002: Diodes, especially LED-rectifier forward-reverse bias

Diodes are electric components that typically conduct current very easily in one direction (forward biased), while blocking lot of voltage, and thus current, in the other direction (reverse biased).

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Basic electronics circuit fragments and simple circuits 2 diagram covering rectifier zener and light emitting diodes LEDs by electronzap electronzapdotcom
Basic electronics circuit fragments and simple circuits 2 diagram covering rectifier zener and light emitting diodes LEDs by electronzap electronzapdotcom
  • Forward biased: Anode (+) while cathode (-)
  • Reverse biased: Cathode (+) while Anode (-)
  • Anode is the side without a strip for most dioded and has a longer lead for untrimmed indicator LEDs.
  • Cathode side has a band/stripe that is usually gray (for plastic) or black (for glass body) diodes. The LED cathode is a shorter lead if untrimmed, and possibly a flatten edge along the rim.
Rectifier diode and LED schematic symbols and common appearance with forward biased polarity diagram by electronzap electronzapdotcom
Rectifier diode and LED schematic symbols and common appearance with forward biased polarity diagram by electronzap electronzapdotcom

This kit has most of the diodes and transistors I use in my videos. As an Amazon Associate I earn from qualifying purchases so please use this link if you want to check it out!

Using a diode to pass current in one direction, while blocking in the other, is called “rectification”. Rectifier diodes are made to rectify circuits especially well as long as you stay within the limits of the particular rectifier. Use the part number to check the manufacturer’s datasheet for exact values.

LED (light emitting diodes) are made specifically to light up when current is passed through them while forward biased. They will block some voltage while reverse biased, but the voltage should still be kept low to prevent damage.

YouTube video covering this topic in much more detail

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Electronics course 2 rectifier diode and LED forward and reverse biased explained with multimeter

Some notes related to the video above.

  • Forward voltage – the small amount of voltage a diode still ends up blocking while forward biased (approx. 0.7V for the most common silicon diodes).
  • Breakdown voltage – How much voltage is expected to start forcing current while a particular diode is reverse biased, and likely destroying it. Some diodes (zener) however, are made to conduct some current safely while reverse biased.
  • 1N4001 rectifier diodes are commonly included with electronics kits. Being silicon based, they have a forward voltage about 0.7V. And then while reverse biased should block up to about 50V. Maximum current of 1A while forward biased. As always, check component datasheets to verify that specifications given are accurate.
  • Indicator LEDs are usually rated for 20mA current while forward biased. Red LEDs have a forward voltage of about 2V while green LEDs have about a 3V forward voltage.
  • The power supply voltage is split up among series components.
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