[HN Gopher] Things you can do with diodes
___________________________________________________________________
Things you can do with diodes
Author : zdw
Score : 363 points
Date : 2025-11-03 23:49 UTC (23 hours ago)
(HTM) web link (lcamtuf.substack.com)
(TXT) w3m dump (lcamtuf.substack.com)
| jagged-chisel wrote:
| > ... There is a positive charge on the n-side and a negative
| charge on the p-side.
|
| How completely unintuitive.
| Shellban wrote:
| You can blame Benjamin Franklin for that. By the time we
| figured out the mistake, the standards were set in stone.
| dietrichepp wrote:
| It would be like this either way.
|
| The N side has negative charge carriers. It has a positive
| charge in the depletion region because the charge carriers
| are missing. Likewise, the P side has positive charge
| carriers, and when they're missing, you get a negative
| charge.
|
| This is true whether we live in the current universe or live
| in an alternate universe where we say that electrons have
| positive charge. The depletion region is where the charge
| carriers are _missing_ (depleted), so you get the opposite
| charge of whatever the charge carriers are.
| dietrichepp wrote:
| Conspicuously absent are some of the analog circuit applications.
| Here are three of my favorites:
|
| 1. Frequency mixer, used for heterodyning, important in radio, so
| I hear. https://en.wikipedia.org/wiki/Frequency_mixer
|
| 2. Log converter, where the output voltage is proportional to the
| logarithm of the input voltage.
| https://electronics.stackexchange.com/questions/374440/log-c...
|
| 3. Diode ring, which provides variable gain, used in analog
| compressors like the Neve 33609 (I have a clone of the 33609, and
| I'm very fond of it)
|
| Think about this: if you have a nonlinear device like a diode,
| then the dynamic resistance changes depending on the operating
| point. If you modulate the operating point, you're modulating the
| dynamic resistance.
| hshdhdhehd wrote:
| From my hobbying decades ago there is also the boring old
| rectifier to convert AC to a wavy DC.
| kennywinker wrote:
| Those are covered in the article
| nomel wrote:
| 4. Varactors! https://en.wikipedia.org/wiki/Varicap
|
| Reverse biasing a diode at different levels changes the
| junction capacitance. Also used in radio, for things like
| variable filters.
|
| edit: oh, it's topped pinned comment!
| bob1029 wrote:
| Zener diodes can be used as the basis for a quantum random
| number generator.
|
| https://opg.optica.org/optcon/fulltext.cfm?uri=optcon-1-7-15...
| phkahler wrote:
| These are also good noise sources and were use in several
| early video arcade games for producing explosion and
| spaceship thrust sounds.
|
| https://en.wikipedia.org/wiki/Noise_generator
| beckler wrote:
| Kinda interesting to hear about. I have a 500 chassis I'm
| slowly working on filling. I'm between the RND 535 or 543, and
| had never heard of a diode bridge comp before looking at the
| 535.
|
| What kind of 33609 clone do you have?
| dietrichepp wrote:
| I have the Heritage HA-609A. I considered going 500-series.
| Maybe some day in the future. For now, I have two preamps and
| the HA-609A in a 4U rack, and most of my other gear is in
| storage. Keeping things light.
| RossBencina wrote:
| 4. Voltage controlled filter, (diode ladder VCF), as used in
| the Roland TB303
| ErroneousBosh wrote:
| Diode ladder, but also in various Sallen-Key designs like the
| Steiner-Parker Synthacon which we all now know from the
| Arturia Minibrute (Yves Usson probably made more of these
| filters than Nyle Steiner ever did!) and as I've mentioned
| elsewhere the Korg MS50. I think the Yamaha GX1 filters used
| a diode bridge too, probably using discrete transistors
| similar to the Korg 700S filter.
| cozzyd wrote:
| And a square law detector!
| gblargg wrote:
| Temperature sensor.
| liffiton wrote:
| I did this once with a diode when I was a baby electrical
| engineer in college. But of course you need some kind of
| measurement circuit. So somehow(???) I figured out I could
| wire a diode into one axis of my analog Gravis joystick--
| hooked up to my soundcard--and get a fairly accurate and
| stable measurement of temperature by poking the monostable
| multivibrator (pretty sure that's what it was called) in the
| soundcard that would trigger the time it took to drain a set
| amount of charge through the joystick's x-axis/now-diode.
|
| Novices who don't have a clue nor know any better come up
| with the weirdest solutions. I have no clue whatsoever now
| what inspired me to even try something like that.
| ErroneousBosh wrote:
| > I have no clue whatsoever now what inspired me to even
| try something like that.
|
| A combination of "what's the simplest thing that could
| possibly work?" and "well they didn't say you couldn't..."
| HeyLaughingBoy wrote:
| And you managed to reinvent the single-slope ADC :-)
|
| https://www.cedarlakeinstruments.com/archives/841
|
| https://www.monolithicpower.com/en/learning/mpscholar/analo
| g...
| summa_tech wrote:
| You could also make a high speed signal sampler.
|
| https://w140.com/tekwiki/wiki/Sampler
| temporallobe wrote:
| Clipping diodes are common in distortion effects as well,
| especially guitar distortion pedals. Examples include silicon,
| germanium, LEDs, etc.
| normel6 wrote:
| PIN diode, a diode used as an AC on/off switch by passing
| current through it, very useful in RF circuits above 1GHz
| analog31 wrote:
| I'm always amazed at the circuit hacks that look utterly
| disgusting until you realize that they're the most practical
| solution at high frequencies.
| joconne wrote:
| Diodes are also used as a radiation detector in radiotherapy:
| https://oncologymedicalphysics.com/diode-detectors/
| 4gotunameagain wrote:
| And particle accelerators ! They mostly detect gamma
| radiation, and they are used in conjunction with other
| detectors (ram chips, mosfets)
| f1shy wrote:
| With some capacitors you can build a voltage multiplicator
|
| https://en.wikipedia.org/wiki/Voltage_multiplier
| timonoko wrote:
| Stereo decoder. You feed L+R and L-R to the corners of _Full
| Bridge Rectifier_ and out comes Left and Right.
| goodpoint wrote:
| I heard his voice while reading this.
| exDM69 wrote:
| Two more from the world of analog music/guitar electronics:
|
| 1) Ring modulator:
| https://en.wikipedia.org/wiki/Ring_modulation
|
| A device used to multiply two analog signals in time domain.
| Best known for the sound of the Daleks in the original 1960s
| Doctor Who series. Has some applications outside of music and
| sound effects. If you can find those old fashioned audio
| transformers, this effect does not require a power source.
|
| 2) Diode clipper:
| https://en.wikipedia.org/wiki/Clipper_(electronics)
|
| Two diodes in parallel with opposite polarities. Clips the
| incoming AC signal to a +/- diode threshold voltage. Put a high
| voltage gain amplifier stage in front of it and you get the
| classic electric guitar distortion tone you know and love.
| Allegedly works best with germanium-unobtainium diodes. In
| their absence, using two different kinds of diodes can also
| have pleasant tonal qualities.
| ErroneousBosh wrote:
| > 2) Diode clipper:
| https://en.wikipedia.org/wiki/Clipper_(electronics)
|
| I don't even know how many Boss DS-1 clones I've made, but
| the first one was probably when I was in high school about 35
| years ago.
| actsasbuffoon wrote:
| So many distortion pedals use an op amp to run a signal into
| antiparallel diodes to create distortion. I've spent a few
| weeks trying to emulate it, and it's a lot of fun.
|
| Different flavors of diode make significant changes to the
| way it sounds. Even things like LEDs can be used (they are
| Light Emitting Diodes, after all).
|
| Andy Simper of Cytomic is some kind of mad genius at this
| stuff. He's created a painstakingly accurate emulation of the
| Ibanez Tube Screamer that allows you to change the values of
| basically every component in the circuit diagram. It's jaw
| dropping: https://cytomic.com/product/scream/
|
| He's also shared a ton of incredible information about how he
| emulates circuits. The math can get really intense. If anyone
| is looking for a fun project, I strongly suggest
| experimenting with circuit modeling. It's a great workout for
| the brain.
| Archit3ch wrote:
| As someone also doing audio circuit modeling, Andy is so
| far ahead of everyone in this game. Have you seen his
| latest? https://www.kvraudio.com/forum/viewtopic.php?p=9149
| 872#p9149...
| squarefoot wrote:
| > If you can find those old fashioned audio transformers,
| this effect does not require a power source.
|
| Audio transformers are available both on Aliexpress and Ebay,
| although I would probably trust more a Triad TY-250P which is
| about EUR5 each at Mouser.
| adrian_b wrote:
| For log converters you should not use diodes, because their
| parasitic currents mask the current component that has an
| exponential dependence from the voltage.
|
| For log converters, bipolar transistors are used, because their
| collector current depends only on the ideal diode current of
| the base-emitter diode, not also on its parasitic currents, so
| the base-emitter voltage has a logarithmic dependence on the
| collector current, for a relatively wide range of currents.
| ErroneousBosh wrote:
| > 3. Diode ring, which provides variable gain, used in analog
| compressors like the Neve 33609 (I have a clone of the 33609,
| and I'm very fond of it)
|
| I just had a quick look at the service manual, but isn't that
| more of a diode bridge than diode ring? A Ring Modulator has
| the diodes connected nose-to-tail in a ring, but the gain cell
| in the 33609 looks more like a rectifier :-)
|
| You can see the same circuit in the VCF and (incorrectly drawn)
| in the VCA of the Korg MS50 synthesizer. In the former it acts
| as the "variable resistor" in a fairly straightforward Sallen-
| Key lowpass filter (there are two feedback capacitors, one to
| either side of the bridge, to attempt to prevent the input
| voltage also tuning the filter). On the VCA the diodes are
| drawn wrong but the pin numbers are correct.
| stevefolta wrote:
| In synthesizers, diodes are used in oscillators to shape
| triangle waves into sine waves.
| namibj wrote:
| Step recovery diode!
|
| Abuse minority carrier lifetime to very suddenly turn from
| resistive to capacitive just after switching from forward
| current to reverse bias; use the fact that the current wants to
| keep flowing to force it to concentrate into another step
| recovery diode that's about to cut out, in turn making the cut
| off spike even sharper, and on.
|
| Surprisingly capable for e.g. blasting a FET gate off while
| tanking the Miller effect gate current needs through sheer
| power of SRD-based-pulse-shaping. Because for e.g. GaN and SiC
| if you have to choose between ZVS and ZCS, you can take ZVS and
| just furnish a gate pulse that _makes_ the channel remain off
| as the current drops and the voltage soars. At least if you
| pull some tricks and make the current commutation loop
| sufficiently low inductance to keep your transistors from
| blowing out in self-inflicted overvoltage due to a current that
| needed to pass too high an inductance in too short a time.
| (Total drain charge is sadly fundamental to the channel's
| existence, and non-ZVS turn-on is unavoidably lossy. A majority
| carrier device is theoretically capable of just switching off
| though if you can arrange the structure for extremely low
| inductance.)
| hshdhdhehd wrote:
| Current/voltage chart looks a lot like a RELU.
| CamperBob2 wrote:
| That's exactly why it's called a 'rectified' linear unit! It's
| a half-wave rectifier. The ReLU function is just what you'd see
| if you put an (ideal) diode on a curve tracer.
| CamperBob2 wrote:
| (Although to be more accurate, it would be what you'd see on
| an I-V curve tracer if you measured an ideal diode in series
| with a 1-ohm resistor. The diode by itself would just go
| vertical at the Y axis, and the ML people would mutter into
| their beards about exploding gradients.)
| hshdhdhehd wrote:
| And that diode would be an exploding grenadiant?
| CamperBob2 wrote:
| Yes, because the slope of current versus voltage goes
| infinite as soon as the voltage goes positive. The math
| would explode, and so would the diode, given enough
| current.
| Cymen wrote:
| Also missing solar heating from diodes:
|
| > This topic seems to be broadly misunderstood. It is 100%
| verified fact by both myself and others (including university
| researchers) that diode strings can produce more heat (or watt-
| hours, BTU) from a given solar panel than a bare resistance
| element.
|
| https://www.youtube.com/watch?v=42XIbHA9Dv0
| Retr0id wrote:
| Intriguing, but wouldn't it be even more efficient to just
| paint something black and let the sun heat it directly?
| Scoundreller wrote:
| depends how hot you want to get something
| cwillu wrote:
| At the cost of very efficiently radiating that heat back out
| into space at night.
|
| Making electricity and then using that electricity to heat
| something elsewhere lets you insulate, effectively allowing
| you to create a box that heat energy can only pass one way.
| jaggederest wrote:
| We have a one-way diode technology for heat, it's called
| "glass", and it'll bump your efficiency by about 25% versus
| uncovered flat plates on a still day. More in windy
| conditions etc, lots of hand waving assumptions about
| spherical cows in a vacuum etc.
| b00ty4breakfast wrote:
| You'd need some kind of storage for the heat, something with
| a large thermal mass that doesn't readily give up it's heat
| to the surroundings. Sand or water or even big rocks or a
| thick slab of concrete.
| petermcneeley wrote:
| where is this 'extra' heating coming from?
| labcomputer wrote:
| I suspect (didn't watch) it's just that a diode makes a crude
| MPPT tracker (since a PV array is just a bunch diodes
| arranged to collect photons at the P-N junctions). The
| benchmark is probably "non-variable resistor".
| Scoundreller wrote:
| my thought was that a diode removes all the current from
| its voltage drop (aka: why your LED will burn out if it
| gets uncontrolled current). A resistor will never remove
| all the current going through it.
|
| Maybe we're saying the same thing in different ways.
| Tuna-Fish wrote:
| You suspect correctly.
|
| For people who don't know much about solar panels mystified
| about this:
|
| Solar panels are not ideal voltage sources, their internal
| impendance varies depending on temperature and the amount
| of light falling on the panels. Because the point of
| maximum power in the circuit is achieved when the internal
| and external impendances are matched, a simple resistive
| circuit is inefficient and results in the panel converting
| less light into electricity. If you had a variable
| resistor, you could adjust it over the day to match the
| panel, but it is of course easier to use a semiconductor
| device that does this for you. Any halfway decent battery
| charger setup or PV inverter has one, but if you are
| building your own heating system, just stringing together a
| bunch of diodes might sound stupid, but totally works.
| nandomrumber wrote:
| From the misleading sound-bites themselves, they're know to
| increase conversation metrics.
| labcomputer wrote:
| TL;DW: Isn't that just because the diode matches the PV array's
| max power point, assuming they both use the same technology
| (e.g., silicon)?
|
| It seems like that depends on the diode string and PV array
| remaining at approximately the same temperature as heat is
| dumped into the diode.
| ErroneousBosh wrote:
| > It is 100% verified fact by both myself and others (including
| university researchers) that diode strings can produce more
| heat (or watt-hours, BTU) from a given solar panel than a bare
| resistance element.
|
| In some of my early experiments with little radio transmitters
| some 30-odd years ago I managed to burn my fingers to an
| astonishing degree with little plastic transistors like ZTX300s
| and BC548s.
|
| I remember my late father also commenting around that time "How
| come a 2N3866 which is rated for a couple of watts can get so
| hot it melts all its legs off when it's running off a half-flat
| PP3 battery?", astonished as yet another 2N3866-based amp got a
| bit lively and melted its legs off despite only running off a
| half-flat PP3 battery.
|
| So yes I can believe a string of diodes would be a more
| effective heater than a resistor.
| wormius wrote:
| I know we're on hacker news, but let's just say I misread the
| title.
| tt_dev wrote:
| Was looking for this comment
| devsda wrote:
| And keeping up with the spirit of HN, we would have hopefully
| learnt something new either way.
| jug wrote:
| I went up 4:30 am today for a flight to Gothenburg, pretty
| tired and slow... and you and me both.
| uticus wrote:
| > The reason I put "gate" in scare quotes in the illustration is
| that the circuits are not readily composable to implement more
| complex digital logic...
|
| Any good suggestions on resources talking about building complex
| digital logic out of something more suitable?
| JKCalhoun wrote:
| They might be referring to RTL (resistor-transistor logic). A
| transistor in the circuit can maintain the same output current
| that was input. (A transistor in fact a diode and a half.) RTL
| was superseded by TTL (transistor-transistor logic) but, hey,
| the Apollo computers that put astronauts on the Moon used RTL
| logic.
|
| You could start with the late Don Lancster's book [1].
|
| I have a little "breadboard helper" that I am wrapping up (that
| includes a project manual) for creating RTL circuits and others
| [2]. (I hope to sell a few.)
|
| RTL book [1]: https://archive.org/details/RTL_Resistor-
| Transistor_Logic_Co...
|
| Prototyping [2]:
| https://cdn.bsky.app/img/feed_fullsize/plain/did:plc:oxjqlam...
| cwillu wrote:
| https://en.wikipedia.org/wiki/Logic_family has a list of common
| families; of particular note is CMOS, which is essentially what
| modern computing is based on.
| _whiteCaps_ wrote:
| Bebop To The Boolean Boogie might be useful for you - it's kind
| of a kids book but the concepts are all well done.
| Tuna-Fish wrote:
| While diodes alone are not suitable for complex logic, they
| were instrumental on making computers cheaper in the late
| vacuum tube era. Vacuum tubes have fairly low reliability and
| short usable life so having too many of them in your computer
| is really bad for the cost and reliability of your system.
| Early transistors were not much better. They would _get_ better
| over time, but cheap, reliable mass produced diodes were
| available long before transistors got there.
|
| And while diodes alone cannot do it, a system with a few vacuum
| tubes to provide the gain and driving a whole lot of diodes
| made a lot of computers possible at price points that vacuum
| tubes alone could only dream of. An example is the hacker
| folklore sweetheart LGP-30, of _The Story of Mel_ fame. 113
| vacuum tubes driving 1500 diodes made for a computer that was
| the size of a fridge, weighed 800 pounds, drew 1.5kW and cost
| $50k (~500k in modern money), which made it pretty much a
| personal computer for the late 50 's.
| brucehoult wrote:
| He mentions diode logic and points out the drawback of the
| limited output current, but doesn't mention the obvious solution
| of a transistor in voltage-follower configuration.
|
| I always thought RTL was pretty nifty, and it was used in a lot
| of early computers. I think it's a lot less fussy of component
| values than the earlier RTL.
| djmips wrote:
| And here's another that's always fascinated me -> Diode Ladder
| Filter.
|
| https://www.youtube.com/watch?v=jvNNgUl3al0
| iainctduncan wrote:
| Diode ladder filters are a mainstay of old analogue synths...
| and sound awesome.
| youngtaff wrote:
| They certainly do... I've few in my Eurorack synth
| skopje wrote:
| forgot adc converter! series diodes tapped at each connection.
| kazinator wrote:
| Another one: Baker clamp to speed up a transistor.
|
| https://en.wikipedia.org/wiki/Baker_clamp
|
| Flyback diode:
|
| https://en.wikipedia.org/wiki/Flyback_diode
|
| A diode can switch off an AC source when a battery is present:
| see second circuit in accepted answer, introduced by,
| "Alternatively, you can probably get away with just using some
| schottky diodes:"
|
| https://electronics.stackexchange.com/questions/71753/whats-...
|
| Also, diodes can be used to provide a controlled discharge path
| for capacitors when a device is turned off.
|
| The circuit in this EE StackExchange question shows it:
|
| https://electronics.stackexchange.com/questions/471285/capac...
|
| It has one RC constant when charging and a different RC constant
| when discharging through the diode.
|
| Why would you want to charge a capacitor slowly when power is
| applied to the device, but discharge it fast when power is cut?
| There are various applications for that.
|
| For instance, circuits that control some timed behavior, like
| holding a CPU chip in a reset state at start up while power
| stabilizes, and then releasing it. You want that circuit to reset
| itself quickly if power is lost.
|
| Analog circuits have things like that in them: for instance
| circuits that mute an audio amplifier on power up for a bunch of
| milliseconds until a capacitor charges. If the power is cycled,
| you want that timer to reset itself.
|
| Another application: Log amp:
| https://en.wikipedia.org/wiki/Log_amplifier
|
| This exploits the diode's characteristic V-I exponential curve in
| amplifier feedback to produce output proportional to the
| logarithm of the input.
| sehugg wrote:
| You can put a small ROM on your board with diodes, for example to
| store bitmaps, and for style points you can even arrange the
| diodes in the shape of your bitmaps:
| https://technologizer.com/2011/12/11/computer-space-and-the-...
| zh3 wrote:
| In some early computers, the bootstrap was actually a matrix of
| diodes where you'd remove a diode to get a one and leave it in
| for a zero. I had a bunch of these boards sometime in the mid
| 1970's and found you could program a fully populated board with
| a 9V battery - basically connect it across a diode in a bit
| position where you wanted a '1', there would be a small but
| pretty flash from inside the glass case as a zero turned into a
| one.
|
| When things like the 74S188 were available, we had so much fun
| squeezing bootstrap code for PDP11's into 2 of them; 32 words
| by 16 bits was more than enough (later I got code that would
| boot five different devices into 256 words).
| petermcneeley wrote:
| Btw you can try these out online with a circuit simulator
|
| https://www.falstad.com/circuit/circuitjs.html
| atan2 wrote:
| Nice timing. I just saw pikuma's email with his new course on
| digital electronics and saw this here.
| iainctduncan wrote:
| I'ma just leave this bad boy here....
| https://www.youtube.com/watch?v=xNF891FVC6M
|
| AJH Synth Sonic V Diode Ladder Filter. (IMHO AJH make the best
| eurorack filters out there..)
| mitthrowaway2 wrote:
| You can extend the voltage doubler idea to even higher voltages
| with the voltage multiplier:
|
| https://en.wikipedia.org/wiki/Voltage_multiplier
| WorldPeas wrote:
| or.. detecting a nuclear event?
| https://www.alldatasheet.com/datasheet-pdf/view/124266/MAXWE...
| compumike wrote:
| You can simulate a bunch of these (and edit too) in your browser
| in CircuitLab:
|
| Diode half-wave rectifier
| https://www.circuitlab.com/editor/4da864/
|
| Diode full-wave (bridge) rectifier
| https://www.circuitlab.com/editor/f6ex5x/
|
| Diode turn-off time https://www.circuitlab.com/editor/fwr26m/
|
| LED with resistor biasing
| https://www.circuitlab.com/editor/z79rqm/
|
| Zener diode voltage reference
| https://www.circuitlab.com/editor/7f3ndq/
|
| Charge Pump Voltage Doubler
| https://www.circuitlab.com/editor/24t6h3ypc4e5/
|
| Diode Cascade Voltage Multiplier
| https://www.circuitlab.com/editor/mh9d8k/
|
| (note: I wrote the simulation engine)
| dr_kiszonka wrote:
| Looks great! Would you have a recommendation for intro
| materials to help me learn the _basics_ of electronics using
| CircuitLab? I have a working understanding of signal processing
| but building an actual circuit without electrocuting myself,
| not setting my Raspberry Pi on fire, or selecting the right set
| of components for the simplest DIY project based on spec sheets
| are a mystery to me.
| compumike wrote:
| Not sure if it's a fit for what you're looking for, but maybe
| https://ultimateelectronicsbook.com/ (maybe more theoretical
| than practical).
|
| I've heard good things about "Practical Electronics for
| Inventors" but haven't gone through it myself.
| MisterTea wrote:
| > Diode Cascade Voltage Multiplier
|
| A favorite of mine and one of the most common ways to generate
| a pretty high voltage DC. The full wave version pairs well with
| a center tapped secondary of a resonant transformer.
| blankx32 wrote:
| Lectenna / Rectenna https://en.wikipedia.org/wiki/Rectenna
| mattclarkdotnet wrote:
| This is excellent but in typical low voltage scenarios (5V or
| lower) the 600mV diode voltage drop becomes very significant.
| Simple diode half wave rectification works fine at 100V, but at
| 3.3V it breaks down.
| xxs wrote:
| at that point (and in general) you'd like to use Schottky ones.
| MOSFETs are an option for low extra efficiency.
| tiniuclx wrote:
| You can also build a rectifier with no voltage drop using an
| op-amp with some diodes in the feedback loop. But that might be
| considered cheating :)
| jotux wrote:
| For low voltage diodes you can use mosfets to get ultra low
| voltage drop, or just buy dedicated "ideal diode" components
| that are specifically for that:
| https://www.analog.com/media/en/technical-documentation/data...
| TrackerFF wrote:
| If you're into audio, they can easily be used for distortion. You
| "clip" the top of the audio wave. Usually in a asymmetrical way,
| to get more pleasant sounding distortion.
| tuggi wrote:
| Also the octaver...
|
| https://www.geocities.ws/diygescorp/diodeoctaveup.gif
| eimrine wrote:
| I have used some regular diodes today as a way to lower the input
| voltage and this case is not covered. A diode might be more
| effective than a buck converter because all I wanted was to have
| a 0.7V lower voltage and the converter can not work in this
| condition. Zener diode can but it dissipates too much heat for
| high-current application.
| wkjagt wrote:
| Interesting coincidence. I should receive a bunch of diodes from
| digikey today to fix the bridge rectifier on the control board of
| our pool heater.
| jamesnorden wrote:
| You can also use a bunch in series as a cheap voltage dropper (eg
| to make a PC fan run slower/quieter).
| speff wrote:
| Is (like the article said) this information really not taught in
| electronics curriculum anymore? It's been a while since I was in
| school, but this was all covered in my undergrad EE 2XX/3XX
| classes. Do modern designs use fewer diodes and more ICs in their
| place?
| ToddWBurgess wrote:
| This article reads like study notes for the Canadian Advanced ham
| license exam. It's a great crash course on diodes.
| howmayiannoyyou wrote:
| I misread the title at first and forwarded this to my wife.
| ee99ee wrote:
| I'll be honest. I misread the title as "Things you can do with
| dildos"
| AbstractH24 wrote:
| And good for you for saying outloud what many other people also
| experienced
| kps wrote:
| Wait 'til you hear about vibe coding.
| uvaursi wrote:
| > The diode might be the most neglected component in the
| electronics curriculum today.
|
| Nonsense like this is why I don't read lcamtuf. His "electronics
| 100" falls short of any standard-issue books - today and in the
| past. And you can open any of them up and very often the very
| first thing they discuss is the Diode, not only because it's an
| "easy" case to begin understanding semiconductor materials (as
| opposed to tube diodes), but because it forms the basis of
| understanding more complicated semiconductor devices and why they
| work the way they work.
|
| I've been wholly unimpressed by lcamtuf's output on this subject
| because he's trying to teach but doesn't know how. He's trying to
| come across as smart but his covering of the subject matter is
| dwarfed by someone like Forrest Mims, which is amusing to think
| about.
|
| Pick up a book by someone like Melvino or Floyd. They cover
| analog, digital, computer systems, all sorts of shit. Even the
| old NEETS books along with technician manuals are a godsend.
| NEETS approach is particularly good because it moves between
| phenomena and application in a broad spectrum, which is what
| helps for concepts to stick.
| kens wrote:
| The description of forward current and the graph are completely
| wrong. The graph shows approximately linear current above 600 mV,
| and the text says "When the threshold is cleared, the diode
| admits current that's roughly proportional to the "excess"
| applied voltage, an ohmic behavior that's a consequence of the
| resistance of the material itself".
|
| The current through a diode is exponential with voltage, not
| "proportional". The graph shows 1.6V applied to a diode yielding
| 250 mA. In reality, this isn't possible since you'd get a huge
| current and destroy the diode.
|
| See the Shockley diode equation:
| https://en.wikipedia.org/wiki/Shockley_diode_equation
|
| I'm surprised that nobody has mentioned that the article is
| messed up, so am I missing something here?
| manwe150 wrote:
| The Wikipedia equation there mentions the formula ignores the
| contribution of the internal resistance, which would make it
| proportional. It seems the article assumes that resistance is a
| significant contribution (possibly even just from their voltage
| source) while you assume it is not, for any given particular
| diode being evaluated or measured, either could be right
| bombela wrote:
| Wikipedia says:
|
| > Internal resistance causes "leveling off" of a real diode's
| I-V curve at high forward bias. The Shockley equation doesn't
| model this, but adding a resistance in series will.
|
| For small diodes and all LEDs as far as I know, it will level
| alright. Leaving behind a cute little smoldering crater where
| the now vaporized diode used to be.
|
| https://www.onsemi.com/download/data-sheet/pdf/1n4001-d.pdf
|
| Take this very generic diode here. When mounted as instructed
| for the highest heat dissipation, it should gain 50degC per
| Watt. The flattening of the Current-Voltage curves starts at
| around 1A. As the diode heats up, the resistance lowers.
| Extending the limits.
|
| Maximum before damage is 150degC. Minus 25degC ambient leaves
| us 125degC. Divided by 50degC/W gives us 2.5W. Around 2.8A-3A
| at 0.8V-0.9V forward voltage.
|
| But the curve is barely proportional at 5A. You might also
| notice that the datasheet doesn't provide numbers beyond that
| point. Presumably because the diode left the room then.
| SAI_Peregrinus wrote:
| In practical diodes it's much more likely to be a minimal
| contribution.
| SAI_Peregrinus wrote:
| > The diode is given neither the mathematical rigor of linear
| circuits nor the red-carpet treatment of the transistor
|
| Sedra/Smith dedicates Part I chapter 4 (pages 174-229 in the 7th
| edition, not counting the exercises) to diodes. That's longer
| than chapter 5 (MOSFETs) or chapter 6 (BJTs), and a substantial
| portion of chapter 3 is devoted to pn junctions. "The Art of
| Electronics" by Horowitz & Hill dedicates less space to diodes,
| but it's also much less mathematically rigorous. And they have
| you building radios & diode mixers before they introduce any sort
| of transistor. So I'm not sure I agree with this line since
| neither of the two most popular university electronics textbooks
| really fits that characterization. It's definitely true of many
| online electronics "tutorials" though.
| uvaursi wrote:
| Thank you. I was on the fence posting my comment earlier but
| I'm glad I'm not the only one who is tired of blog posters
| leading a subject with a blatantly false statement.
| shevy-java wrote:
| Back in the oldschool days in the 1990s, I remember our school
| had soldered diodes, that is, we pupils had to do so manually.
| That was quite fun. Unfortunately I haven't quite had a need or
| use case to do so again; I tried to get into arduino, but I found
| it too much needing self-learning. With that I mean I'd have to
| understand a lot in order to do something useful. I have no
| problem with learning something new, but my time is super-limited
| these days and I need to prioritize hard, so I kind of gave up.
| Perhaps I try for Raspberry Pi but I am afraid it will also
| require a lot of time investment before it becomes "useful"
| (aside from learning something new, which is always useful, but
| other things also need to be learned, so time is of limited value
| here).
| hinkley wrote:
| I had a friend in high school who brought in the Tesla coil he
| made with among other things a PSU from an old computer.
|
| I pestered that kid so hard about DC-DC voltage regulators and he
| did not know enough electronics to design one from first
| principles. I think ladder circuits was as far as he got. But I
| wanted step-down not step-up transformers.
|
| 15 years later when the first gen of really good LED flashlights
| with built-in voltage regulators popped up I owned at least one
| at all times.
| lightedman wrote:
| Not present and ultimately-cursed - using LEDs not only as bridge
| rectifier but also as the voltage drop for power conditioning
| before going into a processing IC.
|
| I'm not called the LED Punisher without reason!
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