of projects where the size of the solar field
| is large enough to make it economic to step up from 400V or
| 800V bus. I've seen many 1000V buses, a few 1200V and 1500V
| buses. Honestly it's exactly the same circuits, just with
| higher voltage ratings; all your switching elements are still
| giant hockey pucks, you're still doing a three phase hex
| bridge, etc. The half-assed flyback is sometimes replaced with
| something a little less braindead.
| jacquesm wrote:
| When I was 17 or so I built a simple inverter out of a big
| 12V transformer and some 3055's (RCA's, not Motorola) which
| was enough to run most of my gear when it was 'lights out'
| (or not...). So I understand the basics. But those
| transformerless sine wave inverters are interesting, they
| seem to get away with squeezing a 20 KW inverter into a
| relatively modest package at a ridiculously high efficiency.
|
| On top of that they have to comply with a whole host of
| safety regulations, so even if the theoretical block diagram
| is as simple as you've outlined it the actual implementation
| is likely going to be a lot more complex and interesting.
|
| Any pointers to where I can dig around without opening one up
| myself would be greatly appreciated, most of the youtube
| stuff is for very cheap or small gear.
| mordae wrote:
| > The deal with linear regulators is that despite what some
| internet sources might recommend, you probably shouldn't be using
| them in your designs.
|
| Yeah, no.
|
| 1. Linear regulators do not introduce voltage ripple and by the
| nature of being variable resistors, they form a nice low-pass
| filter with the capacitors around it. For some sensitive designs,
| you use a switching converter to step down voltage to e.g. 5V,
| filter it and then use LDO to get it down to 3.3V with even more
| filtering.
|
| 2. Linear regulators are dirt cheap. And for e.g. USB devices
| drawing less than couple hundred mA @ 5V using a regulator to
| step it down to 3.3V would be an overkill.
|
| Granted, recent Raspberry Pi Pico (for example) does use a
| switching regulator (unlike other boards in that form factor),
| but it also has led to complications with power supply ripple
| showing in ADC readings.
|
| But sure, if you application needs higher efficiency, steps down
| by more than ~2V or pushes around a lot of current, switching
| regulator is a better choice.
| bsder wrote:
| And if your device spends a lot of time _asleep_ , linear
| regulators may beat switching regulators by a _LOT_.
|
| Leakage current can dominate your design, and switching
| regulators often have lousy leakage current specs (to be fair,
| so do a lot of old school linear regulators). Furthermore,
| switching regulators often have to "spin up" while a linear
| regulator is just sitting there ready to go as soon as your MCU
| switches on.
|
| In addition, switching regulators tend to be designed for
| higher currents and tend to have _terrible_ efficiency at small
| currents ( < 1mA). If your circuit uses a very small amount of
| current even when active, a linear regulator may be superior
| even for constant-on systems.
| ejiblabahaba wrote:
| Nowadays you can pretty easily find switchers with sub-100nA
| quiescent current + leakage, e.g. TPS62840 (of course, that's
| assuming you're at room temperature... FETs at high
| temperature are all crap for leakage). I note you get 80%
| efficiency at 1uA out on this device with a 3.6V to 1.8V
| stepdown config; beats the LDO by a lot, particularly if you
| spend a lot of your time at uA load currents.
|
| But spin-up time... Yeah that still sucks :)
| 15155 wrote:
| One can purchase $0.15 TI parts have <0.4mA quiescent current
| and output 3A. These things draw so little under no/low load
| circumstances that my cheaper 4-digit readout benchtop
| supplies cannot detect any draw.
|
| https://www.ti.com/lit/ds/symlink/tps563201.pdf
| otherjason wrote:
| 0.4 mA quiescent current is _huge_ for very low-power
| designs though. If your system must spend the majority of
| its time consuming very little power, that level of
| constant current draw is a non-starter.
| bsder wrote:
| 400uA isn't "low"--that's roughly speaking a fully-awake
| MCU running at 10MHz.
| mschuster91 wrote:
| There is one case that's missing: variable input, say a USB-C PD
| powered device that can use anything from 5-20V despite operating
| internally at 12V (which, iirc, most laptops do), or automotive
| devices that can run at anything from 6V (motorbike) to 24V
| (truck, bus) while being tolerant of >100V spikes during load
| changes.
|
| How do these work?
| algo_trader wrote:
| Are DC-DC convertors applicable for high-power industrial
| applications?
|
| Can a mega pack battery output be converted 10kVDC without an AC
| step ?
| tonmoy wrote:
| As far as I have heard modern power electronics is
| sophisticated enough to do that
| ejiblabahaba wrote:
| This is absolutely something you could do, in the sense that no
| one in electrical engineering will raise an eyebrow if you call
| your DC-DC conversion with an "AC" step in the middle a DC-DC
| converter. There's fundamentally going to be alternating
| currents in any DC-DC design, but typically at the inputs and
| outputs it looks like an average DC current with a small amount
| of AC ripple.
|
| The kind of DC-DC converters that work well for megabattery to
| 10kVDC conversion will look very different from the kind of DC-
| DC converters that step up your 3.3V rail to 5V for some low-
| power peripheral, and may actually have individual components
| that completely reverse current direction for more efficient
| current transfer. You pretty much need a transformer to handle
| the high power transfer and voltage ratio mismatch. Depending
| on the pack voltage you might use multiple stages cascaded, but
| typical 400V-800V packs can step up to 10kV in a reasonable
| number of turns (12-25). The battery pack side probably has
| IGBTs or SiC FETs driving some kind of large bridge switcher
| (or several parallel bridges); the 10kV side probably has some
| big chonker diodes in a rectifier bridge, though they
| conceptually could be replaced with synchronous switches if you
| could find thyristors with fast enough switching speed and
| better efficiency (usually it's not worth it). Technically this
| topology runs the transformer primary current in both
| directions (hence the rectifier at the output) so I guess this
| is the "AC" stage in the middle... But it's worth pointing out
| that the AC portion is incidental to operation, unlike
| something like a Tesla power wall using an AC inverter to feed
| power into the AC grid, and a grid-connected charger converting
| that back to DC.
| cellularmitosis wrote:
| Yes, though at that voltage range you'll need to stray into
| somewhat esoteric parts, like silicon carbide mosfets / igbt's
| https://www.power-mag.com/pdf/feature_pdf/1461163294_Woifspe...
| nunuvit wrote:
| Haha SiC and IGBTs are hardly esoteric. If anything, GaN is
| esoteric. You just wouldn't know it because industrial
| doesn't get the same press as computer power supplies.
| cellularmitosis wrote:
| Thanks! Just a hobbyist, glad to hear industry perspective
| on this!
| algo_trader wrote:
| x10 for this link!
| jacquesm wrote:
| Check out the hardware involved in HVDC transmission lines to
| get an idea of what 'high power DC' looks like.
| VLM wrote:
| "can" yes.
|
| Industrially, no. You're asking for an automotive ignition
| without a coil, pretty much not done.
|
| Various logic chopping options exist to be technically correct.
| If you define a pulse as not being "AC" because its not a
| constant waveform or its not wall outlet 50 hz or 60 hz, then
| sorta kinda thats an engine ignition coil. If you define a
| tesla coil as not being AC because its a resonant ckt with a
| quarter wave antenna colocated, then sorta kinda sure no AC.
| kwantam wrote:
| Yes, dc/dc conversion is definitely applicable in high-power
| applications. As one example, high-voltage DC power
| transmission [1] is in widespread use globally, and always
| requires a dc/dc conversion step for connection to local grids.
| In addition to dc/dc conversion during transmission, converting
| from DC to AC (known as _inversion_ ) uses essentially the same
| techniques.
|
| To answer your question more directly: stepping a battery's
| output to 10 kV is a good example of an application that would
| almost always be done with a dc/dc converter in an industrial
| application.
|
| (Aside: "without an AC step" is slightly tricky. If by AC you
| mean 50 or 60 Hz, definitely can and should be avoided. But AC
| is generally used to refer to any non-constant voltage or
| current, and if that's what you mean then the answer is no
| since a dc/dc converter works by switching, which by definition
| means there's some sinusoidal voltage somewhere in the
| circuit.)
|
| (Source: I used to design integrated circuits for industrial
| control.)
|
| [1] https://en.wikipedia.org/wiki/High-voltage_direct_current
| algo_trader wrote:
| > almost always be done with a dc/dc converter in an
| industrial application.
|
| thanks. lots of good details in this thread.
|
| > if by AC you mean 50 or 60 Hz, definitely can and should be
| avoided.
|
| Yes, i meant avoiding the maintenance and losses of an actual
| transformer
| amelius wrote:
| How much energy would we save if we replaced all linear
| regulators by switched configurations?
| johnea wrote:
| Already done in most electronics...
| kec wrote:
| Largely done except when it can't be due to noise / expense /
| reliability.
| johnea wrote:
| The "magic" of course, is AC...
| magicalhippo wrote:
| Not really. AC literally stands for alternating current,
| meaning the current flows the other direction in the conductors
| as well. That's not what happens in most DC-DC converters.
| Instead the current is switched on or off (or this way and that
| way if you prefer).
|
| As a visualization, the hydraulic ram pump[1] is the water
| equivalent of a DC boost converter[2]. At no point in the cycle
| does the water flow in reverse. Same with the DC boost
| converter.
|
| [1]: https://en.wikipedia.org/wiki/Hydraulic_ram
|
| [2]: https://en.wikipedia.org/wiki/Boost_converter
| ejiblabahaba wrote:
| Technically all DC-DC converters at a minimum have an AC
| current in their input and output capacitances. Since we see
| a small ripple voltage across the capacitors, it must be true
| that the direction of the current flowing in the capacitors
| is alternating.
|
| It is true that in most cases the inductor current isn't
| changing direction though.
| labster wrote:
| Nice try, Nikola, but AC is too dangerous.
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(page generated 2023-04-22 23:00 UTC)