Things you can do with diodes

> ... There is a positive charge on the n-side and a negative charge on the p-side.

How completely unintuitive.

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.

From my hobbying decades ago there is also the boring old rectifier to convert AC to a wavy DC.

Current/voltage chart looks a lot like a RELU.

You can blame Benjamin Franklin for that. By the time we figured out the mistake, the standards were set in stone.

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!

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

I know we're on hacker news, but let's just say I misread the title.

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.

Intriguing, but wouldn't it be even more efficient to just paint something black and let the sun heat it directly?

depends how hot you want to get something

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...

> 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?

Was looking for this comment

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?

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...

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.

4. Voltage controlled filter, (diode ladder VCF), as used in the Roland TB303

And here's another that's always fascinated me -> Diode Ladder Filter.

https://www.youtube.com/watch?v=jvNNgUl3al0

forgot adc converter! series diodes tapped at each connection.

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.

And a square law detector!

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.

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.

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-...

Btw you can try these out online with a circuit simulator

https://www.falstad.com/circuit/circuitjs.html

Nice timing. I just saw pikuma's email with his new course on digital electronics and saw this here.

where is this 'extra' heating coming from?

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.

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".

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..)

Temperature sensor.

You could also make a high speed signal sampler.

https://w140.com/tekwiki/wiki/Sampler

You can extend the voltage doubler idea to even higher voltages with the voltage multiplier:

https://en.wikipedia.org/wiki/Voltage_multiplier

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.

Bebop To The Boolean Boogie might be useful for you - it's kind of a kids book but the concepts are all well done.

From the misleading sound-bites themselves, they’re know to increase conversation metrics.

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.

or.. detecting a nuclear event? https://www.alldatasheet.com/datasheet-pdf/view/124266/MAXWE...

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.

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.

Diode ladder filters are a mainstay of old analogue synths... and sound awesome.

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.

And keeping up with the spirit of HN, we would have hopefully learnt something new either way.

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)

Clipping diodes are common in distortion effects as well, especially guitar distortion pedals. Examples include silicon, germanium, LEDs, etc.

Lectenna / Rectenna https://en.wikipedia.org/wiki/Rectenna

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.

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.

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.

at that point (and in general) you'd like to use Schottky ones. MOSFETs are an option for low extra efficiency.

Those are covered in the article

PIN diode, a diode used as an AC on/off switch by passing current through it, very useful in RF circuits above 1GHz

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.

Diodes are also used as a radiation detector in radiotherapy: https://oncologymedicalphysics.com/diode-detectors/

Also the octaver…

https://www.geocities.ws/diygescorp/diodeoctaveup.gif

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.

And particle accelerators ! They mostly detect gamma radiation, and they are used in conjunction with other detectors (ram chips, mosfets)

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.

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 :)

With some capacitors you can build a voltage multiplicator

https://en.wikipedia.org/wiki/Voltage_multiplier

I went up 4:30 am today for a flight to Gothenburg, pretty tired and slow... and you and me both.

Stereo decoder. You feed L+R and L-R to the corners of Full Bridge Rectifier and out comes Left and Right.

I heard his voice while reading this.

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.

They certainly do… I’ve few in my Eurorack synth

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.

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.

You can also use a bunch in series as a cheap voltage dropper (eg to make a PC fan run slower/quieter).

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?

> 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.

> 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.

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.

This article reads like study notes for the Canadian Advanced ham license exam. It's a great crash course on diodes.

> 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..."

> 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.

I misread the title at first and forwarded this to my wife.