Diodes – Rectifier – LEDs – Zener

Diodes easily conduct current in one direction (forward biased) but not the other (reverse biased). The exception being zener (sometimes called avalanche) diodes, which still passes current while forward biased, but can also safely pass some current while reverse biased, once their zener voltage is exceeded.

  • Rectifier
  • LEDs
  • Zener
  • Schottky

Rectifier

Rectifier diodes are made especially to rectify (only allow current in one direction). They still have limitations though of course. They usually still block about 0.7V while forward biased, and have a limit to how much voltage they can block while reverse biased. Make sure to check the datasheet for the part number you are using, to verify that it can block the voltage you will be using, and can handle the current you will demand of it.

LEDs

LED stands for Light Emitting Diode. LEDs are relatively poor diodes, but while forward biased, they produce light. They block more voltage while forward biased than other diodes, typically about 1.5V to 3.2V. LEDs should be limited to 20mA or less unless otherwise indicated.

Zener

Zener diodes are used while reverse biased. They block a voltage based on their rated zener voltage. They come in a wide range of values of zener voltages, much like resistors come in a wide range of resistances. When a higher voltage than the zener voltage is applied to the zener diode, it starts conducting current as needed to hold the voltage the same as the zener voltage at that node. It can be thought of as a voltage release valve.

Schottky

Schottky diodes are used just like rectifier diodes, but with the benefit of blocking less voltage while forward biased. Typically about 0.3V instead of approx. 0.7V. This results in less power loss, but schottky diodes don’t block reverse voltage quite as well as rectifiers.

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