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.
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!
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.
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.
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.
Audio transformers are available both on Aliexpress and Ebay, although I would probably trust more a Triad TY-250P which is about €5 each at Mouser.
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.)
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.
https://opg.optica.org/optcon/fulltext.cfm?uri=optcon-1-7-15...
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.
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.
https://www.cedarlakeinstruments.com/archives/841
https://www.monolithicpower.com/en/learning/mpscholar/analog...
A combination of "what's the simplest thing that could possibly work?" and "well they didn't say you couldn't..."
What kind of 33609 clone do you have?
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)
I’ve heard good things about “Practical Electronics for Inventors” but haven’t gone through it myself.
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.
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).
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?
> 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 50°C 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 150°C. Minus 25°C ambient leaves us 125°C. Divided by 50°C/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.
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.
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.
How completely unintuitive.
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.
> 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.
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.
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.
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.
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.
Maybe we're saying the same thing in different ways.
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.
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.
AJH Synth Sonic V Diode Ladder Filter. (IMHO AJH make the best eurorack filters out there..)
Any good suggestions on resources talking about building complex digital logic out of something more suitable?
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.
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...
I'm not called the LED Punisher without reason!
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.
