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Uses of the P-N Junction Diode

A junction diode is an electronic component that limits current flow to one direction. It consists of two joined slivers of silicon, one treated to prefer positive charges and the other to prefer negative charges, so electronics designers call it a P-N junction diode. Because its action is simple and basic, it makes many fundamentally useful electronic circuits possible.

Rectifier
- Electronic circuits run on direct current (DC), not the alternating current (AC) available from your household electrical outlets. Batteries produce DC, but they have limited lifetime and power capacity. Most electronic devices rely on a device called a rectifier that converts AC to DC. A rectifier arranges one or more P-N junction diodes so they pass AC current when it flows one way but block it in the opposite direction. The result is a one-way current with a 60 hertz ripple. Subsequent filtering and regulation circuits remove most of the ripple, leaving a steady DC voltage well-suited for powering the most sensitive electronic devices.
Radio Detector
- AM radio uses a scheme called amplitude modulation to broadcast sound over high-frequency radio waves. The frequency of the radio signal, called the carrier, is hundreds of times greater than the sound frequency, called the modulator. To retrieve the sound from the broadcast signal, the radio has a diode-based detector circuit. It blocks the carrier signal and filters the high frequencies out, leaving only the audible sounds of speech and music.
Electronic Switch
- A solar panel can charge a battery, but when the sun goes down, the panel stops producing electricity and becomes a load on the battery, draining it. A diode placed in the circuit turns on when current flows from the solar panel to the battery and turns off when the battery's current tries to flow back through the panel. This electronic switching action preserves the battery's charge.
Voltage Multiplier
- A pair of P-N junction diodes, properly connected, doubles the peak-to-peak voltage of an incoming alternating current and converts it to DC. For example, an AC signal with a peak-to-peak voltage of 10 volts becomes a 20-volt DC signal. An arrangement of three diodes triples the voltage. A circuit called the Cockroft-Walton voltage multiplier increases voltage in stages: the more stages, the more voltage it produces. A well-designed Cockcroft-Walton multiplier can generate hundreds of thousands of volts.

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