[HN Gopher] Ask HN: Why do some electronics use 6.2 volts DC?
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Ask HN: Why do some electronics use 6.2 volts DC?
I don't know very much about electronics. I was poking around a
new device and the power supply was supplying 6.18 volts to a board
that appears to have 5v chips...the labels are rubbed off but one
has "5v" written on it. Then I looked in my box of wall warts and
saw I have a 6.2 volt adapter. So I am curious why would an EE use
6.2 rather than 5 volts? For context, the device is a tabla drum
machine. The power supply is a bit janky. It uses line level AC. I
would like to just power the board directly with a barrel plug and
that seems within my ability.
Author : brudgers
Score : 47 points
Date : 2023-04-26 17:24 UTC (2 days ago)
| hw-guy wrote:
| Just a guess...maybe the 5V is supplied from a linear regulator
| with a maximum dropout of 1.2V, so the board is specified to
| require at least 6.2V from the wall wart.
| jschveibinz wrote:
| I think you nailed it.
| RobotToaster wrote:
| That was my immediate thought too.
| Gibbon1 wrote:
| That's exactly it. Any less than the regulator won't regulate
| properly. More than that it'll dissipate too much heat.
| regularfry wrote:
| Combine this with the sibling thread about lead acid battery
| voltages (2.1V per cell, 3 cells gives 6.3V), can we then say
| that this is the reason 5V circuitry is so common? 6.3V from
| battery ancestry plus a linear regulator?
| Gibbon1 wrote:
| Yeah I think even earlier 6.3 volts was also the voltage
| used for the heating element on vacuum tubes. I think
| because very early radio's used 6V batteries for the coils.
| And a separate high voltage battery for the plates.
|
| Would not surprise me if there are roots going back to
| telegraph.
| JohnFen wrote:
| That sounds entirely plausible. Many of the hobby electronics
| projects I make require at least a 6V supply because of exactly
| this. I usually use a 9V wall wart, though, because those are
| very commonly available (so are easy to scrounge up).
| arcticbull wrote:
| For what it's worth in hobby projects it's time to throw
| linear regulators into the dustbin. There's 7805 pin-
| compatible switching modules now!
|
| Stuff like this. [1]
|
| [1] https://www.digikey.com/en/products/detail/cui-
| inc/VXO7805-5...
| stephen_g wrote:
| Depends on what you're doing. For a lot of sensors and
| things you might want the power-supply ripple rejection
| (PSRR) you get through an LDO. I'm not doing hobbyist
| things, but in our designs we have a lot of places where we
| will have a switcher that generates an intermediate voltage
| to feed a bunch of ultra-low noise, high-PSRR LDOs for
| different components (isolates them from each other too).
| This is RF though, where that is especially important.
| arcticbull wrote:
| I just meant as a replacement for your main input power
| regulator - for the 7805 way too many people still use.
|
| You are absolutely right that there is a role for LDOs in
| modern devices.
|
| There's no reason for most hobbyists to be using super
| hot, super inefficient and super constrained high-dropout
| linear regulators from 1972 when there's a pin-compatible
| all-in-one switching module for roughly the same price.
| To pull more than a couple hundred mA at the lowest
| voltage differential you need a heatsink!
| sidewndr46 wrote:
| Trying to use a switching regulator for everything
| becomes a complete nightmare when you have to debug a
| circuit. You scope something that should be a square wave
| or similar and it has the switching frequency of the
| regulator superimposed upon it everywhere.
| 83 wrote:
| 90% efficiency for $2.50ish. Pretty cool, thanks for making
| me aware of these.
| blihp wrote:
| IIRC, you can get them for ~$1 on aliexpress. They're
| handy little devices.
| kurthr wrote:
| Yep, modern LDOs can maintain 0.2-0.3V with good regulation,
| but older cheaper ones are a diode drop (~0.6V) or two.
| makomk wrote:
| Older cheaper voltage regulators are typically more like 2V
| drop and the optimum input voltage is somewhere around 7-9V
| for a 5V output. In practice a lot of devices used 9V power
| supplies because that was the lowest widely-available voltage
| that met the requirement. More modern LDO regulators would
| have plenty of headroom on plain 6V. It'd be kind of unusual
| for any electronic device to need the extra .2V in this
| particular case.
| kurthr wrote:
| I think you just described the 7805?
|
| https://www.tutorialspoint.com/what-is-voltage-
| regulator-780...
|
| It's a great old school design, but there are somewhat
| newer capless designs that are about 2 drops like the
| LM2940.
|
| There are a lot of other designs between a 0.2V current
| feedback pFET design, but not all of them have been so
| popular that their costs are close to packaging.
| tempest345 wrote:
| Around 6.3V was a standard voltage for vacuum tube heater pins
| (the part that emitted free electrons via thermal emission inside
| the tube to be available for the electrical fields to
| accelerate).
|
| My guess would be that historically 6.3V supplies made forvacumee
| tubes where commonly available when transistor based electronics
| where created so it made sense to utilize them. Works quite
| nicely for the typical 5V circuits as a "rough" input voltage to
| be feed through a LDO regulator, for example. And so it just
| stuck.
| adammunich wrote:
| 6.3V is the standard voltage of a farm tractor battery --these
| vacuum tube heaters were designed to use them.
|
| 12.6V is two farm tractor batteries (one car battery), which is
| why our computer industry uses 12V for motherboards (12 volts -
| 0.6V reverse protection diode).
|
| Early computer power supplies used voltage regulators that were
| designed for car radios, originally.
| ChrisRR wrote:
| Are you sure about that? Many computers used +-12V in the
| 80s/90s when LDOs weren't common at all
| rrobukef wrote:
| I think the cause and effect was switched. 12V was used
| because of 12.6V is two batteries, LDO's are used nowadays
| because 6V, 12V was standard.
| tiedieconderoga wrote:
| But don't 12V lead-acid batteries have a wide voltage range
| between charged (~14.5V) and discharged (~10V)? I don't think
| they would provide exactly 12.6V very often, or for very
| long.
| humanpotato wrote:
| They are not 14.5V charged. They need about 14V _to
| charge_.
|
| https://footprinthero.com/wp-content/uploads/2022/05/Lead-
| Ac...
| ddalex wrote:
| But is the SBR the width of two horses asses ?
| CoastalCoder wrote:
| Horses don't "have" asses. They're both individual
| contributors.
| [deleted]
| dghlsakjg wrote:
| That's why its pluralized
| bluGill wrote:
| Farm tractors and cars switched from 6 volt to 12 volt at
| about the same time, and for the same reasons. However the
| old 6 volt farm tractors are still around and used for
| framing, while 6 volt cars are rare collectors items (even
| though there were more of them).
| namdnay wrote:
| I think bikes are 6V, as well as stuff like quads, jet skis
| etc
| sidewndr46 wrote:
| not even close. I'm not aware of a single vehicle still
| in production with a 6 volt battery system.
|
| Many kick-start and pull-start engines do not have a
| specific voltage but may use an alternator wound with a
| number of different coils to produce different voltages.
| [deleted]
| madaxe_again wrote:
| That's because you get ~2.1v out of a single charged lead
| acid cell, and an old tractor battery contains three. Your
| car battery has six.
|
| So the real answer to "why" is because of the
| electrochemistry of lead.
|
| Kinda similar to how a lot of our world is structured around
| the dimensions of two horses side by side.
| foobarbecue wrote:
| Also the electrochemistry of sulfuric acid (the other half-
| cell)
| psychphysic wrote:
| It'd be very hitchhiker-esque if OP got the answer because
| 3x(1.69 - -0.36) ~ 6.3
| ShadowBanThis01 wrote:
| Cool info, thanks!
| eimrine wrote:
| That was my immediate thought also, but vacuum tubes I know
| commonly use 6.3V AC.
| jacquesm wrote:
| Not necessarily, they would run just fine of lead acid cells,
| 3 of which produce... 6.3V DC.
| makomk wrote:
| The filaments will run off either AC or DC because they're
| basically just heaters. AC became the norm in mains-powered
| devices after electrification took off, but a lot of the
| early radios were powered by DC from batteries - initially
| this was seperate, possibly rechargable, low voltage battery
| for the filament supply and a disposable high-voltage
| battery, with the second battery being replaced by step-up
| devices using vibrators and transformers fairly early on.
| h2odragon wrote:
| https://en.wikipedia.org/wiki/Vacuum_tube_battery
|
| Up to 120VDC early on
| schappim wrote:
| It is mostly for voltage headroom/power dissipation along w/ the
| use of 6.2V Zener diodes(hear: voltage regulation). The use of
| 6.2V also gives you some margin for noise.
| ofalkaed wrote:
| Could also be simple pragmatics or the economy of scale. If your
| business makes both 5V and 6.2V devices it could be a decent cost
| saving to make them both use 6.2V adapters, unless production
| number are low burning off that extra 1.2V in the 5V devices will
| generally be cheaper than separate power adapters for each and if
| nothing else it is one less inventory item to deal with.
| lucas_membrane wrote:
| I had a little problem with my desktop computer (Intel I7-6700
| CPU) a couple of months ago. It would start up and run OK, but
| eventually the file system would switch itself into the read-
| only state, causing it to lock up. After a few weeks of trying
| everything to fix it, I noticed that the slider switch on the
| power supply was in the 230 volt position, even though I'm
| sitting here in the USA and the thing has been plugged into the
| 115 volt mains for years. That it could just about run on half
| the voltage it required(?) makes me think that the rightmost
| digits on voltages are there for historical or marketing
| reasons only, like the old 101 mm cigarettes, the 81 mg
| aspirins, and the guitar amp that goes up to 11.
| ofalkaed wrote:
| Those digits are fairly important to EEs.
|
| Common switch mode power supplies are not picky about input
| voltages and generally have a wide range of operating
| voltages, having the switch on 230 likely just knocked 20
| volts or so off the input voltage to keep the 230 below the
| max voltage, not half it. The reason this eventually started
| causing problems is probably because your wall voltage has
| dropped and/or components in the supply aging and drifting
| from spec meant it could no longer maintain good clean output
| which triggered a safe guard in the computer.
| [deleted]
| brudgers wrote:
| Thanks. That makes sense.
|
| The rhythm machine takes AC at 120 and 220 through two separate
| figure eight female jacks. It's from India.
|
| Then there is a transformer that outputs ~6.2v from my 120v AC
| (don't know what it would be from 220). It would make sense if
| the transformer was sourced off a shelf at the cost of a
| voltage regulator which there appears to be.
| sitharus wrote:
| That's a pretty typical design for power supplies.
| Transformers output depends on the mains input. Where I am
| this is nominally 230V, but in reality ranges from 235-245V.
| So they often use a linear regulator to obtain the required
| voltage, but these need to drop from a higher voltage so they
| choose a range that would require the least dissipation.
| Majromax wrote:
| 6.2V AC? That's 9V peak-to-peak, so after rectification it
| would be 9VDC less diode drops.
| ofalkaed wrote:
| That is an odd layout*, is the schematic online somewhere?
|
| Since this is older gear, it is probably a 6.3V transformer,
| 6.3 and 12.6 volt transformers were some of the most common
| and cheapest voltages before the rise of cheap switcher
| supplies. 6.3 and 12.6 were the optimum voltages for powering
| the filaments of vacuum tubes and became standard voltages in
| transistor gear since they were cheap and available, even
| today transformers in these voltages are easy to find cheaply
| on the surplus market.
|
| *Edit: Nevermind, I read that as you had 120 and 220VAC
| transformers followed by a 6.3VAC transformer, you have one
| transformer with 120/220 primaries and a 6.3VAC secondary.
| Not odd at all.
| amelius wrote:
| Battery voltages go in multiples of about 1.5V typically. Perhaps
| that could be the reason?
| pantalaimon wrote:
| Only Alkaline batteries.
| b_t_s wrote:
| Alkaline batteries are still what runs most consumer battery
| powered gadgets. 4 alkaline batteries are nominally
| 6v(actually 5-6.6 depending on charge), so 6.2v seems perfect
| if you want to run a 4x battery device on a more permanent
| power source.
| jacquesm wrote:
| And carbon-zinc batteries too. And at 6V all of these
| architectures have a nice common multiple (3x2 or 4x1.5).
| lmpdev wrote:
| Can zinc carbon batteries just go and die?
|
| I struggle to see how they're legal
|
| They're one step away from landfill out of the
| manufacturer's doors
| jacquesm wrote:
| Yes, they're pretty bad. But they're cheap and that's why
| they still exist. The number of toys that I've repaired
| on account of those leaking - unprintable - s is larger
| than I care to remember. And yet people keep buying them.
| I'm pretty sure I've seen the _same_ toys more than once.
| ofalkaed wrote:
| It could also be that some of the circuit needs a higher voltage,
| just because some parts are 5V does not mean they all are.
| guerrilla wrote:
| Definitely sounds like a linear regulator is in use.
| [deleted]
| lmpdev wrote:
| Possibly a linear regulator (does the device get warmer than
| you'd expect?)
|
| Although the LM7805 would need ~7V minimum
|
| RE those chips: almost all general purpose components have a
| usable voltage _range_. From LEDs to MCUs, most components can
| tolerate a few hundred millivolts from its ideal V_{f}, some even
| dozens of volts - especially solid state stuff like CMOS ICs
|
| The only time I really recommend not f*cking with aftermarket
| PSUs is if it's primarily charging or powering: - lithium
| batteries - super or ultra capacitors
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(page generated 2023-04-28 23:02 UTC)