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A diode allows current to flow through it in one direction only. Two diodes are shown below that are commonly used in electronic projects. The diode on the top has the part number 1N4148 and the diode below it is a 1N4007.

Silicon diodes

Diode Schematic Symbol

The schematic symbol for a diode is shown below. Notice the similarity between the diode symbol and the LED symbol. The LED is a special type of diode.

LED schematic symbol

Diode Polarity

A diode has a cathode (-) and anode (+). In the schematic symbol, the tip of the triangle with the line on top of it is the cathode. The cathode is marked on the body of a diode by a band as shown below.

Diode polarity

Current can flow from the anode to the cathode only and never from the cathode to the anode – the diode is like a one way valve.