Electronics notes/Diodes

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This is for beginners and very much by a beginner.

It's intended to get an intuitive overview for hobbyist needs. It may get you started, but to be able to do anything remotely clever, follow a proper course or read a good book.

Some basics and reference: Volts, amps, energy, power · Ground · batteries · resistors · changing voltage · transistors · fuses · diodes · varistors · capacitors · inductors · transformers · baluns · amplifier notes · frequency generation · skin effect

And some more applied stuff:

IO: Input and output pins · wired local IO · wired local-ish IO · ·  Various wireless · 802.11 (WiFi) · cell phone

Sensors: General sensor notes, voltage and current sensing · Knobs and dials · Pressure sensing · Temperature sensing · humidity sensing · Light sensing · Movement sensing · Capacitive sensing · Touch screen notes

Actuators: General actuator notes, circuit protection · Motors and servos · Solenoids

Some stuff I've messed with: Avrusb500v2 · GPS · Hilo GPRS · JY-MCU · DMX · Thermal printer ·

Noise stuff: Stray signals and noise · sound-related noise names · electronic non-coupled noise names · electronic coupled noise · ground loop · strategies to avoid coupled noise · Sampling, reproduction, and transmission distortions

Audio notes: See avnotes

Microcontroller and computer platforms Arduino and AVR notes · ESP series notes · STM32 series notes · · · ·

Less sorted: device voltage and impedance, audio and otherwise · electricity and humans · power supply considerations · Common terms, useful basics, soldering · PLL · pulse modulation · signal reflection · resource metering · SDR · Project boxes · Unsorted stuff

See also Category:Electronics.

Types and materials

Silicon diode

Common, cheap.

Forward voltage drop of about 0.7V.

Germanium diode

Forward voltage drop of about 0.3V.

Avalance breakdown (behaviour) / avalanche diode (type)

Avalance diodes usually refer to diodes that are made to imitate Zener-like behaviour, but which will work for higher voltages (100 ~ 300V) than Zeners can.

Avalance diodes may be found categorized as (or referred to) as Zener diodes.


Zener diode (type/behaviour)

A Zener diode acts like a normal diode in forward bias, and in reverse bias will conduct only if the voltage is over a known breakdown voltage - a behaviour known asthe Zener/avalance effect.

Most other diodes show a similar effect, but with different specs that are more finicky to use; Zeners in the other hand are designed to easily use this effect and to work within the reverse breakdown region.

Zeners are often used when this property is used as a feature rather than a problem. Useful for voltage clamping, as voltage references, simple (shunt) regulation (with low currents).


Schottky diode (type)


Forward voltage drop on the order of 0.15V - 0.45V(verify).


Bypass diode / (flyback) protection / catch / snubber / freewheeling / suppressor diode (application)

A bypass diode refers to a diode used to avoid problems that can stem from reverse biasing.

For example, in a series of solar cells, shading one cell among multiple leads to it to be (relatively) reverse biased, meaning it gets fed current from the others, which would heat it and may eventually damage it. A bypass diode in parallel makes the diode-solarcell pair safer as it lets the current-in-the-wrong-direction pass alongside the cell.

You may have preference for a fast-acting diode (e.g. Schottky) to minimize the time the reverse bias is applied.

Sometimes you may also care about low voltage drop (which can matter e.g. in battery applications). If reaction time is not so important (or low cost is considered more important), cheap general-purpose diodes such as the 1N400x series can be used.

A flyback/protection diode refers specifically to reverse biasing from inductive circuits, particularly electromagnetic components (coils on relays, solenoids, and motors) to kick noticable power into the circuit, which can cause reverse biasing and voltage spikes where they normally wouldn't be (and high enough to kill various components, including transistors).

A protection diode is placed in parallel with the inductive component, reverse biased to how you drive it (in the wrong directon in terms of the power supply); once the inductive element tries reverse bias the power, it conducts directly (shorts) to itself via the diode. For magnetic fields, this means that the collapse of the magnetic field is slowerd(verify). You are effectively making a sort of RC circuit, so less resistance makes for less of a spike, but more current on the diode. For general-purpose solutions it is safer to choose a larger diode than to add resistance, partly because you would need power resistors.

Protection diodes should

  • have a voltage rating of at least the voltage you are applying (about the same is usually good enough, a little more can't hurt)
  • and be able to take a decent load - may well be a few amps for a short while (depends a lot on the load)
  • be robust to reverse biasing (themselves)

If the load is bidirectoinal (e.g. bidirectional motor driver) then the flyback can happen in either direction, and you can't protect it in the way described above. For example, in the case of a H-bridge driver, you need four diodes for protection in both directions.


See also:

Clamp diode (application)

Voltage clamping diodes (application)


Rectifier bridge (simple design)



Photoresistors, a.k.a. Light Dependent Resistors (LDR), Cadmium Sulfide cells (CdS)