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Diodes

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Diode Properties

Diodes allow current to flow in only one direction.
Forward biased silicon diodes have 0.7 Volts (700mV) across them.
Diodes protect circuits from incorrect polarity power connection.
Electrons flow against the direction of the arrow.
Diodes convert A.C. into D.C. by blocking one direction of current flow.
Diodes protect semiconductors from damage caused by high back-emf voltages by allowing the inductor current to die away gradually.
Zener diodes provide an accurate reference voltage.
Light emitting diodes emit light. D'Oh!
LASER diodes emit coherent monochromatic light.
Photo-diodes are used as light sensors.
PIN diodes are used as really sensitive and high speed light sensors.
Lit LEDs have approximately 2 Volts across them.
Diodes demodulate Amplitude Modulated radio signals.

Diode Symbols

Diode Symbols.gif

Diode Types

Various Diodes

Rectifier (1 Amp)
Rectifier (5 Amp)
Rectifier (Bridge)
Rectifier (Bridge - another one)
Zener Diode (The small one)

Diode Ratings

Diodes have a ...

forward voltage drop of about 0.7 volts (typical silicon diodes)
maximum safe continuous forward current.
maximum safe peak forward current - important for switch-on current surges.
maximum safe reverse breakdown Voltage.
maximum safe heat dissipation.

Normal diodes are destroyed if they break down.
Zener diodes are reverse biased and are designed to operate in their breakdown region without damage.
In high frequency circuits, the diode's capacitance might become important or useful.

Diode Characteristics

The graph below shows the current/voltage characteristics of a typical silicon diode. The reverse leakage current has been exaggerated to make it show on the graph. The forward voltage is about 0.7 volts. The reverse breakdown voltage varies between different diode types. The range of breakdown values goes from a few Volts to over 1000 Volts.