[HN Gopher] Teardown of a PC Power Supply
___________________________________________________________________
Teardown of a PC Power Supply
Author : parsecs
Score : 198 points
Date : 2021-05-23 16:55 UTC (6 hours ago)
(HTM) web link (www.righto.com)
(TXT) w3m dump (www.righto.com)
| guenthert wrote:
| The description of the regulation of the 3V3 circuit is IMHO
| misleading. The inductor isn't a magnetic amplifier (multiple
| coils would be needed), but rather a filter element.
| kens wrote:
| Are you familiar with the use of magnetic amplifiers to
| regulate 3.3 V outputs? I traced the circuit and it's a
| magnetic amplifier. The same winding is used for control and
| output, as is typical in power supplies.
| chmaynard wrote:
| A related article was recently posted on HN:
|
| https://spectrum.ieee.org/computing/hardware/a-half-century-...
|
| https://news.ycombinator.com/item?id=27257448
| nickpeterson wrote:
| Just an observation from years building computers. Never cheap
| out on power supplies. Always buy one (don't use one included in
| a case), and buy one rated 25-30% above what you think you'll
| need. Some of the most aggravating troubleshooting you'll ever
| endure can be avoided entirely.
| bcassedy wrote:
| What sorts of problems are caused by power supply issues?
| monocasa wrote:
| Towards that end does anyone know if there any ATX power
| supplies that will stream out their sensor info over a serial
| port or something?
|
| It'd be nice to have power monitoring on that side of the
| mainboard's power regulators and caps, to pick up marginal
| issues before they get filtered out, and the power supplies
| these days will have a little ucontroller with all that
| information anyway without the mainboard having to duplicate
| that monitoring circuitry in the right place.
|
| For what's such an important piece of a computer there's so
| little introspection for data while in use that has to be being
| collected regardless. Yeah, you can always hook up a oscope or
| what have you, but catching it in the act of being marginal
| early on would have saved me more hours in my life than I'd
| like to admit.
| daper wrote:
| Server PSUs support such communication (looks like this is
| PMBus protocol, variation of SMBus, which is variation of
| I2C). In servers it's connected to the BCM and usually allows
| to read input and output power, FAN speed, temperatures and
| status (good/bad). The BCM often records historical data,
| including peak power (in last 1h, 24h), etc.
|
| After quick searching is looks there are people reading this
| info with a MCU [1]. But I think it would be hard to find
| such PSU in ATX form factor.
|
| [1] https://github.com/sxjack/dps750tb_psu_i2c
| jlgaddis wrote:
| IIRC, Corsair's AXi and HXi series power supplies --
| basically, the really expensive ones! -- support PMBus (I2C).
|
| The entry-level and lower-priced ones don't, AFAIK.
| jrockway wrote:
| I had a Corsair power supply with this feature. The system I
| built with it was quite flaky, but I could reproduce the
| failure and eventually debugged a 12V transient dropout (when
| running AVX workloads) that was the cause of the flakiness.
| The built-in monitoring didn't help at all; doesn't update
| frequently enough, and the computer crashed by the next USB
| polling cycle anyway. I used an oscilloscope.
|
| I don't really have enough data to outright blame the power
| supply. I don't think I connected all of the 12V lines to the
| motherboard (power supply didn't come with enough cables),
| and I can't be sure that the motherboard was designed
| properly for a mildly-overclocked 6950X (VRM banks,
| capacitors near the CPU, etc.)
|
| It was all enough of a pain that I will never buy another
| Corsair power supply. My current best practices involve only
| buying Seasonic power supplies, and connecting every possible
| "optional" power connector to the motherboard. If the PSU
| doesn't come with enough cables to do that, buy them
| separately. My current Threadripper motherboard has a 6-pin
| and 2 4-pin ATX12V connectors, and a Molex connector. Many
| are marked "optional" in the motherboard's instruction
| manual, but I have them connected anyway. Probably overkill.
| Great stability. Without having designed the system or the
| test scenario, skipping optional things sounds like the sort
| of thing that's going to cost you a lot of time at some
| random point in the future. Best to avoid, even if you look
| like an idiot to the EE that designed the board.
| dendriti wrote:
| Whenever I experience issues which are likely related to a
| power supply, it is much easier to drop in a known-good
| replacement than to spend time diagnosing the specific
| issues. Also better to remove a potentially faulty PSU before
| it damages much more expensive hardware.
| monocasa wrote:
| The typical failure modes mean that it'll be marginal for a
| while, and should be able to give you information before it
| goes fully bad. Being able to have introspection before it
| goes fully bad is what I want, as I hope to have some data
| before it even makes it's way on to a bench.
|
| The power clients (mainboard, GPUs, disk drives, etc)
| normally know they're getting pretty bad power from a PSU
| and filter it heavily to smooth it out. It'd be nice to
| know if the voltage is occasionally dropping and it's just
| being covered up by downstream caps that are over
| provisioned to just smooth out not fully rectified AC.
| TwoBit wrote:
| How do you tell a quality power supply?
| faeyanpiraat wrote:
| You can't.
|
| Even quality brands have crappy models.
|
| They are not necessarily the cheapest ones, it is possible
| that the 400w is fine, the 550w is crap, and the 600w is fine
| again, even if they are in the same series.
|
| They can also change the specs over time, without any
| indication on the packaging.
|
| You have to look for reviews where they actually disassemble
| and check the insides of the psu to determine if it is a good
| buy.
|
| There is a forum local to my language where they keep track
| of the small number of truly recommended models, there must
| be an English equivalent.
| ZekeSulastin wrote:
| Probably the closest thing would be the PSU tier list from
| the LTT forums:
| https://linustechtips.com/topic/1116640-psucultists-psu-
| tier... but even then it's based on aggregated reviews etc.
| toast0 wrote:
| The 80plus sticker program doesn't mean a lot, but it does
| mean a little. Being from a brand that's been around for a
| long time and is not known for cutting all the corners helps
| too.
| flyinghamster wrote:
| I learned "what not to do" from my work experience, having to
| wrangle machines with cheap PSUs, and at home having a
| "supplied with the case" PSU say "pop" to me years ago. Get
| something good, and you won't have to get it twice.
|
| But they don't last forever, and my old file server's 10-year-
| old PSU finally started causing random errors about a couple of
| months ago - recognized when a sustained hard disk operation
| dimmed the power LED. I had spares, but it's time for me to
| think about building something new. Whether it's more computing
| power for the same electrical input, or the same for less, I
| can do better.
| walrus01 wrote:
| If anyone wants to see a really top quality PC power supply, for
| comparison to a cheap one, take a look at the board and layout on
| a $100 seasonic power supply. Well known Taiwanese power supply
| company that doesn't try to compete on cheap prices and has been
| around for 20+ years.
| cesarb wrote:
| > The secondary circuitry produces the four output voltages: 5
| volts, 12 volts, -12 volts, and 3.3 volts. [...] The power supply
| also provides a negative voltage output (-12 V). This voltage is
| mostly obsolete, but was used to power serial ports and PCI
| slots.
|
| And even older PC power supplies also provided a -5V voltage, the
| corresponding pin on the ATX connector is now (according to
| Wikipedia) a reserved pin.
|
| This progression also shows in the expansion slot standards: the
| ISA slot had pins for -5V and -12V; the PCI slot removed the -5V
| pin; and the PCIe slot finally removed the -12V pin. That is, a
| motherboard without any ISA or PCI slot, and without a RS232
| socket or header, has no use for the -12V voltage.
|
| And there's already a newer power supply standard, called
| ATX12VO, which simplifies the power supply by providing only 12V
| (and a separate standby 12V). There's already at least one
| motherboard built for that standard:
| https://www.anandtech.com/show/15763/first-atx12vo-consumer-...
| bruce343434 wrote:
| > -12v, -5v
|
| What prevents one from just wiring mobo.5v to port.gnd and
| mobo.gnd to port.-5v? That would effectively create a -5v
| potential between port.gnd and port.-5v
| dmytroi wrote:
| That would create a floating ground, and systems needs to be
| designed for it. Because likely motherboard ground is
| connected to chassis, and it connected to earth, while power
| supply most likely have it's own ground connected to earth.
| formerly_proven wrote:
| -12 V was used for RS-232, which uses +12 V and -12 V levels
| (with a very wide tolerance band). Having a separate supply
| for this was a design decision which was pretty much
| instantly obsolete with integrated charge pumps: All RS-232
| outputs are running off of charge pumps running at (-2) and
| (+2) ratios, so +-10 V levels with a 5 V supply.
|
| I don't know what -5 V was used for. Maybe some analog
| circuits somewhere, very early MOS logic also often had
| awkward supply voltages (charge-pumps made this obsolete too,
| just like high-voltage supplies for EEPROMs).
| kens wrote:
| Early DRAM chips like the MK4116 required -5 V, +5 V, and
| +12 V. (-5 was the substrate back bias for the chip.) So
| the ISA standard required -12 V, -5 V, +5 V, and +12 V.
| toast0 wrote:
| -5v was often used in sound cards for audio amps, I
| believe. I've got an arcade machine with an AT supply that
| uses -5v for the audio amp anyway.
| jlgaddis wrote:
| I just recently made a nice little 3.3V, 5V, and 12V power supply
| for my electronics bench using the power supply from an old
| server.
|
| Saved me from buying one _and_ kept the power supply from ending
| up getting throwed out.
|
| "Win-win", as my annoying ex-boss would say.
| Prcmaker wrote:
| That's exactly what I did for my first benchtop supply. Being a
| student, 'free' was a pretty good deal. Used it regularly for a
| good many years until one project I had drew so much current it
| really accentuated the voltage ripple.
| dhdc wrote:
| Be careful though, ATX power supplies don't have a crucial
| feature that bench supplies do: setable current limits. They
| will pump out as much power as they can to maintain the output
| voltages until they saturates.
|
| Which can result from releasing some magic smoke if you are
| lucky, to a call with your insurance company.
| Gys wrote:
| I am pleasantly suprised this does not have its own internet
| connected microcontroller. So at least one element that is still
| not hackable.
| BenjiWiebe wrote:
| Internet connected microcontrollers weren't very common in
| 2005.
| Gys wrote:
| Ai, missed that part! Thanks.
| Animats wrote:
| Some components, mostly capacitors, have the wrong hole spacing
| for their pins, and leads were bent to fit. That suggests part
| substitutions during assembly. Many of the through-hole
| components were not pushed all the way down into the board. That
| suggests overworked assemblers. This was obviously hand-
| assembled.
|
| The author makes a point that there's a clear division between
| the AC line side and the DC side. That's required for UL
| approval, but power supplies do show up without it. The power
| transformer that crosses the boundary should also have a split
| bobbin, so the AC line side coil and the output side coil are
| separated by a barrier, not wound on the same bobbin.
|
| There are worse power supplies.[1]
|
| [1] https://linustechtips.com/topic/515473-teardown-and-
| review-o...
| ta988 wrote:
| Sometimes you put the resistors above the PCB to facilitate
| heat exchange with air cooling.
| lmilcin wrote:
| > The power transformer that crosses the boundary should also
| have a split bobbin, so the AC line side coil and the output
| side coil are separated by a barrier, not wound on the same
| bobbin.
|
| Separate bobbin is not required for robust isolation.
|
| For example, just right now on my bench there is a medical
| separation transformer. No separate bobbin (hint: it is
| toroidal).
| formerly_proven wrote:
| I have never seen a split bobbin in an ATX supply -- they are
| bad for efficiency.
| arkh wrote:
| Years ago, Canard PC Hardware (a French magazine) tested some
| low budget PSU:
| http://www.x86-secret.com/dossier-36-3000-Alimentation_Nonam...
| their conclusion was to not put those in any PC if you value
| your other components and maybe your home (lot of fireworks
| under mild load: https://youtu.be/f6snWfd1v7M?t=60 )
|
| One of the constructors attacked them and lost.
| GekkePrutser wrote:
| There's worse power supplies sure but this one is still a mess.
| I don't see anything obviously dangerous but it's still a dirty
| ugly design and assembly. Other companies like Delta
| Electronics manage to cram lots of components in small spaces
| too but they actually do a good, clean job.
|
| Most PCBs with large, heavy through-hole components are still
| manufactured by hand, by the way.
| [deleted]
| TwoBit wrote:
| Well he was destroying a power supply to make this report and
| so maybe there was a budget.
| bonoboTP wrote:
| Even if you're a "computer person" who is comfortable messing
| with the internals of a PC, be very careful with the power
| supply. Opening it up should really be left to professionals.
| Capacitors can remain charged for a long time after disconnecting
| the power cord. If despite all the warnings, you open it up to
| fiddle with internals because you think you understand the
| components and can pay attention not to touch things, at the very
| least, use only one hand at a time to avoid creating a circuit
| through your heart.
|
| In most other parts of the computer the worst that can happen in
| most cases is that you damage _the computer_ , the power supply
| is different, there you also have a good chance of getting
| shocked.
| aequitas wrote:
| Or just short out the capacitor terminals with a metal object
| like the screwdriver and you're fine. But still, if you don't
| do that and you get chocked it will just be a little painful
| jolt.
| formerly_proven wrote:
| I recommend against this. Most supplies have a bleed circuit,
| but if it doesn't or it doesn't work (at all or not fast
| enough), then shorting primary-side capacitors can make a
| really nice bang and also damage your "shortening implement".
| That bang can startle you and make you hit something. Been
| there done both. Not a great idea IMHO.
|
| Check for voltage - If not present / marginal, Then shorten,
| Else discharge through resistor and GoTo Check. A "capacitor
| discharge tool" automates this cycle.
| exmadscientist wrote:
| You know, you'd think that would work, wouldn't you?
|
| But dielectric soakage runs in reverse, too. So even if you
| short out the capacitor once, it can recover some voltage
| after days to months left open again. (The energy comes from
| the molecules in the dielectric relaxing, very slowly.)
|
| This isn't a problem if the designer has put in a bleeder
| resistor across the capacitor. But some designers are cheap,
| and don't want to pay the extra few cents to make their
| products non-lethal to technicians. Some are just stupid
| (yes, dumbfuck "senior engineer" coworker, I am thinking of
| _you_ here, you colossal waste of oxygen).
|
| What you want to do is short it out, with a screwdriver or
| otherwise, then keep it shorted with a gator cable or even
| resistor. Then you'll be safe even if you set the project
| aside for a week. Or three months.
| userbinator wrote:
| Dielectric absorption is a hazard for HV capacitors that
| are charged to over 1kV in normal use, since they can
| recover to dangerous voltages.
|
| Mains filter caps will be lucky to recover a few dozen
| volts, which isn't going to do much (and inside a PSU, if
| the voltage is high enough it will try to run and quickly
| discharge them anyway.)
| h2odragon wrote:
| Had a pallet of military surplus capacitors, packaged as 3
| big (soda can sized) caps on a blade frame and wrapped in
| conductive foil, plastic, then heavy paper. From the 70s
| and they were fine when i got them in 1997.
|
| I wired up an unwisely huge bank out of them for some fun
| HV experiments. They were in a shed outside and could self
| charge to useful levels in the course of a windy day. Dont
| recall the actual numbers but it could vaporize dimes
| handily.
| dendriti wrote:
| I still don't think it's a good idea for the average tinkerer
| to take apart a power supply. Almost never worth it.
| xxs wrote:
| It requires some background in electronics. Personally I
| use gloves when working on electronics and soldering. There
| is nothing sophisticated about power supplies. Pressure
| vessels is where it gets real.
| slicktux wrote:
| When I was a teenager I opened a disposable camera to explore
| its contents; the flash was charged when I touched the circuit
| and I got the SHOCK of my life. I learned about capacitors the
| stupid way.
| dghughes wrote:
| A CRT enters the room...
|
| Seriously thought electrolytic capacitors need to be respected
| but not feared.
| [deleted]
| agumonkey wrote:
| I opened quite a few, and I wonder if they have bleeder
| resistors around the tube..
|
| it's also interesting to witness a bit glass thing acting
| like a capacitor
|
| ps: for long I wanted to make a discharge rod but never
| finished it
| [deleted]
| userbinator wrote:
| _it 's also interesting to witness a bit glass thing acting
| like a capacitor_
|
| The very first capacitors were glass jars:
|
| https://en.wikipedia.org/wiki/Leyden_jar
| eurekin wrote:
| I noticed some of them include a simple light, which slowly
| gets dimmer after disconnecting the power.
|
| Is it to discharge that capacitors?
| exmadscientist wrote:
| That's discharge + indication all in one. It's a great
| solution, elegant, effective, and one of my favorites. But
| you have to find the cents for the neon (usually) bulb.
| jlgaddis wrote:
| Be careful, that's (probably) just on the DC side...
| Scoundreller wrote:
| Isn't the AC side connected to the wall prongs? I
| touch/step on those all the time after unplugging things.
| Or is there something isolated from both the DC side and
| prongs where charge could be stored up?
| garaetjjte wrote:
| Yes, there's bridge rectifier.
| parsecs wrote:
| Also a good tip to touch things with the back of your hand
| first, as the current can't force you to grip harder. This is
| more for line connected stuff though.
| LambdaComplex wrote:
| An even better tip would be to use an insulated screwdriver
| instead of your hand. Or even a capacitor discharge tool,
| since those apparently exist.
| Scoundreller wrote:
| When I had to do an air conditioning capacitor, I used a
| piece of wood with a nail. I couldn't tell if adding steel
| wool to the mix would be a good idea or not.
| toast0 wrote:
| > at the very least, use only one hand at a time to avoid
| creating a circuit through your heart.
|
| The Alanis Morissette method; I've got one hand in my pocket,
| and the other's probing a live circuit.
| coryrc wrote:
| Keep your left hand back (unless you are one of those rare
| people with your heart on the wrong side).
| geoduck14 wrote:
| This is the best thing I've read in a long time.
| agumonkey wrote:
| seconded, not to be alarmist but anything mains voltage is
| dangerous (caps are rated 400V~), shit happens fast. it can be
| a tough jolt or it can burn your skin, or pierce it or burn
| nerves or maybe shock you into worse cases
|
| i repeat danger
| LASR wrote:
| It's not even the mains voltage.
|
| There are components in there that can exceed mains voltage
| when probed the wrong way.
|
| When you start getting into the higher voltages, the body's
| resistance is much lower. It only takes a few milliamps to
| stop the heart.
| pvitz wrote:
| This happened to me as a young teenager. I tried to figure out
| which part of the power supply was broken. The case was opened,
| I measured some parts, connected it, turned it on and tested if
| it was working again and disconnected it before continuing to
| work. After the fourth time, I forgot to disconnect it before
| touching something with both hands. Fortunately, the GFCI was
| working as intended, but the cramp in my arms and a very
| strange feeling around my heart is something I will never
| forget.
|
| So, to add another advice, be sure that you have a ground fault
| circuit interrupter or residual-current device and test it
| regularly.
| Kirby64 wrote:
| Simplest solution is to discharge the power supply: i.e., flip
| the switch on the power supply and then try to turn on the
| PC/electronic/whatever. You'll discharge the vast majority of
| the energy while it attempts to power on, leaving a relatively
| safe working environment. No tools needed.
| londons_explore wrote:
| Bear in mind this is a very old power supply.
|
| A modern supply would use the same principles, but would probably
| have mostly surface mount components, a single controller IC, and
| probably separate switching supplies for each different supplied
| voltage.
| R0b0t1 wrote:
| Not really true. A lot of supplies sold use old designs, and
| some components, due to their power requirements, are only
| cheap in through-hole designs.
|
| Surface mount components exist in some cases that are very
| compact but you pay a large premium.
| zokier wrote:
| More than old, it is low-end OEM power supply. Even back in
| 2005 we already had stuff like 80 Plus ratings, active PFC,
| universal input, 600+ W output ratings etc.
| dfox wrote:
| Last time I looked at it it was not especially cost effective
| to build PC power supplies on multilayer boards. That leads to
| exactly the kind of construction as in this power supply: large
| almost completely through hole single-sided board with power
| components and one or more higher density perpendicular sub-
| boards with control logic.
| londons_explore wrote:
| 2 layer boards with smd components are now cheaper than
| single layer and through hole - simply because through hole
| requires more labour to place components and has a
| substantially higher failure rate (bad joints).
|
| Obviously some components in a power supply still need to be
| through hole for mechanical reasons, but it isn't many.
| kens wrote:
| The power supply is from 2005. By my standards that's not very
| old, but maybe because I've also been looking at power supplies
| from the 1940s :-) Specifically a 100-pound Teletype power
| supply from the Navy that used mercury-vapor thyratron tubes.
|
| http://www.righto.com/2018/09/glowing-mercury-thyratrons-ins...
| quercusa wrote:
| Two great articles, Ken!
| skynet-9000 wrote:
| Are you talking about a laptop power supply vs an ATX desktop
| power supply? Even most enthusiast ATX power supplies that I've
| seen don't use SMT for the main power board, probably because
| of the weight of the components.
|
| For example, Here's a (very packed!) modern 1600 watt (!)
| powersupply from Corsair:
| https://cdn.cplonline.com.au/media/description/POW-COR-AX160...
|
| You can definitely see that SMT is used for the distribution
| side, but you can see single-layer boards used closer to the
| A/C side as well.
| amelius wrote:
| It would be nice if the article showed some voltage or current
| plots for various places in the circuit.
| robbmorganf wrote:
| I never realized the main transformer element worked on rectified
| AC. Could someone explain why we rectify the AC power before the
| transformer? I always thought transformers worked on AC power
| anyways.
| cristoperb wrote:
| In switching mode power supplies like this, the mains AC is
| rectified and then chopped up into higher frequency pulses and
| fed to the transformer. The higher frequency allows for smaller
| transformer. It also allows for voltage regulation because the
| input pulse width (in this case via the UC3842B controller IC)
| can be altered based on the sensed output voltage.
| RL_Quine wrote:
| 50/60hz requires a large transformer core. Switching power
| supplies rectify to DC, then drive the transformer at
| potentially megahertz which increases efficiency and
| substantially reduces the size and weight of the core. For
| similar reasons aircraft use 400hz 115v supply as it makes all
| of the power conversion electronics dramatically smaller.
| jeffbee wrote:
| The standing field in a massive 60Hz transformer also
| necessitates robust inrush protection. With a transformer
| across the mains, losing the input power momentarily can
| cause a huge surge current when the input is reapplied. With
| the bridge and filter first, the inrush from being
| momentarily switched off won't be severe.
| adrianmonk wrote:
| I think they are asking this: why not use the transistor to
| chop the 50/60 Hz AC into potentially-megahertz AC? Then pass
| that chopped AC to the transformer, which could still be
| small.
|
| The motivation would be to try to eliminate the full bridge
| rectifier and the high-voltage capacitors.
|
| I'm not an EE, but I would guess the simple answer is it's
| because you can't pass a AC through a transistor, since a
| transistor not only switches but also acts like a diode.
|
| I think you could work around that (build a circuit that
| switches AC with transistors), but there must be a reason why
| you wouldn't want to. Perhaps it's because it's simpler to
| just go ahead and rectify, or perhaps there's an advantage to
| having capacitors on the high-voltage side.
| tedd4u wrote:
| Nowadays it's not an issue as much since the advent of
| digital seat-back entertainment but often, listening to
| analog passenger aircraft audio loops you can hear the
| 400Hz come through. 400Hz is noticeably sharper than G but
| between G (392 Hz) and G# (415 Hz) on the standard musical
| scale (A = 440Hz). So the 400 Hz clashes with everything.
| R0b0t1 wrote:
| You can do this but it is more expensive.
|
| There are two stages: power factor correction, and the
| forward converter. The forward converter uses a transformer
| mainly for isolation. The power factor corrector exists
| because the transformer is an inductive load. If you have
| too much of an inductive or capacitive load on a
| distribution network you affect is performance.
|
| You can make the power factor corrector, which does the
| rectification, out of active components that switch in time
| with the AC signal. This eliminates the voltage drop of the
| diodes which can be a few percentage points of efficiency
| and a fair bit of heat.
|
| If you didn't need to isolate the power supply you could
| chop mains directly but you need to manage the radiated
| noise. The current designs try to maximize safety and then
| economy and then efficiency. Coincidentally, the power
| factor correction, done correctly, also helps reduce
| radiated noise by keeping the system synchronized with the
| incoming power. (This is not precisely accurate but is an
| interesting way to think of it.)
| kens wrote:
| One problem is that when your 60 Hz AC goes to 0, your
| chopped AC will go to 0 too. You'll need to store energy
| _somewhere_ to get across the milliseconds of no power. And
| your transistor, transformer, etc will need to be larger to
| handle the peaks.
| dfox wrote:
| Circuit that tries to do this directly from AC is going to
| be more or less equivalent to active rectifier followed by
| traditional SMPS power stage (including some kind of DC bus
| with some nontrivial smoothing capacitor). In case when the
| whole thing is only supposed to work in one direction and
| input is low fixed frequency AC such construction is simply
| not worth it.
| londons_explore wrote:
| To add to this...
|
| A transformer converts electrical energy into a magnetic
| field and back into electrical energy. All the energy from a
| single 'sine wave' must be stored in the magnetic field
| inside the transformer briefly before coming out of the
| output. The transformer core is made of steel usually. For a
| given weight of steel, there is a maximum amount of magnetic
| energy it can store.
|
| That means that at low frequencies like 50/60Hz, transformers
| end up very bulky.
| whoisburbansky wrote:
| Wasn't immediately clear from GPs comment and my admittedly
| limited physics instruction, but the way you explained it
| made it seem incredibly obvious in retrospect, which is a
| rare skill, thanks!
| megous wrote:
| I built some 50Hz transformer power supplies when I was
| younger. :) They were 2x the size of the ATX power supply,
| produced like 60-100W of power, and weighed something like 2kg.
| Friends building class A audio amps were quite fond of toroidal
| transformer power supplies, too.
|
| They are easy to build, much less complex than switching power
| supplies. But as others say, less efficient and I'd guess more
| expensive, these days, unless you have some spare toroid
| transformer and high capacity low voltage capacitors laying
| around, already.
|
| Just the toroidal transformer for the 800W power supply would
| weigh like 8kg or so. :)
| phatty wrote:
| The yellow disk on the primary AC in,is a transient
| suppressor,not a capacitor.
| Scene_Cast2 wrote:
| I wonder where the losses are, and if GaN power transistors for
| switching would help with efficiency here.
|
| I like Seasonic's fanless series, but wouldn't mind getting a bit
| more power out of the same size PSU.
| gautamcgoel wrote:
| Totally agree, Seasonic's fanless line is awesome.
| londons_explore wrote:
| There are losses in every step, and power supply design is
| basically a big optimization problem to choose all the design
| parameters to minimize losses.
|
| The main components with losses:
|
| * The input capacitors are non-ideal and have some resistance.
| That resistance causes heat every time current flows in or out
| of them.
|
| * The MOSFET switch has an 'on resistance' which means it
| wastes energy when current flows through it.
|
| * The MOSFET takes a certain time to turn on or off. During
| that time it is partially on, which wastes a bunch of energy
| each switch.
|
| * The transformer has resistance in the coils.
|
| * The transformer has iron core hysteresis, which makes the
| steel of the transformer get warm as magnetic fields change in
| it.
|
| * The diode on the output side has voltage drop across it.
|
| * The capacitor on the output side has resistance.
| quercusa wrote:
| It was a real learning experience moving from ideal
| transistors to real MOSFETs in an H-bridge driving a motor.
| Gate capacitance led to lots of expensive smokefests.
| R0b0t1 wrote:
| They do help. Since HN finds it interesting I can write some on
| the most modern designs. I am currently designing a FOSS power
| supply. One of the goals is to go for high efficiency. The end
| product will use GaN and SiC elements. The different
| chemistries give different switching characteristics.
| (Interesting aside is that some topologies can run forward as
| line conditioning AND backwards as a motor inverter.)
|
| There are also supply chain and security considerations,
| though. You can buy magic PSU chips but what if you can't?
| zokier wrote:
| I'm kinda surprised there would be still significant margin
| in improving efficiency, considering that modern top tier
| PSUs are already 90-95% efficient
| R0b0t1 wrote:
| You are right, power supply improvements are asymptotic.
| It's not _just_ about total efficiency, but also about how
| the heat is generated and where you can put it. A lot of
| the newer developments don 't do a lot for total efficiency
| but produce smaller supplies by more efficiency managing
| heating.
|
| That said, most supplies for sale are based on old,
| fossilized designs created ~10 years ago, hovering at
| around 80%. If you spend more you can get the gold,
| titanium, etc. But then, even those tend to be below the
| maximum you can get, which is closer to 98% if you have
| information about your load. You can also design the system
| to have better efficiency at various loads. Typically half,
| but could be worth tracking newer CPU/mobo/GPU
| developments.
| Scene_Cast2 wrote:
| Oh neat, sounds pretty cool. Is there a hackaday project page
| or similar? Is it an ATX PSU or something else?
|
| And I'm not up to date on modern electrical design, but a
| satellite-view on industry innovations & trends would be
| interesting.
| lini wrote:
| ATX12VO[1] is a proposed major change to PSUs that hopefully will
| come in the near future. It will mean simpler (cheaper) designs
| and improved efficiency. I hope that the DIY market adopts
| ATX12VO before my next upgrade. Currently only OEMs have the
| ability build PCs with these kinds of PSUs.
|
| [1]
| https://www.intel.com/content/dam/www/public/us/en/documents...
| dhdc wrote:
| ...which puts all the DC conversion on the motherboard.
|
| Honestly, I can't tell if this is a good thing or a bad thing.
|
| On the plus side, power supplies will be much simpler to design
| and test, with potentially better efficiencies. On the other
| hand, all those additional DC-DC converters will take up quite
| a bit of space on the already crammed boards, and now you got
| more heat to manage.
| formerly_proven wrote:
| It recognizes how things are already. The 5 V and 3.3 V step-
| down converters in the PSU are pretty much only for
| Molex/SATA-connected peripherals, and those don't use 3.3 V
| anyway (99.5 % of them), since it's not guaranteed to be
| there. So the 3.3 V rail is pretty much pointless. 5 V not
| quite as much, but even in an enthusiast-level PC there will
| be probably just a handful of things actually connected to
| that - most likely SSD/HDD and maybe something like a fan
| controller.
|
| No heavy loads are connected to the 5 V / 3.3 V rails. Those
| are all supplied through the 12 V rail.
| toast0 wrote:
| > The 5 V and 3.3 V step-down converters in the PSU are
| pretty much only for Molex/SATA-connected peripherals, and
| those don't use 3.3 V anyway (99.5 % of them), since it's
| not guaranteed to be there.
|
| Yeah, not only is 3.3V not guaranteed to be there, the
| latest rev of the SATA power spec reused (at least one) of
| those pins as a signal to inhibit spin-up; used for power
| sequencing in large disk arrays, with the fun side effect
| that if you've got a PSU old enough to have 3.3v on sata
| power, and you use a hard drive new enough to support spin-
| up inhibiting, you need to either tape the pin, or cut the
| orange wire, or you can't use your disks.
| dhdc wrote:
| I am pretty sure M.2 uses 3.3V exclusively, and depending
| on the implementation, RAM sometimes gets its power from
| down regulated 3.3V as well.
|
| Though you do have a good point, nobody misses -12V and
| -5V.
| jlgaddis wrote:
| > _nobody misses -12V_
|
| Some of us (masochists) actually _like_ RS-232!
| formerly_proven wrote:
| Yes, there's actually a lot of stuff that uses 3.3 V,
| e.g. anything connected to smbus. But none of them
| connect directly to the PSU, so there is no need for the
| PSU to do it.
| whatevaa wrote:
| I remember reading about some people adding so much RGB
| stuff into their system to actually run into current (A)
| maximums on power supply 5V rail, so there might be some
| exceptions, though not many.
| agumonkey wrote:
| fair point
| NelsonMinar wrote:
| I'm still boggling at the way that power is not conducted
| electrically across the power supply but is instead air-gapped
| and pass magnetically, via transformers.
|
| Isn't that a lot of power?! A modern PC can easily draw 500W or
| more. Does that mean there's some enormous magnetic field in my
| power supply? Why doesn't that pose a problem for the things
| around it?
|
| (I cheerfully admit to being very very good at manipulating bits,
| CPU opcodes, and TCP/IP packets and knowing next to nothing about
| electrical engineering.)
| coryrc wrote:
| The magnitude of the magnetic field is small and mostly
| conducts through the ferrite for maximum efficiency; it's the
| frequency which allows so much power to be conducted.
|
| Also almost nothing in your computer is affected much by
| moderate magnetic fields. Go ahead, stick magnets all over the
| motherboard!
| kens wrote:
| The magnetic field is mostly confined to the core of the
| transformers, so your power supply isn't going to start
| attracting things like a giant magnet. This internal field is
| pretty strong, though, up to 0.3 Tesla in a ferrite core. In
| comparison, a refrigerator magnet is 5 millitesla and the
| Earth's magnetic field is 30 microtesla.
| janci wrote:
| Server power supplies are impressive. I pulled out some PSUs from
| old scrapped servers. In a smaller form factor than ATX they
| deliver more than 1kW power. You read that right. 100A at 12V
| actually.
| snypher wrote:
| 100A over how many 12V circuits? I doubt it is just a single
| circuit, or you would need a ~4AWG cable and rated connector?
| [deleted]
| ptomato wrote:
| from the PSU typically one (on hotswap supplies); e.g. on htt
| ps://cdn11.bigcommerce.com/s-qfzamxn9kz/images/stencil/or...
| the connectors on the left are just control/sense pins and
| the big beefy ones are a single 12v & ground.
| namibj wrote:
| They plug in via an edge connector straight into the mother
| board, or sometimes into a separate board that connects to
| the mother board.
| JKCalhoun wrote:
| As I recall, the Apple II was fairly advanced for having had a
| switching power supply. I understand in fact it was practically
| unheard of in consumer electronics.
|
| I know the Apple I was a kit and came with no power supply but
| every one I've ever seen the hobbyist has added a clunky linear
| power supply with a monster transformer and giant electrolytics.
|
| It's almost like the two computers stood so near but just across
| from one another on two sides of some threshhold.
| ChuckMcM wrote:
| As I recall, early switching power supplies could not pass FCC
| Part 15 compliance for home use. This was in part because
| adding the necessary shielding added cost, and in part because
| the switching supply was typically more expensive than a
| gigantic transformer and a linear voltage regulator.
| lazyweb wrote:
| > The 60-Hertz AC (alternating current) from the wall oscillates
| 60 times a second, but the power supply needs steady DC (direct
| current) that flows in one direction. The full-bridge rectifier
| [1] below converts the AC to DC.
|
| [1] https://www.youtube.com/watch?v=sI5Ftm1-jik
|
| I just knew which video is linked without clicking. ElectroBOOM
| is a treasure.
| flyinghamster wrote:
| The real treats were the bottom-of-the-barrel PSUs. I remember
| having to deal with a slew of these at work back in the early
| aughts. I remember turning on a machine one day...
| _sssFWSSSSSSSHH_ and the magic smoke came pouring out. It would
| up taking out the the motherboard and hard drive with it. I
| autopsied the dead power supply, and it was chock full of
| capacitors (some blown-out) marked "Rulycon" (note, _not_
| Rubycon).
| jhallenworld wrote:
| I had some contact with PSU designers at a name brand server
| company and learned some things:
|
| 1. Electrolytic capacitors: Only Japanese brands can be trusted
| (this sounds racist or something, but it's an actual
| requirement). They all should be de-rated for reliability (have
| 2x the voltage rating). Only exception is the main bulk filter
| capacitors, where your only reasonable choice is 450V, but these
| should be 105C. Tantalum capacitors: not allowed.
|
| 2. Main switch MOSFETs: only Infineon can be trusted. Single
| active clamp / single switch topology is a no-no due to bad
| experience. (I think the one in the article uses a diode clamp,
| so should be OK).
|
| 3. Standby supply needs its own fuse. The problem is that the
| main fuse is too big for the standby supply. If there is a
| standby supply fault, you will fill the machine room with smoke
| and your brand will be mentioned in the news when machine room is
| shut down.
|
| The current limit for any exposed 12V rail is only 20A or
| something line that (240VA UL limit), so you must not have
| exposed 12V when the server cover is open.
|
| There was basically a 100 page requirements document all along
| these lines.
| indigomm wrote:
| Japanese brands are renowned for having a very reliable
| electrolyte formula. Dell sourced some capacitors made in
| Taiwan using a stolen copy of the formulae and it cost them
| massively.
|
| https://www.theguardian.com/technology/blog/2010/jun/29/dell...
| marcodiego wrote:
| I generally think of a switching power supply as a PWM damped by
| a capacitor. Never knew exactly how oversimplified my thinking
| is.
| amelius wrote:
| The problem with this view is that a capacitor at a low
| impedance output will do nothing.
| marcodiego wrote:
| Hmmm... makes sense. Is it possible to ELI5 what should be
| put after the PWM so it can handle low impedancies?
|
| From https://www.electronics-tutorials.ws/power/switch-mode-
| power... "The Buck Switching Regulator" looks like an
| arrangement with a diode, inductor and capacitor is enough.
| Interesting.
| celim307 wrote:
| On a somewhat related note, I just found out johnnyguru, a major
| contributor to consumer psu reviews and knowledge, has shut down
| his site and forums. His tear downs were always fascinating
|
| https://web.archive.org/web/20210126113732/http://www.jonnyg...
| 45ure wrote:
| Some accrued knowledge still survives, within a community,
| which is trying to keep it alive. I wish them all the luck.
|
| http://www.johnnylucky.org/power-supplies/psu-recommendation...
|
| https://hardforum.com/forums/power-supplies.93/
| PragmaticPulp wrote:
| The computer enthusiast market is a difficult niche to cater to
| online. Most of the visitors will arrive with ad blockers
| enabled and they're going to buy products from the cheapest
| retailer directly, not through affiliate links. Also, some of
| them will be brutally combative for no particular reason.
|
| The originator of that website landed a dream job doing R&D for
| Corsair. The owner of the domain (not Johnny, as far as I can
| tell) simply decided to let it expire.
| young_unixer wrote:
| Isn't there a way to create a rectifier with just three diodes? I
| remember having come up with a way to make one when I was in high
| school, but there must have been something wrong with it. Now I
| can't remember how it was, or maybe it had 4.
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