The diode, explained simply
A diode lets current flow in one direction only. Learn its forward voltage, how to spot anode and cathode, and its uses: protection, rectification, LEDs, Zener.
How does it work?
A junction of two semiconductors (P and N). Forward-biased (anode to cathode), it conducts once the voltage exceeds its threshold: about 0.7 V for silicon, 0.3 V for a Schottky. Reverse-biased, it blocks.
Finding the polarity
The band (grey or white stripe) on the body marks the cathode. On the symbol, the bar is the cathode. On an LED, the longer leg is the anode (+).
Diode families
Rectifier (1N4007, 1 A); fast signal (1N4148); Schottky (1N5819, low drop); Zener (regulates a voltage, e.g. 5.1 V); LED (emits light, 2–3 V drop).
What is it used for?
Protecting against reversed batteries, rectifying AC (bridge rectifier), absorbing motor or relay spikes, clamping a voltage with a Zener.
Flip an LED in the simulator and see why it stays off.
Try it freeFAQ
How do I test a diode with a multimeter?
Diode mode: about 0.5–0.7 V forward, "OL" in reverse. Two low readings: shorted diode; two "OL": open diode.
Is an LED a diode?
Yes, a light-emitting diode. It needs a series resistor to limit its current.